Physical Geography
Physical Geography
Similar topic to my ecology topic from a few years ago. Really struggling for motivation. Hoping this helps. Will hopefully go through all my 26 lectures today and tomorrow, and maybe even time for some tests. Feel free to correct errors or ask any related questions at all. I think I'll create topics for each of my subjects, since this does give me some extra motivation to study.
Geomorphology Lecture 1;
Introduction and energy.
Geomorphology is the study of changing landscapes and the causes of landscapes looking the way that they do, including topography and relief.
Key Landform determinates.
Materials - the material and the structure of the material have significant impacts on geomorphology. So there can be direct impacts, for example in the erosion of limestone due to water, or their can be impacts due to differences between materials - such as one material eroding faster than another, causing a gully and meaning that water only flows through the softer material, eroding it further. Structure can result in earthquakes as well.
Processes. There are two types of processes - endogenetic, and exogenetic. Endogenetic are processes from within the Earth such as volcanoes and earthquakes. Exogenetic are things that start outside of Earth, especially atmospheric things - rain, wind etc. Australia is very old and has no recent mountain building, but the Northern Hemisphere is much younger and landforms have evolved more recently. Processes can continue to have a significant influence on the landscape long after the actual process has stopped. For example you can still see the evidence from glaciations in Tasmania that occurred over 10,000 years ago.
Time. Over time different processes act on the same piece of land. What we see now is the result of those different processes overlaid on top of each other.
Energy
Is usually diffused over long periods of time. There are a number of sources; Earth's internal heat, which drives plate tectonics, earthquakes, etc. Gravity and inertial forces. Gravity obviously results in things falling down. Inertial forces such as the Coriolis effect. Gravity can be extraterrestrial as well, such as with the tides. Solar energy. Represents 99.8% of all energy in the geomorphic systems. Due to angle etc. causes energy gradients that drive climate systems and hydrological cycle (water cycle), which is particularly important for geomorphology. Energy gradients can be latitudinal - ie. places closer to poles get less energy. Altitudinal - higher up you go there is less heat. Seasonal - due to change in Earth's axis meaning you get less energy from sun. Land/sea contrasts - land is typically warmer, radiates more sunlight etc. continental vs maritime etc. Hydrological cycle can transfer energy through the system. Sunlight shines on ocean causing evaporation, then rainfall and erosion - electromagnetic radiation transferred in to heat energy, then kinetic, then potential (as well as heat changes), then kinetic again, causing erosion.
Climate changes when energy is not balanced.
Thresholds
Processes can continue slowly until they reach a "tipping" point where change can be massive. Therefore you can't extrapolate from a point and predict the future very easily. eg. plates are moving at 2 inches a year, therefore in 100 years they will have moved 200 inches - movement could be much greater if a threshold is reached. Impacts can be very rapid and massive; high impact and low frequency. Thresholds can be intrinsic or extrinsic. Intrinsic thresholds occur due to internal impacts within the system. eg. a surging glacier due to increase in meltwater acting as a lubricant for the glacier. Extrinsic thresholds occur due to events outside of the system. eg. Cutting down the trees on a slope, followed by heavy rain can cause a landslide if threshold is reached.
Landforms are conditioned by "universal" laws and by also by the local circumstances that condition the pathway along which the landform evolves.
Introduction and energy.
Geomorphology is the study of changing landscapes and the causes of landscapes looking the way that they do, including topography and relief.
Key Landform determinates.
Materials - the material and the structure of the material have significant impacts on geomorphology. So there can be direct impacts, for example in the erosion of limestone due to water, or their can be impacts due to differences between materials - such as one material eroding faster than another, causing a gully and meaning that water only flows through the softer material, eroding it further. Structure can result in earthquakes as well.
Processes. There are two types of processes - endogenetic, and exogenetic. Endogenetic are processes from within the Earth such as volcanoes and earthquakes. Exogenetic are things that start outside of Earth, especially atmospheric things - rain, wind etc. Australia is very old and has no recent mountain building, but the Northern Hemisphere is much younger and landforms have evolved more recently. Processes can continue to have a significant influence on the landscape long after the actual process has stopped. For example you can still see the evidence from glaciations in Tasmania that occurred over 10,000 years ago.
Time. Over time different processes act on the same piece of land. What we see now is the result of those different processes overlaid on top of each other.
Energy
Is usually diffused over long periods of time. There are a number of sources; Earth's internal heat, which drives plate tectonics, earthquakes, etc. Gravity and inertial forces. Gravity obviously results in things falling down. Inertial forces such as the Coriolis effect. Gravity can be extraterrestrial as well, such as with the tides. Solar energy. Represents 99.8% of all energy in the geomorphic systems. Due to angle etc. causes energy gradients that drive climate systems and hydrological cycle (water cycle), which is particularly important for geomorphology. Energy gradients can be latitudinal - ie. places closer to poles get less energy. Altitudinal - higher up you go there is less heat. Seasonal - due to change in Earth's axis meaning you get less energy from sun. Land/sea contrasts - land is typically warmer, radiates more sunlight etc. continental vs maritime etc. Hydrological cycle can transfer energy through the system. Sunlight shines on ocean causing evaporation, then rainfall and erosion - electromagnetic radiation transferred in to heat energy, then kinetic, then potential (as well as heat changes), then kinetic again, causing erosion.
Climate changes when energy is not balanced.
Thresholds
Processes can continue slowly until they reach a "tipping" point where change can be massive. Therefore you can't extrapolate from a point and predict the future very easily. eg. plates are moving at 2 inches a year, therefore in 100 years they will have moved 200 inches - movement could be much greater if a threshold is reached. Impacts can be very rapid and massive; high impact and low frequency. Thresholds can be intrinsic or extrinsic. Intrinsic thresholds occur due to internal impacts within the system. eg. a surging glacier due to increase in meltwater acting as a lubricant for the glacier. Extrinsic thresholds occur due to events outside of the system. eg. Cutting down the trees on a slope, followed by heavy rain can cause a landslide if threshold is reached.
Landforms are conditioned by "universal" laws and by also by the local circumstances that condition the pathway along which the landform evolves.
Geomorphology lecture 2
Late Cainozoic
Climate change; Climate change is the variance of annual average conditions over time. Changing weather and changing seasons (eg. summer to autumn) are not climate change. Climate change can be natural or anthropogenic. The late cainozoic period is dominated by climate change - especially a number of glacial climate periods (ice ages). Evidence in glacial systems, sea levels, vegetation (pollen records etc.), deserts, lakes, lake levels, rivers, animal extinctions etc.
In Australia there were only natural changes until 50 kya (1000 years ago), after that many changes are caused by humans.
Ice ages are caused by a series of cycles - Orbit of Earth around Sun variation - cycle lasts about 100ky. Wobble of axis - Earth's axis changes tilt making seasons more or less pronounced - There are two different cycles, one is 26ky and the other is 40ky. Ice ages typically occur when the cycles align in a cold spots together (more pronounced seasons is cold spot because of the latent heat qualities of water - ie. colder winters mean more ice, and energy is absorbed in melting that ice instead of warming temps - ice forms due to a lack of energy, so doesn't require energy to freeze - so more ice means less heat energy in the system, even though the total annual energy may be the same).
Glacial climate periods are times when the temperatures are really cool, it doesn't matter if there are actual glaciers or not (although that's how they were initially defined - but it's a global thing, and glaciers are the consequence of moisture in the air, and that doesn't occur everywhere).
A "glaciation" is when glaciers are expanding - this is local and based around an actual glacier expanding, not necessarily temperature related (because it depends on moisture).
Cenozoic is Tertiary, Quaternary and periods - last 65 million years. Quaternary is the last 1.8 million, broken up into the Pleistocene and holocene. Holocene is last 10,000 years although we may have entered a new epoch - anthropocene.
There have been 18 major glacial/interglacial cycles in the late tertiary.
In Tasmania the earliest known glaciation was 30 mya but the main glaciations were in the late pliocene. The last glacial period was from 20,000 years ago to 10,000 years ago, but the last glacier finished about 15 kya. Due to the difficulty in dating glaciers in Tasmania, they are named after where they occurred rather than given a universal time. The holocene is the epoch representing the last interglacial that we're still in. In the late cenozoic glacial periods have been the norm and interglacials have been the exception.
