Earth SC glacial and Arid
What types of deposits are generated by wind?
*Loess* is an extensive accumulation of windblown silt *Dunes* are asymmetrical accumulations of sand saltated by wind
Extent of Ice Age Glaciation
-Last ice age began between 2 and 3 million years ago during the Quaternary Period -Ice sheets and alpine glaciers were far more extensive than they are today -Almost 30% of Earth's land was glacially influenced
How do glaciers erode Earth's surface and what landforms do they create?
-Plucking (picking up large pieces of bedrock) -Abrasion (grinding and polishing bedrock) -Landforms include: glacial troughs, hanging valleys, cirques, arêtes, horns, and fiords
End moraines
-form at the terminus of a glacier (glacial balance in equilibrium)
Medial moraines
-form between two advancing glaciers -Dark stripe of debris within the glacier
Deserts
30% of Earth's land surface is arid Concentrated in subtropics and middle latitudes Affected by many geologic processes Mountain building, running water, wind
Ice sheets
=are found at the poles •Flow out in all directions from a center of snow accumulation •Large scale, obscure underlying terrain
glacier
A glacier is a thick (100s - 1000s of m) mass of ice Originates by accumulation, compaction, and recrystallization of snow Glaciers move slowly because of gravity Accumulate, transport, and deposit sedimen
Wind Erosion: Different from a River
Different from a river Less capable of transporting coarse material Not confined to a channel Relatively insignificant erosional agent
Wind Deposits
Generally two distinctive types: -Extensive blankets of silt from suspended load called *loess* -Mounds and ridges of sand from bed load called *dunes*
Deflation
Lifting and removal of loose material Clay and silt only
Middle-latitude deserts and steppes occur in the *deep interiors of large landmasses*
Little precipitation because of distance to oceans Example of how geologic processes (mountain building) can affect climate
Loess
Loess is windblown silt Tends to erode in vertical cliffs Lacks bedding Deserts and glacial deposits of stratified drift are primary sources of silt
Wind Erosion: similar to a river
Moving air can pick up and transport loose material Similar to a river Velocity of wind increases with height above surface Transports fine particles in suspension and heavier particles as bed load
Saltation
Rolling or skipping of larger particles along the surface
Blowouts
Shallow depressions caused by deflation
Dry climate
Yearly precipitation less than the potential loss of water by evaporation -*Desert* (arid) *Steppe *(semiarid)
Lateral moraines
form along the sides of the valley
Ice shelves
form when glacial ice flows into the ocean •Large, relatively flat •Attached to land and flow outward away from coast •Become thinner seaward
Valley or alpine glaciers
occur in valleys in high mountains Relatively small Advance slowly (a few cm per day) Flow downvalley from an accumulation center Generally width is narrow relative to length
Desert pavement
Stony veneer left behind after deflation removes finer material
African, Arabian, and Australian deserts are a result of* prevailing winds*
Subtropical highs in the lower latitudes Subsiding air is compressed and warmed Creates clear skies and ongoing dryness
sea ice
The Arctic Ocean is covered by *sea ice*(frozen seawater) •Floats •Ranges from a few cm to 4 m thick •Expands and contracts with the seasons
Ground moraines
are gently rolling layers of till deposited as the terminus retreats
Moraines
are layers or ridges of till. the ground sediments being pushed by the glacier forms a ridge.
Ice caps
•Cover uplands and high plateaus •Smaller than ice sheets but bury underlying terrain
Outlet glaciers
•Extend out from ice caps and ice sheets
Piedmont glaciers
•Form in broad lowlands at the base of mountains •Form when glaciers emerge from the confining walls of a valley
Glacial Erosion
•Glaciers erode and transport tremendous volumes of rock •Debris cannot settle out like sediment carried by water or wind •Capable of carrying very large pieces of debris
2) Ice sheets
•Greenland and Antarctica •Extensive ice sheets during the Last Glacial Maximum (~18,000 years ago) •Also covered North America, Europe, and Siberia •Ice sheets have advanced and retreated several times over the last 2.6 million years
