Chapter 9: Ice and Glaciers, Wind and Deserts Flashcards
Glaciers
Masses of ice that move under their own weight, under the force of gravity. Typically form at high latitudes and/or high altitudes.
How long does it take for glaciers to form?
can take several centuries to form (and melt)
What conditions must be met for glaciers to form?
1) precipitation
2) a higher rate of snowfall than melt each year (allows glaciers to grow)
3) mountains (higher elevation → colder temperatures)
4) gentle slope
Transformation of snow to glacier ice
A slow process that can take decades or thousands of years in which loose snow (90% air) compacts and become denser as air is driven out, and turns into firn. Then eventually recrystallizes to form glacial ice, which consists of interlocking ice crystals. Eventually gravity pulls the mass of ice downslope, creating a glacier.
Alpine Glacier
numerous today also called mountain or valley glaciers, occurs at high altitudes
Continental Glacier
Larger glaciers which are rarer today, typically occur near poles. can span entire continents and reach large thicknesses.
How many continental glaciers exist today and where are they?
two main continental glaciers remain in present day
1) Greenland
2) Antarctic ice sheets
Pleistocene Ice Age and Glaciers
During this time (2.5 Ma - 11,700 years ago) much of the northern hemisphere was covered in glaciers.
Plastic Deformation
occurs at depths of 60 m in a glacier, ice grains change shape very slowly as the glacier moves, and/or new grains grow while old ones disappear.
Crevasses
the cracks, when ice is too brittle to flow, and instead moves by cracking
What depth does ice stop cracking?
ice does not crack below depths of 60 m: the 60 m boundary is the brittle-plastic transition
Basal Sliding
the presence of liquid water or a wet slurry may appear beneath a glacier, reducing friction, and allowing the glacier to glide along the equivalent of a wet cushion of water.
Why do glaciers move?
glaciers move due to gravity: glaciers flow in the direction in which their top surface slopes. Glaciers flow between 10-300 m/year
Zone of accumulation
snowfall adds ice to a glacier
Zone of Ablation
Ablation is the removal of ice
if temperatures at the terminus are warm, evaporation, or melting
Three processes of zone of ablation
Sublimation, melting, calving
Sublimation
evaporation of ice into water vapor
Melting
transformation of ice into water
Calving
breaking off of chunks of ice at the end of the glacier into smaller pieces
Equilibrium line
The boundary between the zone of accumulation and the zone of ablation and defines whether a glacier grows or shrinks.
Toe of glacier
The part of the glacier that advances - its leading edge
Glacial Advance vs. Glacial Retreat
Advance glacier grows, retreat glacier shrinks
Glacial Erosion and Deposition
glaciers can carve relief into mountainsides: their movement strips away topsoil and scrapes and scours the underlying bedrock as they travel over the surface of a continent
V-shaped and U-shaped valleys
A V-shaped valley is carved out by a stream and U-shaped valleys are when glaciers erode and widen the sides of the valley and also its floor
Glacial striations
the grooves/scratches in rocks left due to glacial activity, they form parallel to the flow direction of the glacier
What does plucking refer to?
as a glacier moves it plucks parts of the neighboring mountainside
Landforms on mountains (3)
Cirque: bowl-shaped depression that develops on the side of the mountain at the head of a glacier
Arête: knife-edge ridge of rock that separates two adjacent cirques
Horn: pointed mountain peak surrounded by at least three cirques
Till
sediment transported by ice and deposited beneath, at the side, or at the toe of a glacier. The sediment is usually poorly sorted compared to stream-deposited sediment: glacial ice can carry clasts of all sizes.
Outwash
When till mixes with meltwater
Moraine
A pile of rock and dirt. The term is used to describe debris piles carried or left behind by glaciers
Lateral Moraine
the side edge of the glacier, where two valley glaciers merge, the debris in the two lateral moraines merge to become a medial moraine
Medial Moraine
often seen as a stripe running down the composite glacier
End Moraine
The sediment that accumulates at the toe of the glacier (leading front edge).
Terminal Moraine
the debris deposited by the furthest extent of glacial ice
The Rocky Mountains
many of its peaks and valleys were glacially carved (from the midwest extending all the way to the west coast)
The Great Lakes
the lakes occupy basins carved and deepened by glaciers and filled with glacial meltwater
Canada’s Hudson Bay
is a depression formed by the weight of the ice sheets and flooded with seawater after the ice melted away
The drainage of the Mississippi river
In part was formed by meltwater from retreating ice sheets. the sediments carried along with that meltwater are in part responsible for the fertility of the Midwestern farmland, and supply the groundwater tapped today for irrigation.
How many ice ages have happened in the past billion years? Which was the most recent?
5 major ice ages in Earth’s history, the most recent took place during the Pleistocene Epoch
Interglacial period
the time between when glaciers retreat and advance
What geologic epoch are we in?
the Holocene, we are considered to be in an interglacial period because the glaciers are still present (though rapidly retreating)
Milankovitch Cycles
looks at the change in the shape of the Earth’s orbit, tilt, and wobble of the Earth’s axis over time
How is wind created?
Wind is created in response to differences in air pressure, which is related to air temperature. The surface of the Earth is heated more near the equator, less at the poles, causing the equatorial air to rise up into the atmosphere and move toward the poles, and the cooler polar air sink and move toward the equator, forming a series of convection cells.
Where is wind erosion most effective?
In areas lacking vegetation, e.g., beaches, deserts. Strong winds can sandblast terrains and rocks creating ventifacts
Ventifacts
stones with wind-abraded surfaces
Deflation
removal of loose sediment by wind
This lowers the land surface via erosion, and can result in the loss of soil.
Wind Deposition
this creates dunes, usually made of sand, but snow is also possible. The orientation of the dunes reflects the prevailing wind direction, which is the shallower slope side facing upward.
Dune Migration
if there is a strong enough prevailing wind direction, a dune can migrate: its particles get blown up the side of one shallower surface and slide down the steep slip face.
How do crossbeds develop in the dune?
slanted ones develop as layer upon layer of sediment slides down the slip face
Where are deserts found?
deserts are found at all latitudes: the largest are subtropical but deserts can also be found at the poles.
What are causes of natural deserts?
High surface temperatures and topography
How does high surface temperatures cause a natural desert?
The sinking cool air at 30 degrees north and south of the equator results in desert environments due to the cooler air warming as it reaches the surface, taking with it much of the moisture, and causing rapid evaporation.
How does topography cause a natural desert?
Mountain ranges that lie in the path of air currents may push the air to high altitudes as the air rises over the range, causing the air to cool and for it to lose its moisture. As a result, one side of the mountain range is extremely wet, but the opposite side is dry, as the now dry air forms a rain shadow.
Rain Shadow
Moisture extracted on windward slopes of mountain ranges established by Topography and prevailing wind patterns
Desertification
the rapid development of deserts is caused by the impact of human activities, usually as a consequence of land-use practices.
Dust Bowl Desertification
in the 1930s the US Midwest as a result of decades of misguided farming practices caused the topsoil to erode away. Removing native vegetation and replacing them with crops leaves the land vulnerable to degradation during drier conditions.
How does desertification impact food?
it reduces the amount of arable land on which the world depends for food.