In cold periods geomorphology impacts are different. For example there is less vegetation which makes slopes less stable.
Periglacial conditions.
These were initially observed around glaciers but occur anywhere where the temperature regularly drops below 0 degrees. These are just cold climate conditions - the "glacial" part of their name is just a relic of their etymology. These are things like frost shattering where water goes into the cracks in rocks and then freezes, expanding and breaking the rocks. Periglacial include permafrost and seasonally cold places. Periglacial conditions are biggest when the temperature crosses 0 degrees most frequently, ie. when water freezes each night.
Salt crystals can have the same effect as ice crystals.
Soilfluction - loose soil gets wet and then freezes and particles get pushed apart. Causing soil flow and debris flow, especially when ice melts. Can occur on flat surfaces, but usually 5 to 30 degrees. Boulder slopes in Tasmania are caused by this process - soil was eroded from around them due to soilfluction. Fluvial systems carry fine sediment in interglacial periods but in glacial periods they carry much larger sediment - especially glaciers.
Evidence;
Temperature records are only 100 years old or so, so various proxies are needed. These have different resolutions and time frames so they overlap and can create continuous records. Oxygen isotopes is a good one. Oxygen comes in two main isotopes O16 and O18 - much more O16 than O18. Foraminiferal (deep see protists with shells, can be planktonic) take up oxygen in their shells. When it's colder they take in more O18. When they die their shells sink to the bottom of the ocean and form layers. The ratio of O18 to O16 can therefore be used to gauge the temperature. This record is very good because it's basically continuous and is found across the globe.
Land records are less accurate. One method is pollen records. Pollen is only preserved when it falls in wet conditions such as lakes and wetlands. The sediment cores give an impression of the local vegetation. Especially with more recent pollen where the same species or similar species are present we can guess the climate based on what was growing.
Radiometric dating is a more accurate dating system. There are a number of methods, such as carbon dating and uranium dating. Radiocarbon dating works because when rocks form they contain radioactive elements that then decay. The ratio of the radioactive elements to their products tells you how long they've been decaying for and thus the age.
You can also do rind dating. When a rock is broken and exposed to the air the outside starts to be weathered. By cutting into the rind and seeing how thick it is etc.
Late Cainozoic
Climate change; Climate change is the variance of annual average conditions over time. Changing weather and changing seasons (eg. summer to autumn) are not climate change. Climate change can be natural or anthropogenic. The late cainozoic period is dominated by climate change - especially a number of glacial climate periods (ice ages). Evidence in glacial systems, sea levels, vegetation (pollen records etc.), deserts, lakes, lake levels, rivers, animal extinctions etc.
In Australia there were only natural changes until 50 kya (1000 years ago), after that many changes are caused by humans.
Ice ages are caused by a series of cycles - Orbit of Earth around Sun variation - cycle lasts about 100ky. Wobble of axis - Earth's axis changes tilt making seasons more or less pronounced - There are two different cycles, one is 26ky and the other is 40ky. Ice ages typically occur when the cycles align in a cold spots together (more pronounced seasons is cold spot because of the latent heat qualities of water - ie. colder winters mean more ice, and energy is absorbed in melting that ice instead of warming temps - ice forms due to a lack of energy, so doesn't require energy to freeze - so more ice means less heat energy in the system, even though the total annual energy may be the same).
Glacial climate periods are times when the temperatures are really cool, it doesn't matter if there are actual glaciers or not (although that's how they were initially defined - but it's a global thing, and glaciers are the consequence of moisture in the air, and that doesn't occur everywhere).
A "glaciation" is when glaciers are expanding - this is local and based around an actual glacier expanding, not necessarily temperature related (because it depends on moisture).
Cenozoic is Tertiary, Quaternary and periods - last 65 million years. Quaternary is the last 1.8 million, broken up into the Pleistocene and holocene. Holocene is last 10,000 years although we may have entered a new epoch - anthropocene.
There have been 18 major glacial/interglacial cycles in the late tertiary.
In Tasmania the earliest known glaciation was 30 mya but the main glaciations were in the late pliocene. The last glacial period was from 20,000 years ago to 10,000 years ago, but the last glacier finished about 15 kya. Due to the difficulty in dating glaciers in Tasmania, they are named after where they occurred rather than given a universal time. The holocene is the epoch representing the last interglacial that we're still in. In the late cenozoic glacial periods have been the norm and interglacials have been the exception.
In cold periods geomorphology impacts are different. For example there is less vegetation which makes slopes less stable.
Periglacial conditions.
These were initially observed around glaciers but occur anywhere where the temperature regularly drops below 0 degrees. These are just cold climate conditions - the "glacial" part of their name is just a relic of their etymology. These are things like frost shattering where water goes into the cracks in rocks and then freezes, expanding and breaking the rocks. Periglacial include permafrost and seasonally cold places. Periglacial conditions are biggest when the temperature crosses 0 degrees most frequently, ie. when water freezes each night.
Salt crystals can have the same effect as ice crystals.
Soilfluction - loose soil gets wet and then freezes and particles get pushed apart. Causing soil flow and debris flow, especially when ice melts. Can occur on flat surfaces, but usually 5 to 30 degrees. Boulder slopes in Tasmania are caused by this process - soil was eroded from around them due to soilfluction. Fluvial systems carry fine sediment in interglacial periods but in glacial periods they carry much larger sediment - especially glaciers.
Evidence;
Temperature records are only 100 years old or so, so various proxies are needed. These have different resolutions and time frames so they overlap and can create continuous records. Oxygen isotopes is a good one. Oxygen comes in two main isotopes O16 and O18 - much more O16 than O18. Foraminiferal (deep see protists with shells, can be planktonic) take up oxygen in their shells. When it's colder they take in more O18. When they die their shells sink to the bottom of the ocean and form layers. The ratio of O18 to O16 can therefore be used to gauge the temperature. This record is very good because it's basically continuous and is found across the globe.
Land records are less accurate. One method is pollen records. Pollen is only preserved when it falls in wet conditions such as lakes and wetlands. The sediment cores give an impression of the local vegetation. Especially with more recent pollen where the same species or similar species are present we can guess the climate based on what was growing.
Radiometric dating is a more accurate dating system. There are a number of methods, such as carbon dating and uranium dating. Radiocarbon dating works because when rocks form they contain radioactive elements that then decay. The ratio of the radioactive elements to their products tells you how long they've been decaying for and thus the age.
You can also do rind dating. When a rock is broken and exposed to the air the outside starts to be weathered. By cutting into the rind and seeing how thick it is etc.
Lecture 3
Glaciers and deserts
Glaciers and deserts have a lot of similarities despite seeming completely different. Also in the pleistocene (2.6mya to 10 kya - 10kya=start of human agriculture. I presume that the human tag is added because the head of this unit is an ant expert, and they also farm things. Unrelated but amusing). In times of low temperatures moisture is typically blown across the land, and rains when it reaches saturation point (not sure if that's the right term), especially mountains, creating glaciers in the mountains and then a rain shadow next to the mountains that become a desert. Hence often glaciers were next to deserts.
Glaciers;
Glaciers can be divided into two types based on their morphology (form and structure). Unconstrained and constrained. Unconstrained are glaciers such as ice caps - see the Arctic, Antarctic, Greenland etc. Constrained are the glaciers we think of when we talk about glaciers. ie. rivers of ice. Ice shelves are unconstrained glaciers that are floating.
Due to gravity, structure etc. When ice is in a pile forces act to flatten it out. In an unconstrained environment this leads to it filling out and covering continent, pushing icebergs off etc. In a constrained environment this leads to it flowing, usually downhill.
Constrained glaciers can be valley glaciers - ie. flowing like a river and carving or in a valley. Cirque glaciers - accumulation of ice on the leeward side of the slope (forming circle shape etc.), and niche glaciers, which are just tiny cirque glaciers.
Glaciers can also be classified as "cold" or "warm." A cold glacier is frozen to the ground below it and can't move. A warm glacier has meltwater under it, and so can move. Obviously there is a range between.
