Transcript Glaciers - Novella

Chapter 9
Geology and Climate
Glaciers, Deserts, and Global Climate Trends
•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 Climate
Past 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
Climate
Present 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
Climate
Present 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
Climate
Present 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 Currents
Climate 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