Transcript Geology and Climate Glaciers, Deserts, and Global Climate

Chapter 9
Ice and Glaciers, Wind and Deserts
•Solar heat drives evaporation, makes precipitation,
and generates glaciers. Differential solar heating
of land, water, and thus air makes the winds
•Glaciers shape our landscape and stand for a large
reserve of fresh water
•Wind is not a serious hazard except the winds during
severe storms. Winds also shape the earth’s
surface, but not so efficient
Glaciers – a mass of ice that moves over the land under
its own weight and shape the land
Excellent indicator for global climate conditions
(warm or cool). Not be developed in a single winter
Glacier Formation
Heat from the sun is generally constant
Climate factors may influence the global temperature budget
Global cooling – ice will accumulate and build ice sheets & glaciers
Global warming – ice sheet retreat and glaciers get smaller
Factors that change climate include – composition of the
atmosphere, pollution or particles suspended in the
atmosphere, abnormal heat retention (or loss) from
the oceans
**There must be sufficient moisture in the air,
and thus the necessary precipitation
1.The amount of winter snowfall must exceed summer melting
2. Snow accumulates during cold periods
3. Snow transforms to ice
4. Overlying ice will pack the ice tighter and thicker
5. Packing causes the ice to re-crystallize into a denser ice called firn
6. Gravity will pull the thickened mass of ice down any slope
Types of Glaciers – based on size and occurrence
1. Alpine Glaciers – (also known as mountain or valley
glaciers) occur at high altitude (cooler temperatures)
2. Continental Glaciers – (also known as ice caps or ice
sheets) occur near the poles (over land); they are larger
and rarer
 Glaciers flow as plastic ice masses and at different
rates;( overall movement is down slope)
 Movement is slow at the base of a glacier where it is
in contact with and scrapes the valley walls
 Faster Movement higher in the glacier
 Glacier movement has a terminus
 Glacier that encounter water will experience calving
 Temperatures at the terminus are warm and evaporation,
or melting, removes ice - ablation occurs
 At one place on the glacier an equilibrium line is established
 Above it snow accumulates
 Below it ice ablation occurs
 Overall glacial movement is slow and steady
(a few tens of meters per year);
surges are possible (several tens of meters per day)
 Glacier Erosion – very effective process
 Large mass and solidity of a glacier will shape the surface of
the earth
 Sediments are picked up and carried off –
abrasions and striations are left behind
 Carves its own valley. U shaped valleys mark locations
where alpine glaciers once stood
 Glacier Deposition – abundant material is transported
on or along the sides of glaciers: a variety of moraines will form
 Drift: formed by till
 Outwash: is deposited at the terminus of a glacier
 Important freshwater source
 Approximately 75 % of fresh water is stored as glacial ice
 Glacial meltwater may be the principal source of
summer streamflow in the regions having glaciers
 Overall volume of glacial ice can be manipulated
 Cloud seeding activities in glacial areas may cause
accumulation of increased amounts of ice
 Dusting glaciers with black coal may cause an increase
melt of glacial ice to occur
 Wind is moving air, air moves in response to variations
in air pressure
 Wind accounts for a minor amount of sediment erosion and
transport; but regionally it is very important
 Wind erosion consists of abrasion, forming ventifacts,
or deflation, forming desert pavement
 Vegetation is critical to reducing the effects of wind erosion
 Wind Deposition – principal feature of wind deposition
is the sand dune
 Dune Migration will occur if wind blows from
predominately a single direction
 Wind generally does not move sand or coarser
particles very rapidly
 Fine dust, or silt, can be carried off long distances by
the wind and is deposited as loess
 Loess can originate in either desert or glacial areas
 Loess, once deposited forms a porous and open structure;
holds abundant water
 Loess does not make a good foundation material –
hydrocompaction may cause cracks to
form in foundations or structures
 Structures may also settle unevenly or collapse
Deserts – regions with limited precipitation, people, and
vegetation. (The features of wind processes are observed)
 Causes of Natural Deserts
 Found about 30o Latitude (north or south);
 dry descending and warm air masses
 Warm and dry air can hold abundant water; evaporation rates are high
 Topography and prevailing wind patterns establish rain shadow;
moisture extracted on windward slopes of mountain ranges
 Process: Air mass is cool and dry at maintain tops,
it warms as it descends on leeward side of mountain
 Causes of Desertification
1. Rapid development of desert-like conditions caused by human
activity
2. Major and repeated disturbance to vegetation without complete
recovery
3. Overuse of regional surface and ground water resources