Glaciers are usually formed by snow that gets packed in tight, melts due to pressure and reforms as ice. They can only occur in places where water remains frozen all year round.
There are two parts to glaciers - the zone of accumulation where the snow is falling and there is more ice forming than going. Zone of ablation where there is more ice melting than accumulating - ie. the end. In the middle of these is the "equilibrium line" where the amount of ice arriving and leaving is the same. At this point the glacier is typically at its thickest and moving the fastest. Usually this line doesn't change with seasons and it leaves particular geological evidence - ie. change in slope of erosion.
Influences of flow.
Climate. At times when it is warmer there is also more precipitation so more ice (obviously still needs to be below 0 C). Slope - obviously steeper slope means more flow. Glaciers sometimes do flow uphill for short periods if there is a lot of pressure behind them - eg. after coming down a steep slope.
Flow mechanisms.
Glaciers flow in two ways; intragranular slip and intergranular slip. Intragranular slip is when the ice fractures and moves against itself. This is especially important for cold glaciers as it's the only way they can move. Intergranular is basal movement, slipping over the bed due to meltwater. This can occur due to temperatures or pressure - lots of ice build up means there is enough pressure to melt ice at the base of the glacier.
Regelation often occurs - this is where there is a bump in the bed. Ice pushes hard against it, creating high pressure, meltwater and movement etc. However on the opposite side there is no pressure so the water freezes again, but can flow deeply into cracks etc. before freezing. As the glacier moves the ice in the cracks gets pulled away, enhancing erosion.
Meltwater
Glaciofluvial systems - meltwater in the glacier. Can be supraglacial - on top, englacial - in the glacier, subglacial - on the bottom, marginal - on the sides, submarginal - underneath the edge (but on the edge) and proglacial - at the end of the glacier.
Glaciocustrine systems - ie. meltwater after the glacier has finished.
The speed of the glacier relates to the amount of work that it does. The faster the more work. Thickness and energy due to slope gradient also factors, as is the resistance of the substrate. More work=more erosion.
Erosion can smooth down surfaces, often with regulation on the other side - ie. smooth on the first side and rough on the leeward side. Often also creates groves.
Form structures such as arettes - ridge between two cirques. Horns - point between multiple cirques.
Glaciers can't turn much so they often bulldoze straight through rather than following topography. This can cause fjords to form at bends in glaciers where they are forced to turn - massive pressure so very deep erosion. Hanging valleys are when a small glacier meets a large glacier when melted leaves a small valley meeting a big valley.
Erosion occurs on the bed and sides of the glacier. The "snout" also pushes material in front of it. Material often also falls from the sides of the valley the glacier has formed on to the top of the glacier. The erosion by the glacier can weaken the sides of the valley and cause this to happen.
Till is sediments that are deposited directly by the glacier. Drift is sediments deposited by the glacier and by meltwater.
Ablation till is till frozen in the glacier but then surface melts, releasing it, but still on ice - can flow away with the water. Melt out till is when the glacier melts completely - the debris left behind. Lodgement/basal till is debris compacted into the ground by the glacier, due to the force, this is very hard.
Glacier boulders - rocks carried away from their origin by the glacier - can be "erratics" if does not belong in new area geologically.
Moraines are deposits of till. Can be lateral, medial, end or terminal. Terminal is furtherest down end moraine.
Ice sheets can also change landforms. Drumlins are ice sheet depositional features. Eskers are melt water deposition inside of caves inside the ice sheet. Kettle holes - kettle holes are formed when blocks of ice are left isolated as the glacier retreats. Sediment is deposited all around them and when the block melts it leaves a hole in the sediment. Walden Pond is an example of a kettle hole.
Deserts
Defined by lack of rain - not temperature. Lots of erosion and loose sediments. Because of this, when it does rain the rain causes very large amounts of erosion, many fluvial land forms. Wind is also a big factor causing a lot of erosion. Wind erosion often blows away all the smallest particles only leaving the bigger particles. This is called deflation. The big particles can create protect the small particles from the wind, so you can have a section of big particles followed by a section of small, etc.
Loess is the finest material, and is easily moved by wind. Can be important nutrient etc. - ie. Sahara loess helps fertilize Amazon basin.
Deposition forms dunes. Can be sedentary, mobile or migratory.
Many forms of dunes.
Star dunes - star shaped, caused by winds blowing in different directions
Longitudinal or Linear dunes - long parallel ridges. Especially found in trade wind deserts. Caused by shifting seasonal winds - blowing in one direction then changing to blow in a slightly different direction. Transverse Dunes - sloped up and then sharp dip - slopes up on windward side and sharp dip on slipface.
Barchan dunes - horn shaped with horns pointing with wind. Also gentle slope on wind side and deeper slope on wind side. Migrate.
Glaciers and deserts
Glaciers and deserts have a lot of similarities despite seeming completely different. Also in the pleistocene (2.6mya to 10 kya - 10kya=start of human agriculture. I presume that the human tag is added because the head of this unit is an ant expert, and they also farm things. Unrelated but amusing). In times of low temperatures moisture is typically blown across the land, and rains when it reaches saturation point (not sure if that's the right term), especially mountains, creating glaciers in the mountains and then a rain shadow next to the mountains that become a desert. Hence often glaciers were next to deserts.
Glaciers;
Glaciers can be divided into two types based on their morphology (form and structure). Unconstrained and constrained. Unconstrained are glaciers such as ice caps - see the Arctic, Antarctic, Greenland etc. Constrained are the glaciers we think of when we talk about glaciers. ie. rivers of ice. Ice shelves are unconstrained glaciers that are floating.
Due to gravity, structure etc. When ice is in a pile forces act to flatten it out. In an unconstrained environment this leads to it filling out and covering continent, pushing icebergs off etc. In a constrained environment this leads to it flowing, usually downhill.
Constrained glaciers can be valley glaciers - ie. flowing like a river and carving or in a valley. Cirque glaciers - accumulation of ice on the leeward side of the slope (forming circle shape etc.), and niche glaciers, which are just tiny cirque glaciers.
Glaciers can also be classified as "cold" or "warm." A cold glacier is frozen to the ground below it and can't move. A warm glacier has meltwater under it, and so can move. Obviously there is a range between.
Glaciers are usually formed by snow that gets packed in tight, melts due to pressure and reforms as ice. They can only occur in places where water remains frozen all year round.
There are two parts to glaciers - the zone of accumulation where the snow is falling and there is more ice forming than going. Zone of ablation where there is more ice melting than accumulating - ie. the end. In the middle of these is the "equilibrium line" where the amount of ice arriving and leaving is the same. At this point the glacier is typically at its thickest and moving the fastest. Usually this line doesn't change with seasons and it leaves particular geological evidence - ie. change in slope of erosion.
Influences of flow.
Climate. At times when it is warmer there is also more precipitation so more ice (obviously still needs to be below 0 C). Slope - obviously steeper slope means more flow. Glaciers sometimes do flow uphill for short periods if there is a lot of pressure behind them - eg. after coming down a steep slope.
Flow mechanisms.
Glaciers flow in two ways; intragranular slip and intergranular slip. Intragranular slip is when the ice fractures and moves against itself. This is especially important for cold glaciers as it's the only way they can move. Intergranular is basal movement, slipping over the bed due to meltwater. This can occur due to temperatures or pressure - lots of ice build up means there is enough pressure to melt ice at the base of the glacier.
Regelation often occurs - this is where there is a bump in the bed. Ice pushes hard against it, creating high pressure, meltwater and movement etc. However on the opposite side there is no pressure so the water freezes again, but can flow deeply into cracks etc. before freezing. As the glacier moves the ice in the cracks gets pulled away, enhancing erosion.
Meltwater
Glaciofluvial systems - meltwater in the glacier. Can be supraglacial - on top, englacial - in the glacier, subglacial - on the bottom, marginal - on the sides, submarginal - underneath the edge (but on the edge) and proglacial - at the end of the glacier.
Glaciocustrine systems - ie. meltwater after the glacier has finished.
The speed of the glacier relates to the amount of work that it does. The faster the more work. Thickness and energy due to slope gradient also factors, as is the resistance of the substrate. More work=more erosion.
