Geology and Climate Glaciers, Deserts, and Global Climate Trends Chapter 9 Solar heat drives...

Geology and Climate

Glaciers, Deserts, and Global Climate Trends

Chapter 9

•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•Global climate changes can occur significantly over a long term

Glaciers and Glacial Features• 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

and 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

Figure 9.2

Glacier Formation• There must be sufficient moisture in the air, and

thus the necessary precipitation• The amount of winter snowfall must exceed

summer melting• Snow accumulates during cold periods

– Snow transforms to ice– Overlying ice will pack the ice tighter and thicker– Packing causes the ice to recrystallize into a denser ice called firn

– Gravity will pull the thickened mass of ice down any slope

• Types of Glaciers – based on size and occurrence– Alpine Glaciers – (also known as mountain or valley glaciers)

occur at high altitude (cooler temperatures)– Continental Glaciers – (also known as ice caps or ice sheets)

occur near the poles (over land); they are larger and rarer

Figure 9.3

Figure 9.4

Movement and Change of Glaciers• 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• Movement higher in the glacier is faster• 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)

Figure 9.5

Figure 9.6

Figure 9.7

Glacial Erosion and Deposition• 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 and outwash, is deposited

at the terminus of a glacier

Figure 9.8

Figure 9.9

Figures 9.10 a, b, and c

Figures 9.12 a and b

Glaciers as a water source

• 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 and its Geologic Impacts• 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– Particles of sand will move by rolling, or saltation, up the

shallower windward dune face– Once at the dune top they fall down the steeper slip face

Figure 9.13

Figures 9.14 a and b

Figures 9.15 a and b

Figure 9.16

Figures 9.17 a and b

Figures 9.18 a and b

Figure 9.19

Wind and its Geologic Impacts

• 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

Figure 9.20

Figure 9.21

Deserts and Desertification• 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

• Air mass is cool and dry at maintain tops, it warms as it descends on leeward side of mountain

• Causes of Desertification– Rapid development of desert-like conditions caused by human

activity– Major and repeated disturbance to vegetation without complete

recovery– Overuse of regional surface and ground water resources

Figure 9.22

Figure 9.23

Figure 9.24

Global ClimatePast and Present

• Evidence of Climates Past– Study geologic (rock and sediment )record– Recent changes in soil and vegetation distribution– Oxygen isotopes (18O/16O) in shell material

• Ice Ages and their Possible Causes– Changes in solar out put of energy– Disruption to global wind or ocean circulation patterns– Atmospheric phenomena blocking incoming solar

radiation• Volcanic eruptions of ash• Increase in cloud cover• Change in chemical composition of atmosphere

Figures 9.25 a and b

Figure 9.26

Figure 9.27

Figures 9.28 a, b, and c

Figure 9.29

Figure 9.30

ClimatePresent and Future

• The Greenhouse Effect involves sun light (energy) entering the atmosphere and a component of the atmosphere (CO2) trapping radiant heat (infrared energy)

• The result is warming of the atmosphere and Global Warming

• Increases, or decreases, in the concentration of CO2 in the atmosphere will show a respective increase, or decrease, in global warming

Figure 9.31

Figure 9.32

Figure 9.33

Figure 9.36

ClimatePresent and Future

• Several centuries ago human activity did not adversely affect the CO2 balance of the atmosphere

• The industrial revolution has placed about 30 % additional CO2 into the atmosphere– Global warming has occurred

• This trend must be changed or we will suffer consequences– Rise in sea level; about 20 % of current land area

would be submerged– Progressive expansion of marginal agricultural lands– Increase in severity of storm distribution and activity

Figure 9.37

ClimatePresent and Future

• Other greenhouse gases include methane (CH4), nitrous oxide (NO2), CFCs, and plus others– These gases are becoming more concentrated in our

atmosphere also

• Global cooling apparently can be promoted by an increase of SO4 from volcanic eruptions (plus abundant ash and clouds)– To achieve a balance in global warming and cooling a

reduction to the input of greenhouse gases and increase in the concentration of volcanic SO4 would be necessary

• How can this be done? Should it be done?

Figure 9.38

Winds and CurrentsClimate and Commerce – El Niño

• The interplay between atmosphere and oceans is complex– Oceans are sinks for CO2 – Generally, only the upper most part (within 100-200 meters of

the surface) of the oceans interact with the atmosphere• Directional shifts in wind direction will disrupt ocean circulation

patterns• Shifts in ocean circulation patterns will cause normal upwelling

cold, deep, nutrient rich water to cease• Shifts in the distribution of flora and fauna will occur

– Fishing industries must shift their operations

• El Niño (Southern Oscillation) is such a cyclic warm event occurring every four to seven years when warm waters from the western South Pacific extend eastward to South America– La Niña (a cold event) is the opposite and cycles periodically also

• The Pacific Decadal Oscillation (PDO) is a cycle of fluctuation surface temperature patterns that occur over a 20-30 year period

Figure 9.39

Figures 9.40 a and b