Erosion can smooth down surfaces, often with regulation on the other side - ie. smooth on the first side and rough on the leeward side. Often also creates groves.
Form structures such as arettes - ridge between two cirques. Horns - point between multiple cirques.
Glaciers can't turn much so they often bulldoze straight through rather than following topography. This can cause fjords to form at bends in glaciers where they are forced to turn - massive pressure so very deep erosion. Hanging valleys are when a small glacier meets a large glacier when melted leaves a small valley meeting a big valley.
Erosion occurs on the bed and sides of the glacier. The "snout" also pushes material in front of it. Material often also falls from the sides of the valley the glacier has formed on to the top of the glacier. The erosion by the glacier can weaken the sides of the valley and cause this to happen.
Till is sediments that are deposited directly by the glacier. Drift is sediments deposited by the glacier and by meltwater.
Ablation till is till frozen in the glacier but then surface melts, releasing it, but still on ice - can flow away with the water. Melt out till is when the glacier melts completely - the debris left behind. Lodgement/basal till is debris compacted into the ground by the glacier, due to the force, this is very hard.
Glacier boulders - rocks carried away from their origin by the glacier - can be "erratics" if does not belong in new area geologically.
Moraines are deposits of till. Can be lateral, medial, end or terminal. Terminal is furtherest down end moraine.
Ice sheets can also change landforms. Drumlins are ice sheet depositional features. Eskers are melt water deposition inside of caves inside the ice sheet. Kettle holes - kettle holes are formed when blocks of ice are left isolated as the glacier retreats. Sediment is deposited all around them and when the block melts it leaves a hole in the sediment. Walden Pond is an example of a kettle hole.
Deserts
Defined by lack of rain - not temperature. Lots of erosion and loose sediments. Because of this, when it does rain the rain causes very large amounts of erosion, many fluvial land forms. Wind is also a big factor causing a lot of erosion. Wind erosion often blows away all the smallest particles only leaving the bigger particles. This is called deflation. The big particles can create protect the small particles from the wind, so you can have a section of big particles followed by a section of small, etc.
Loess is the finest material, and is easily moved by wind. Can be important nutrient etc. - ie. Sahara loess helps fertilize Amazon basin.
Deposition forms dunes. Can be sedentary, mobile or migratory.
Many forms of dunes.
Star dunes - star shaped, caused by winds blowing in different directions
Longitudinal or Linear dunes - long parallel ridges. Especially found in trade wind deserts. Caused by shifting seasonal winds - blowing in one direction then changing to blow in a slightly different direction. Transverse Dunes - sloped up and then sharp dip - slopes up on windward side and sharp dip on slipface.
Barchan dunes - horn shaped with horns pointing with wind. Also gentle slope on wind side and deeper slope on wind side. Migrate.
Geomorphology Lecture 4
Geological structure
Very important for landscape evolution - provides the "skeleton" for the landscape. Different rock types have different erosion rates etc. Position and shape of rocks also important.
Global scale features;
Continental features - tectonics etc. Cratons (plates), subduction zones, linear mountain ranges.
Crustal spreading. Rift zones, transform faults, large strike/slip faults - earthquakes, volcanoes etc.
Ocean spreading. Oceanic ridges, trenches, abyssal floor. Volcanic arcs.
Resulting landform/landscape scale features
Flat and homogeneous strata. Cliff and bench topography, waterfalls etc. Erosion leaving behind hard surfaces.
Tilted stratas - ie. on an angle but still flat.
Folded strata - ie. curved due to pressure.
Faulted strata - ie. with fractures through it and slipping.
Igneous structures - usually very hard and don't erode. Often intrude in to strata which can then erode around them. When coming up through strata is called a dyke. When spreading out across strata is called a sill.
Most structural landforms occur where erosion is dominate - ie. exogenic forces are faster than endogenic forces.
Features can pre dispose area to particular drainage patterns.
Granite rocks tend to be round because they have square structure to begin with. This means that if erosion is occurring equally around the rock then on edges and corners it is happening from two/three directions so occurs faster, so edges and corners get rounded off. Continues until rock is round, at which point erosion becomes uniform. Batholiths are giant granite formations.
Waterfalls occur where hard rock meets softer rock. Soft rock eroded away leaving hard rock.
Cuestas are ridges of tilted rock beds.
Fault-line scarps are not the same as fault scarps. Fault-line scarps look the same but are caused by erosion of softer material against harder material, while fault scarps are actually caused by tectonic faults.
Many processes can have acted on a landscape over time. This can confound drainage - ie. the drainage pattern might be caused by processes that all evidence for has now disappeared.
Drainage types;
Dendritic - tree like. Very efficient.
Rectangular - due to faults - water flows along faults etc.
Trellis - parallel streams with smaller streams running in to them.
Radial - usually found around volcanoes. Can continue after volcano completely erodes away. - Water flowing out and in circular motions
Annular - like radial but with faulting as well, so more structured.
Consequent streams - follows original structural slopes.
Subsequent streams - follows the weaker beds due to erosion - ie. many valley streams.
Obsequent stream - cuts into the cuesta face
Antecedent/superimposed. Relic of previous geology. Started in a rock structure that is now completely eroded, but it eroded through first, and so has also eroded a path through the rock below, which has no immediate explanation for why it's there. Can cut across anticlines if its erosion is faster than the folding is occurring. Very old.
Geological structure
Very important for landscape evolution - provides the "skeleton" for the landscape. Different rock types have different erosion rates etc. Position and shape of rocks also important.
Global scale features;
Continental features - tectonics etc. Cratons (plates), subduction zones, linear mountain ranges.
Crustal spreading. Rift zones, transform faults, large strike/slip faults - earthquakes, volcanoes etc.
Ocean spreading. Oceanic ridges, trenches, abyssal floor. Volcanic arcs.
Resulting landform/landscape scale features
Flat and homogeneous strata. Cliff and bench topography, waterfalls etc. Erosion leaving behind hard surfaces.
Tilted stratas - ie. on an angle but still flat.
Folded strata - ie. curved due to pressure.
Faulted strata - ie. with fractures through it and slipping.
Igneous structures - usually very hard and don't erode. Often intrude in to strata which can then erode around them. When coming up through strata is called a dyke. When spreading out across strata is called a sill.
Most structural landforms occur where erosion is dominate - ie. exogenic forces are faster than endogenic forces.
Features can pre dispose area to particular drainage patterns.
Granite rocks tend to be round because they have square structure to begin with. This means that if erosion is occurring equally around the rock then on edges and corners it is happening from two/three directions so occurs faster, so edges and corners get rounded off. Continues until rock is round, at which point erosion becomes uniform. Batholiths are giant granite formations.
Waterfalls occur where hard rock meets softer rock. Soft rock eroded away leaving hard rock.
Cuestas are ridges of tilted rock beds.
Fault-line scarps are not the same as fault scarps. Fault-line scarps look the same but are caused by erosion of softer material against harder material, while fault scarps are actually caused by tectonic faults.
Many processes can have acted on a landscape over time. This can confound drainage - ie. the drainage pattern might be caused by processes that all evidence for has now disappeared.
Drainage types;
Dendritic - tree like. Very efficient.
Rectangular - due to faults - water flows along faults etc.
Trellis - parallel streams with smaller streams running in to them.
Radial - usually found around volcanoes. Can continue after volcano completely erodes away. - Water flowing out and in circular motions
Annular - like radial but with faulting as well, so more structured.
Consequent streams - follows original structural slopes.
Subsequent streams - follows the weaker beds due to erosion - ie. many valley streams.
Obsequent stream - cuts into the cuesta face
Antecedent/superimposed. Relic of previous geology. Started in a rock structure that is now completely eroded, but it eroded through first, and so has also eroded a path through the rock below, which has no immediate explanation for why it's there. Can cut across anticlines if its erosion is faster than the folding is occurring. Very old.
Geomorphology Lecture 5
Volcanoes!
Areas around volcanoes have very good soil - implications for ecology etc.
Two types of igneous land forms - intrusions and extrusions.
Intrusions are not volcanic - magma does not reach surface, but comes up some way through the lithosphere. Can be discordant and cut through bedrock - eg. dykes, or concordant and spread across it - eg. sills. Mt. Wellington is an example of a sill. A mass of of an igneous intrusion is called a pluton. These structures are usually harder than their surrounding sediments and are revealed due to erosion.
Extrusions. Extrusions are volcanoes, and are formed when lava reaches the surface. They generally occur near the boundaries between plates - near fractures and faults etc. They can be caused by spreading - seafloor and continental rifts, and collisions including subduction. There are also hot spot volcanoes.
Active volcanoes have human records of eruption - within historical time.
Dormant volcanoes are geologically young, but have never been recorded to erupt.
Extinct volcanoes are old and not going to erupt again.
Landforms and the type of eruption depend on the stickiness of the lava, which depends on the silica content (SiO2). Greater than 67% SiO2 is acidic and forms rhyolites. 53% to 67% is intermediate and forms andersites. Less than 53% is basic and forms basalts.
Basalt comes in two textures - pahoehoe, which is fluid and Aa, which is sticky.
Gasses, water, mud and fragments of rock are also ejected.
Ash - particles less than 2mm
Lapilli - particles 2-64mm
blocks - greater than 64mm - also can be "bombs"
Unsure why those numbers are the cut off points...
Greater the silica means the greater the viscosity (stickiness). More viscosity means more explosive the eruption. Temperature also a factor - hotter temperature means lava is more fluid, colder has more viscosity. Gas content also relates to viscosity - more gas is more explosive.
Felsic lavas are highly viscous - lots of gas, explosive. Produce small, steep sided volcanoes with "tuff" - compacted volcanic particles less than 4 mm big. Mafic or basaltic lavas are very fluid so produce very flat volcanoes that spread out over large distances. Intermediate lavas produce classic volcanic cones with layers of ash then lava then ash etc.
Effusive eruptions are fluid.
Explosive eruptions are sticky (how many times did he say this?). Typically occur from subducted material near plate collision zones.
Central volcanoes have one lava pipe.
Fissures have more than one fissure (not a pipe) - usually produce large basalt plateaus - effusive.
Types;
Hawaiian - fluid and basaltic.
Icelandic - from fissures, fluid.
Strombolian - regular explosions of mild to modest intensity
Vulcanian - more siliceous but less explosive than strombolian. "Cauliflower" ash clouds.
Plinian - Explosive gas and pyroclastics up to 60km high.
Pelean - Fiery clouds of gas, lava and pyroclastics. Rapid release of gases suspends solid particles - fluidisation.
Krakatoan - most explosive.
Solfataric stage - just sulphurous gas - late stage.
Volcanic landforms
Shield volcanoes - gentle slopes with fluid lava. Can be massive.
Cinder cone - very tight slopes, small, explosive etc.
Composite - classical shape such as mt. Fuji. Intermediate lava.
Caldera - large craters. Can be formed by giant explosions but usually formed by large extinct volcanoes collapsing.
Lava tubes - fluid lava - cools on top and solidifies but warm in middle so keeps flowing - top part insulates insides so don't solidify, lava runs out leaving hollow tube.
lava can fill a valley, disrupting drainage and causing twin streams on either side of the lava flow.
Tasmania has a long volcanic history - 600mya Mt Read volcanics - major ore bodies in Tasmania. Triassic - intermediate volcanic action on east coast. Jurrasic dolerite intrusions. Tertiary - over 120 volcanoes identified. Evidence to be found around Sandy Bay etc.
Volcanoes!
Areas around volcanoes have very good soil - implications for ecology etc.
Two types of igneous land forms - intrusions and extrusions.
Intrusions are not volcanic - magma does not reach surface, but comes up some way through the lithosphere. Can be discordant and cut through bedrock - eg. dykes, or concordant and spread across it - eg. sills. Mt. Wellington is an example of a sill. A mass of of an igneous intrusion is called a pluton. These structures are usually harder than their surrounding sediments and are revealed due to erosion.
Extrusions. Extrusions are volcanoes, and are formed when lava reaches the surface. They generally occur near the boundaries between plates - near fractures and faults etc. They can be caused by spreading - seafloor and continental rifts, and collisions including subduction. There are also hot spot volcanoes.
Active volcanoes have human records of eruption - within historical time.
Dormant volcanoes are geologically young, but have never been recorded to erupt.
Extinct volcanoes are old and not going to erupt again.
Landforms and the type of eruption depend on the stickiness of the lava, which depends on the silica content (SiO2). Greater than 67% SiO2 is acidic and forms rhyolites. 53% to 67% is intermediate and forms andersites. Less than 53% is basic and forms basalts.
Basalt comes in two textures - pahoehoe, which is fluid and Aa, which is sticky.
Gasses, water, mud and fragments of rock are also ejected.
Ash - particles less than 2mm
Lapilli - particles 2-64mm
blocks - greater than 64mm - also can be "bombs"
Unsure why those numbers are the cut off points...
Greater the silica means the greater the viscosity (stickiness). More viscosity means more explosive the eruption. Temperature also a factor - hotter temperature means lava is more fluid, colder has more viscosity. Gas content also relates to viscosity - more gas is more explosive.
Felsic lavas are highly viscous - lots of gas, explosive. Produce small, steep sided volcanoes with "tuff" - compacted volcanic particles less than 4 mm big. Mafic or basaltic lavas are very fluid so produce very flat volcanoes that spread out over large distances. Intermediate lavas produce classic volcanic cones with layers of ash then lava then ash etc.
Effusive eruptions are fluid.
Explosive eruptions are sticky (how many times did he say this?). Typically occur from subducted material near plate collision zones.
Central volcanoes have one lava pipe.
Fissures have more than one fissure (not a pipe) - usually produce large basalt plateaus - effusive.
Types;
Hawaiian - fluid and basaltic.
Icelandic - from fissures, fluid.
Strombolian - regular explosions of mild to modest intensity
Vulcanian - more siliceous but less explosive than strombolian. "Cauliflower" ash clouds.
Plinian - Explosive gas and pyroclastics up to 60km high.
Pelean - Fiery clouds of gas, lava and pyroclastics. Rapid release of gases suspends solid particles - fluidisation.
Krakatoan - most explosive.
Solfataric stage - just sulphurous gas - late stage.
Volcanic landforms
Shield volcanoes - gentle slopes with fluid lava. Can be massive.
Cinder cone - very tight slopes, small, explosive etc.
Composite - classical shape such as mt. Fuji. Intermediate lava.
Caldera - large craters. Can be formed by giant explosions but usually formed by large extinct volcanoes collapsing.
Lava tubes - fluid lava - cools on top and solidifies but warm in middle so keeps flowing - top part insulates insides so don't solidify, lava runs out leaving hollow tube.
lava can fill a valley, disrupting drainage and causing twin streams on either side of the lava flow.
Tasmania has a long volcanic history - 600mya Mt Read volcanics - major ore bodies in Tasmania. Triassic - intermediate volcanic action on east coast. Jurrasic dolerite intrusions. Tertiary - over 120 volcanoes identified. Evidence to be found around Sandy Bay etc.
Geomorphology Lecture 6
Hillslopes
Hydrological cycle very important. Driven by solar radiation.
Water erodes surface etc. Also helps with chemical weathering. Biggest role is in vegetation levels - more water means more vegetation means less erosion - competing impacts regarding erosion. Means that when slopes are cleared there can be massive erosion.
Angle of slope has impact - less slope means water stationary for longer, more likely to form pools and evaporate without moving - less erosion.
Soil forms very slowly - about 2mm in 10,000 years. This means that erosion, especially due to land clearing, is a big problem.
Trees and vegetation also use water, which can lower erosion rates as well.
Snow melts slowly and so the water flow from snow is less intense than the same amount of precipitation as rain. Water flow density is critical for amount of erosion. Snow can also protect the ground from weathering and erosion. Roads and sealed surfaces often mean that there is no water retention in that place, so higher density water in other areas and so greater erosion. Force of rain drop can also have an impact on erosion and vegetation can protect the soil from this.
Rainsplash - impact of raindrops
Sheetwash - soil washed off in overland flow
rilling - very small channels as water collects and is captured in overland flow - smalls temporary streams etc. creating small erosion
gullying - larger irregular channels
tunnelling - collapsed subsurface piping - see Guatamala city "sinkholes" - not sinkholes, which are karst formations, but piping features.
Aquifers - porous material with water flowing through it. Pores must be connected. Water is usually slow moving. Can form around fractures and fissures. Aquaclude - material that cannot hold water. Confined aquifers are surrounded by aquacludes and not open to surface - under pressure. Unfconfined are open to surface, even if there may not be enough water to actually reach surface.
Mass movement of material
Fall - usually rocks, falling off cliff etc. Give rise to talus - fan of scree or debris at the base of cliffs
Slide/slump - includes avalanches etc. Can be transitional - ie. sliding parallel to surface below, or rotational - concave - steep and curved at base.
Flow - like water, usually involving water - fine sediments that behave as if liquid. Debris, earth, mud flow etc.
Hillslopes
Hydrological cycle very important. Driven by solar radiation.
Water erodes surface etc. Also helps with chemical weathering. Biggest role is in vegetation levels - more water means more vegetation means less erosion - competing impacts regarding erosion. Means that when slopes are cleared there can be massive erosion.
Angle of slope has impact - less slope means water stationary for longer, more likely to form pools and evaporate without moving - less erosion.
Soil forms very slowly - about 2mm in 10,000 years. This means that erosion, especially due to land clearing, is a big problem.
Trees and vegetation also use water, which can lower erosion rates as well.
Snow melts slowly and so the water flow from snow is less intense than the same amount of precipitation as rain. Water flow density is critical for amount of erosion. Snow can also protect the ground from weathering and erosion. Roads and sealed surfaces often mean that there is no water retention in that place, so higher density water in other areas and so greater erosion. Force of rain drop can also have an impact on erosion and vegetation can protect the soil from this.
Rainsplash - impact of raindrops
Sheetwash - soil washed off in overland flow
rilling - very small channels as water collects and is captured in overland flow - smalls temporary streams etc. creating small erosion
gullying - larger irregular channels
tunnelling - collapsed subsurface piping - see Guatamala city "sinkholes" - not sinkholes, which are karst formations, but piping features.
Aquifers - porous material with water flowing through it. Pores must be connected. Water is usually slow moving. Can form around fractures and fissures. Aquaclude - material that cannot hold water. Confined aquifers are surrounded by aquacludes and not open to surface - under pressure. Unfconfined are open to surface, even if there may not be enough water to actually reach surface.
Mass movement of material
Fall - usually rocks, falling off cliff etc. Give rise to talus - fan of scree or debris at the base of cliffs
Slide/slump - includes avalanches etc. Can be transitional - ie. sliding parallel to surface below, or rotational - concave - steep and curved at base.
Flow - like water, usually involving water - fine sediments that behave as if liquid. Debris, earth, mud flow etc.
Geomorphology lecture 7
Rivers, streams and shorelines
Basic elements of fluvial systems are;
Catchment divides, watershed, headwaters - hillslopes collect water and direct it downwards. The areas where the water that falls in that area will drain to the same point.
First order streams, dendritic networks - networks of tributaries that flow in to a main river. Order is based on number of streams - original stream is first order, when it meets another is second order etc.
Floodplains - alluvial (sediment accumulation) areas, low gradient that take excess water etc.
Water in these systems can erode, transport and deposit sediment.
Delta - fan shaped alluvial deposit at mouth of river.
Channels - trough like form which contains river and is shaped by the force of the river running through it. Can be alluvial or bedrock. Alluvial typically carry less water and are shallow so high flow causes water to spill on to flood plain.
Water flow can be laminar - all going in the same direction, or turbulent. Turbulent flow consumes a lot of energy as the water mixes etc. Often caused by rocks etc. in river. Very little energy remains for work - ie. erosion, transport and deposition.
Entrainment - sand particles etc - rolling, traction, saltation and suspension.
Obviously smaller material is easiest to transport and heaviest material is deposited first.
Hjulstrom curve shows the relationship between speed of water movement and and size of sediment which can be moved.
Sediment can be dissolved or solid. Dissolved load accounts for up to 30% of load. Solid load is mainly small material in suspension - usually more than 80% of solid load is carried like this. Saltation is usually small particles, but can be gravel in fast flows. Rolling likewise, but can be up to boulder sizes in fast flows.
Discharge, amount of water moving past a particular point is uniform in a river. Therefore when water is moving very fast the stream is narrow and shallow. When water is moving much slower it is wide and deep.
At deltas the sediment can block the channel causing many distributries - can be dendritic just like at the first order streams.
Tides.
Caused by pull of sun and moon. Sun has 47% of the impact as the moon. When forces align = spring tide. When counteract = neap tide.
Swell waves are caused by wind blowing across the top of the water - shear stress etc. Caused by wind velocity, duration of wind in constant direction, length of water (fetch). As waves get close to shore the bottom part drags on the surface, slowing it down while the top moves quicker, causing shape and eventual collapse.
Tsunamis - caused by earthquakes, very long waves.
Wave erosion and transport is similar to rivers.
Hydraulic action - force of waves hitting shore etc.
Attrition - breaking down particles in to smaller bits.
Abrasion - erosion as bits of rock hit other bits of rock due to hydraulic action.
Erosion land forms.
Shore platforms (wave cut platform) - gentle rock slopes that extend from high tide to low tide points - remnant of headland erosion - above waterline eroded away, below waterline remains. Much more erosion at and above waterline than below it.
Sea caves - common product of wave erosion at base of cliffs
Sea stacks - caused by wave refraction around headlands - focusing waves on point just behind headland etc.
Depositional land forms
Beaches - sand is carried to shore and the wave has more energy coming in than leaving, so ends up depositing more material than leaving.
Bar - under wave break - point of loss of energy and hence deposition
Berm - Beach crest - usually at top of high tide. Higher crests represent top of storm surges.
Baymouth bar - bar going all the way across a bar. Note that it's depositional so formed after bay, not inside of bay eroded leaving this.
Tombolo - beach between headland and island - underwater in low tide etc.
Current coastal environments are all very new. Relic coastal environments can be found away from coast due to tectonics and changing sea levels but because they're areas of high erosion when next to sea, always changing.
With many fluvial systems big rare events can change landscape much more than smaller frequent events. Single big floods etc. can create the river systems etc.
Rivers, streams and shorelines
Basic elements of fluvial systems are;
Catchment divides, watershed, headwaters - hillslopes collect water and direct it downwards. The areas where the water that falls in that area will drain to the same point.
First order streams, dendritic networks - networks of tributaries that flow in to a main river. Order is based on number of streams - original stream is first order, when it meets another is second order etc.
Floodplains - alluvial (sediment accumulation) areas, low gradient that take excess water etc.
Water in these systems can erode, transport and deposit sediment.
Delta - fan shaped alluvial deposit at mouth of river.
Channels - trough like form which contains river and is shaped by the force of the river running through it. Can be alluvial or bedrock. Alluvial typically carry less water and are shallow so high flow causes water to spill on to flood plain.
Water flow can be laminar - all going in the same direction, or turbulent. Turbulent flow consumes a lot of energy as the water mixes etc. Often caused by rocks etc. in river. Very little energy remains for work - ie. erosion, transport and deposition.
Entrainment - sand particles etc - rolling, traction, saltation and suspension.
Obviously smaller material is easiest to transport and heaviest material is deposited first.
Hjulstrom curve shows the relationship between speed of water movement and and size of sediment which can be moved.
Sediment can be dissolved or solid. Dissolved load accounts for up to 30% of load. Solid load is mainly small material in suspension - usually more than 80% of solid load is carried like this. Saltation is usually small particles, but can be gravel in fast flows. Rolling likewise, but can be up to boulder sizes in fast flows.
Discharge, amount of water moving past a particular point is uniform in a river. Therefore when water is moving very fast the stream is narrow and shallow. When water is moving much slower it is wide and deep.
At deltas the sediment can block the channel causing many distributries - can be dendritic just like at the first order streams.
Tides.
Caused by pull of sun and moon. Sun has 47% of the impact as the moon. When forces align = spring tide. When counteract = neap tide.
Swell waves are caused by wind blowing across the top of the water - shear stress etc. Caused by wind velocity, duration of wind in constant direction, length of water (fetch). As waves get close to shore the bottom part drags on the surface, slowing it down while the top moves quicker, causing shape and eventual collapse.
Tsunamis - caused by earthquakes, very long waves.
Wave erosion and transport is similar to rivers.
Hydraulic action - force of waves hitting shore etc.
Attrition - breaking down particles in to smaller bits.
Abrasion - erosion as bits of rock hit other bits of rock due to hydraulic action.
Erosion land forms.
Shore platforms (wave cut platform) - gentle rock slopes that extend from high tide to low tide points - remnant of headland erosion - above waterline eroded away, below waterline remains. Much more erosion at and above waterline than below it.
Sea caves - common product of wave erosion at base of cliffs
Sea stacks - caused by wave refraction around headlands - focusing waves on point just behind headland etc.
Depositional land forms
Beaches - sand is carried to shore and the wave has more energy coming in than leaving, so ends up depositing more material than leaving.
Bar - under wave break - point of loss of energy and hence deposition
Berm - Beach crest - usually at top of high tide. Higher crests represent top of storm surges.
Baymouth bar - bar going all the way across a bar. Note that it's depositional so formed after bay, not inside of bay eroded leaving this.
Tombolo - beach between headland and island - underwater in low tide etc.
Current coastal environments are all very new. Relic coastal environments can be found away from coast due to tectonics and changing sea levels but because they're areas of high erosion when next to sea, always changing.
With many fluvial systems big rare events can change landscape much more than smaller frequent events. Single big floods etc. can create the river systems etc.
Geogmorphology Lecture 8
Biogeomorphology
The interaction between geomorphic processes and organisms. Can be in either direction - the impact that land forms have on life, and the impact that life has on landforms.
Tectonics and biogeography. Has continents split up, plants and animals became isolated and evolved, but their closest relatives are on the continents that they broke away from most recently. Pagnea life, Gondwana life etc. Drifting continents also changes climate etc. For example Australia was further south and then drifted in to the mid latitude high pressure zone which has low moisture, so more arid conditions - created change in plant species towards species that require less water etc.
Bioerosion - erosion caused by biota
Bioprotection - protection of erosion
Bioconstruction - physical structures created by biota - coral reefs etc.
Vegetation and rivers
Forests suck up water, lowering water table etc.
Vegetation on sides of banks can stabilise them and prevent erosion. Large woody debris can scour banks and cause erosion etc.
Debris dams slow river flow, change patterns and increase sediment deposition at the slow part (also less further down stream).
Soil
Biotic contributions important part of soil formation
Contribution of organic material influences ph and structure
Bioturbation by soil invertebrates tends to mix soil horizons (layers)
Birds also create significant bioturbation with burrows etc. Also contribute nutrients to soil through guano
Plants can accelerate soil leaching through opening up soil, but organic matter in soils can fix nutrients and prevent leaching as well.
Vegetation on slopes has big impacts on erosion - see hillsopes. Respiration also causes increases of carbonic acid in karst areas (such as limestone) that increases erosion.
Coast
Coral reefs grow in three stages - initial growth. Destruction of reef due to storm etc, coral rubble deposited. New coral grows on deposits.
Darwin published explanation of coral reef formation in 1842. Subsidence. Reef forms and as it sinks due to weight continues to grow up, keeping pace with its sink.
Intertidal marshes, mud flats, mangroves
fine sediments deposited, slat resistant vegetation causes break from waves - low energy. Benthic and planktonic organisms bind sediments together creating a reduction in turbidity. Disruption can cause massive erosion.
Biogeomorphology
The interaction between geomorphic processes and organisms. Can be in either direction - the impact that land forms have on life, and the impact that life has on landforms.
Tectonics and biogeography. Has continents split up, plants and animals became isolated and evolved, but their closest relatives are on the continents that they broke away from most recently. Pagnea life, Gondwana life etc. Drifting continents also changes climate etc. For example Australia was further south and then drifted in to the mid latitude high pressure zone which has low moisture, so more arid conditions - created change in plant species towards species that require less water etc.
Bioerosion - erosion caused by biota
Bioprotection - protection of erosion
Bioconstruction - physical structures created by biota - coral reefs etc.
Vegetation and rivers
Forests suck up water, lowering water table etc.
Vegetation on sides of banks can stabilise them and prevent erosion. Large woody debris can scour banks and cause erosion etc.
Debris dams slow river flow, change patterns and increase sediment deposition at the slow part (also less further down stream).
Soil
Biotic contributions important part of soil formation
Contribution of organic material influences ph and structure
Bioturbation by soil invertebrates tends to mix soil horizons (layers)
Birds also create significant bioturbation with burrows etc. Also contribute nutrients to soil through guano
Plants can accelerate soil leaching through opening up soil, but organic matter in soils can fix nutrients and prevent leaching as well.
Vegetation on slopes has big impacts on erosion - see hillsopes. Respiration also causes increases of carbonic acid in karst areas (such as limestone) that increases erosion.
Coast
Coral reefs grow in three stages - initial growth. Destruction of reef due to storm etc, coral rubble deposited. New coral grows on deposits.
Darwin published explanation of coral reef formation in 1842. Subsidence. Reef forms and as it sinks due to weight continues to grow up, keeping pace with its sink.
Intertidal marshes, mud flats, mangroves
fine sediments deposited, slat resistant vegetation causes break from waves - low energy. Benthic and planktonic organisms bind sediments together creating a reduction in turbidity. Disruption can cause massive erosion.
Climate Lecture 1
Weather is the state of the atmosphere at a given place and time. It provides raw observations and is associated with instantaneous measurements of conditions. It is described by climatologists.
Climate is the generalisation of weather data over long periods of time. In a typical weather environment you get average conditions plus variation. Climate tries to explain them. Climate is what you expect, weather is what you get.
Scale is very important for climate and weather. Macroscale, mesoscale and microscale. Looking at things from a global scale to a continent scale to a local scale.
Typically the macroscale is dominated by horizontal movement. The microscale is dominate by vertical movement and the mesoscale is a mix of both. Scale in time is also important - diurnal time (day night), ENSO, solar cycles etc. Some of these are regular and some are irregular.
Earth's climate system can be broken in to many parts - atmosphere, hydrosphere, biosphere, cryosphere (ice), and lithosphere. There are also many feedbacks
Some definitions;
Temperature ; rate at which molecules of a substance are vibrating. Units typically degrees C or degrees K (0K = -273C)
Precipitation - water that falls from sky (rain, hail, snow). Units either mm or depth of snow.
Wind - movement of air as a result of pressure or density gradients. Units usually ms^-1
Pressure; force exerted on a column of air. Units; Pascals.
Humidity; moisture content of air. Measured in several ways, most commonly relative humidity.
Solar radiation. Measured as either hours per day or intensity of sunlight - watts per square meter or mega joules per square meter per day.
Clouds; condensed water droplets or ice. Units - oktas - 8ths of sky covered.
Atmosphere. Where weather occurs. Regulates energy of Earth lost and gained. Without it the temperature would be -18C. Linked to biosphere (Gaia etc.) Mainly made up of N2 and O2 - 99%. Argon 0.9%. Trace gasses the remainder. CO2 is now 0.04%.
Structure is divided in three different ways. By composition, temperature and function.
Composition; Homosphere - 0-80km. Gasses mixed. Heterosphere - 80km-480km. Gasses stratified by molecular mass. Heterosphere represents 0.001% of atmosphere by mass.
Temperature; Troposphere - 0-18km. Temperature drops with altitude. 90% of atmosphere by mass. Stratosphere - 18-50km. Temperature increases with altitude. Temperature inversion. Mesosphere 50-80km. Temp drops with altitude. to -90C. Thermosphere. Corresponds with heterosphere. Temperature increases with altitude 80-480km.
Function - Ionosphere 50-480km. Absorbs cosmic, gamma and xrays. Ozonosphere - Concentrated O3 in stratosphere. Absorbs ultraviolet. Thinnest at poles and damaged by cfcs.
Weather is the state of the atmosphere at a given place and time. It provides raw observations and is associated with instantaneous measurements of conditions. It is described by climatologists.
Climate is the generalisation of weather data over long periods of time. In a typical weather environment you get average conditions plus variation. Climate tries to explain them. Climate is what you expect, weather is what you get.
Scale is very important for climate and weather. Macroscale, mesoscale and microscale. Looking at things from a global scale to a continent scale to a local scale.
Typically the macroscale is dominated by horizontal movement. The microscale is dominate by vertical movement and the mesoscale is a mix of both. Scale in time is also important - diurnal time (day night), ENSO, solar cycles etc. Some of these are regular and some are irregular.
Earth's climate system can be broken in to many parts - atmosphere, hydrosphere, biosphere, cryosphere (ice), and lithosphere. There are also many feedbacks
Some definitions;
Temperature ; rate at which molecules of a substance are vibrating. Units typically degrees C or degrees K (0K = -273C)
Precipitation - water that falls from sky (rain, hail, snow). Units either mm or depth of snow.
Wind - movement of air as a result of pressure or density gradients. Units usually ms^-1
Pressure; force exerted on a column of air. Units; Pascals.
Humidity; moisture content of air. Measured in several ways, most commonly relative humidity.
Solar radiation. Measured as either hours per day or intensity of sunlight - watts per square meter or mega joules per square meter per day.
Clouds; condensed water droplets or ice. Units - oktas - 8ths of sky covered.
Atmosphere. Where weather occurs. Regulates energy of Earth lost and gained. Without it the temperature would be -18C. Linked to biosphere (Gaia etc.) Mainly made up of N2 and O2 - 99%. Argon 0.9%. Trace gasses the remainder. CO2 is now 0.04%.
Structure is divided in three different ways. By composition, temperature and function.
Composition; Homosphere - 0-80km. Gasses mixed. Heterosphere - 80km-480km. Gasses stratified by molecular mass. Heterosphere represents 0.001% of atmosphere by mass.
Temperature; Troposphere - 0-18km. Temperature drops with altitude. 90% of atmosphere by mass. Stratosphere - 18-50km. Temperature increases with altitude. Temperature inversion. Mesosphere 50-80km. Temp drops with altitude. to -90C. Thermosphere. Corresponds with heterosphere. Temperature increases with altitude 80-480km.
Function - Ionosphere 50-480km. Absorbs cosmic, gamma and xrays. Ozonosphere - Concentrated O3 in stratosphere. Absorbs ultraviolet. Thinnest at poles and damaged by cfcs.
Climate lectures 2 and 3
Energy and radiation
Definitions;
Forces;
Acceleration = change in velocity over change in time.
Force=mass x acceleration
Work=force x distance
Energy is the capacity to do work.
Pressure = force /area
atmospheric pressure is force due to gravity x mass of air/area.
Air pressure dramatically decreases with hight - follows an exponential looking curve. Air is compressible while water is not.
Energy - there are 4 major forms
Radiant - electromagnetic etc. from sun.
thermal - sensible and latent heat.
potential
kinetic - movement
Energy is always being converted around these forms.
Sun is hot (ORLY). Source of electromagnetic radiation. Typically 0.15 to 3 micro metres is solar radiation while 3 to 100 micro metres wave length is terrestrial radiation. All objects with a temperature above - 0K emit electromagnetic radiation. Solar radiation is mainly ultraviolet 9%, visible light - 45% and infrared 46%
Radiation laws - thermodynamics etc.
Power; energy usage over time (also flux). Units; joules per second or watts
Irradiance or radient flux density - energy flux per unit area through which it passes.
Black body - a body that absorbs all energy incident upon it of the wavelength and temperature considered - a perfect absorber and emitter.
Emissivity - fraction of energy emitted by a natural material to that emitted by a black body at the same temperature for a given wave length
Absorptivity - fraction of energy absorbed by a natural material compared to that absorbed by a black body at the same temperature for a given wave length.
Radiation laws
The emissivity is the same as the absorptivity for a given object at the same temperature and wave length.
Plank's law (not on exam) - calculates the amount of energy radiated by a black body for a given wave length and temperature.
Wein's displacement law - calculates the wavelength of the maximum emission for a black body at a given temperature.
The Stefan Boltzmann law - radiant energy from an object is a function of the 4th power of the temperature in K.
Solar constant is the amount of radiation from the sun that reaches the upper atmosphere of the Earth of all wavelengths per unit of time per area. Energy at a particular place and time is controlled by the Earths orbit and rotation.
The amount of energy received at a given time varies because the distance from the Earth to the sun varies.
Solar zenith angle is the angle from the sun from straight up.
Solar declination is the latitude where the solar zenith is 0. - moving around the equator.
The biggest factor on solar radiation in the atmosphere is cloud. It depends on thickness, solar zenith, and size distribution and amount of water and ice in cloud.
Absorption - radiation passing through gasses results in some being converted to heat. This depends on gas and wavelength. Greenhouse gasses are particularly good at absorbing particular wave lengths.
The atmospheric window is a gap in wavelengths absorbed by gasses meaning that it escapes.
Scattering - is when radiation is redirected by a particle of matter in the way of the radiation. When atmospheric gases are smaller than the wavelengths of light then it is more likely to be scattered. Hence more blue is scattered than red, and the sky is blue.
Reflection is when the radiation completely changes direction. Albedo is reflection.
Energy and radiation
Definitions;
Forces;
Acceleration = change in velocity over change in time.
Force=mass x acceleration
Work=force x distance
Energy is the capacity to do work.
Pressure = force /area
atmospheric pressure is force due to gravity x mass of air/area.
Air pressure dramatically decreases with hight - follows an exponential looking curve. Air is compressible while water is not.
Energy - there are 4 major forms
Radiant - electromagnetic etc. from sun.
thermal - sensible and latent heat.
potential
kinetic - movement
Energy is always being converted around these forms.
Sun is hot (ORLY). Source of electromagnetic radiation. Typically 0.15 to 3 micro metres is solar radiation while 3 to 100 micro metres wave length is terrestrial radiation. All objects with a temperature above - 0K emit electromagnetic radiation. Solar radiation is mainly ultraviolet 9%, visible light - 45% and infrared 46%
Radiation laws - thermodynamics etc.
Power; energy usage over time (also flux). Units; joules per second or watts
Irradiance or radient flux density - energy flux per unit area through which it passes.
Black body - a body that absorbs all energy incident upon it of the wavelength and temperature considered - a perfect absorber and emitter.
Emissivity - fraction of energy emitted by a natural material to that emitted by a black body at the same temperature for a given wave length
Absorptivity - fraction of energy absorbed by a natural material compared to that absorbed by a black body at the same temperature for a given wave length.
Radiation laws
The emissivity is the same as the absorptivity for a given object at the same temperature and wave length.
Plank's law (not on exam) - calculates the amount of energy radiated by a black body for a given wave length and temperature.
Wein's displacement law - calculates the wavelength of the maximum emission for a black body at a given temperature.
The Stefan Boltzmann law - radiant energy from an object is a function of the 4th power of the temperature in K.
Solar constant is the amount of radiation from the sun that reaches the upper atmosphere of the Earth of all wavelengths per unit of time per area. Energy at a particular place and time is controlled by the Earths orbit and rotation.
The amount of energy received at a given time varies because the distance from the Earth to the sun varies.
Solar zenith angle is the angle from the sun from straight up.
Solar declination is the latitude where the solar zenith is 0. - moving around the equator.
The biggest factor on solar radiation in the atmosphere is cloud. It depends on thickness, solar zenith, and size distribution and amount of water and ice in cloud.
Absorption - radiation passing through gasses results in some being converted to heat. This depends on gas and wavelength. Greenhouse gasses are particularly good at absorbing particular wave lengths.
The atmospheric window is a gap in wavelengths absorbed by gasses meaning that it escapes.
Scattering - is when radiation is redirected by a particle of matter in the way of the radiation. When atmospheric gases are smaller than the wavelengths of light then it is more likely to be scattered. Hence more blue is scattered than red, and the sky is blue.
Reflection is when the radiation completely changes direction. Albedo is reflection.
