Chapter 6 Flashcards
What is the basic definition of glaciers
- it is a mass of relatively slow moving ice
- > created by the long term accumulation of snow
- in mountain regions, glaciers form whenever snow accumulation during the winter exceeds that which is removed by melting during the summer
- > the weight of accumulating residual snow eventually begins to convert the lower layers to ice as it is compressed and made denser
Describe the specifics of how glaciers form
- compaction of the surviving snow under a mass of new snow
- > this compaction causes the expulsion of air bubbles within the buried layers
- after about two winters, residual snow turns into firn
- > firn is an intermediate state between snow and glacier ice
- > this usually occurs once its density is around 400 kilograms per cubic meter
- when the firn density reaches 600 to 700 kg per cubic meter
- > any air that hasn’t been squeezed out is now trapped as bubbles as the snow pack is sealed off
- > firn becomes glacial ice when its density hits around 850 kg per cubic meter
- > any remaining air bubbles are isolated from one another and locked into the ice
What is the color of firn
-if it has a whitish color
What is the color of glacial ice
-if it has a bluish color
What are the shapes of the snow crystals
- very complex shapes with intricate arms or branches when they fall from the sky
- > once on the ground, they come into contact with one another
- > once they connect, there are pore spaces left between them
Where does melting first occur in crystals
- it occurs at the contact point between each snow crystal
- >melt water flows into the spaces between the crystals where the pressure is lower and the freezing point is higher
What is the process of sintering
- when melt water flows into the spaces between the crystals where the pressure is lower and the freezing point is higher
- > here water refreezes
- > binds snow crystals together and enlarges individual grains
- > with time and increased pressure, snow crystals tend to slowly interlock with each other and grow in size
How does snow to glacier ice form in dry snow zones
- in dry snow zones, there is rarely any melting
- > it is too cold for melting
- instead there is the mechanical breakdown of snow crystals as they’re blown by the wind
- > they are broken into smaller rounder, grains
- > smaller, rounder grains pack together more efficiently
What are the largest glaciers on the planet known as
- they are known as ice sheets
- > they are found only in Antarctica and Greenland
- note an ice sheet is a massive glacial land ice extending more than 50,000 square kilometres
- > their flow is completely independent of the topography beneath
What mountains are the east and west Antarctic ice sheets separated by
- they are separated by the Transantarctic mountains
- >but these mountains are almost completely buried by ice
What are iceacaps
- they are miniature ice sheets covering less than 50,000 square kilometers
- > they form primarily in the polar and sub-polar regions that are high in elevations
Are icecaps constrained by topographical features
- no
- > they lie over the top of mountains
- > dome of an icecap is usually centered on the highest point of the massif
- > ice flows away from this high point which is called the ice divide towards the icecap’s periphery
Are mountain glaciers confined to the topography of the landscape
- yes
- > unlike ice sheets or icecaps
- > the largest type of mountain glacier is an icefield
What is the difference between an ice cap and an icefield
Icefield
- > the flow of an icefield is constrained by the underlying topographic features
- > eg; Columbia Icefield in the southern part of Jasper National Park
Valley glaciers
- glaciers expanding from an icefield
- they are sometimes referred to as outlet glaciers
- can be very long
What is piedmont glacier
- occur when steep valley glaciers spill into a relatively flat plain
- > they fan out into bulblike lobes
- > eg; Malaspina Glacier in southeastern Alaska
What are tidewater glaciers
- they are valley glaciers
- > that flow far enough to reach into the sea
- > eg; Columbia Glacier in the Chugach Mountains
- as the ice reaches the sea
- > pieces break off, forming small icebergs
What are hanging glaciers
- when a major valley glacier system retreats and thins
- > tributary glaciers are left in smaller valleys high above the shrunken central glacier’s surface
-note these glaciers often terminate at or near the tops of cliff bands
What are circue glaciers
- much smaller than valley glaciers
- named for the isolated bowl-like hollows or basins they occupy(cirques)
- they are typically found high on mountainsides and tend to be wider rather than longer
- its survival requires snow deposited by avalanches from the surrounding rock walls
- > walls also provide the glacier with some shade
- > greatly reducing the direct solar radiation and limiting melting
- > shading also limits the size of these glaciers, constraining the glacier to the shaded area
How is material from a glacier removed
- through surface melting, evaporation and glacier calving
- material added is annual input and material removed annual output
How is mass balance calculated? What does it mean to have positive mass balance vs negative mass balance
- annual input-annual output
- positive mass balance=glaciel advance
- negative mass balance=glacier shrinkage
- steady state=glacier remains approximately the same size
What is the accumulation zone and the ablation zone
Accumulation
- > snowfall is greatest at the highest point in the glacier where it is the coldest
- > here the annual input exceeds the output
Ablation
- > output in the form of evaporation and melting exceeds the inputs
- > here the annual mass balance is negative
What is the area between the accumulation zone and the ablation zone
- area of equilibrium
- > it is the equilibrium line altitude
- > where conditions favor glacial advancement, the ELA is low
- > where conditions favor glacial retreat, the ELA is high
What would happen if the glacier could not move
- because of accumulation, the area above would get thicker and area below would get thinner
- > the terminus would end up retreating further
Who was the first one to record the observations that glaciers flowed
- sveinn Palssen in 1794
- > observed bow-shaped bands that are known as ogives
- > he predicted that ice has some fluidity without actually melting
What is the main reason glaciers flow
- they flow due to gravity
- >the downward flow causes the ice to deform and flow downwards
Are glaciers continually changing in surface area, shape, and slope over time
-yes
Does ice flow towards the terminus
- yes
- >the terminus position is moving back but the ice still moves down to the terminus
What is basal sliding
- slippage of ice over mass of rock
- >leaves striations on bedrocks below
How does basal sliding
- temperature of ice at the base
- presence of water to serve as lubricant
Does balar sliding occur in polar regions
- no
- > since ice is frozen to the bedrock layer
- in other regions, where the temperature is higher and there is water on the basal surface
- > basal sliding is more pronounced
What is bed deformation
- ice is carried over time like a deforming carpet
- flow rates due to ice deformation is constant
- > it is due to gravity, ice thickness and slope angle
- > but introducing water to this equation varies the flow rate greatly
- > it isn’t just about these three factors anymore
What is the Little Ice Age
- it lasted from 1500 to 1850
- > it was a short period of time
- > a window when most of the world’s glaciers were actually advancing
- > there was a great cultural shift in our understanding of glaciers and ice
What are crevasses and why do they form
Crevasses
- > deep cracks or fractures found in the glacier
- > as opposed to crevices which form in rocks
- they form due to tension stress
- > so their distribution, size and arrangement provide useful information on the flow behavior of ice
Do crevasses occur most often when the middle and the sides of the glacier move at different rates?
- yes
- > especially when ice curves around a bend
- > or where the slope steeps and the rate of movement increases
Are crevasses transverse or horizontal to the direction of flow?
- yes
- >but they can be oriented really in any direction
Are crevasses largely restricted to the surface
- yes
- >where the ice is much more brittle and fractures more easily than down lower
How does the presence of crevasses benefit glaciers
- it increases the efficiency of rock transport
- rock debris that falls into crevasses becomes incorporated into the glacier
- > often not seen again until the glacier releases the material at the terminus
- they also hasten ablation by increasing the glacier’s surface area
- > by the pooling of melt water and by the disaggregating the ice near the terminus
How do you protect yourself against crevasses when travelling over glaciers
- when traveling over glaciers
- > experiences mountaineers protect themselves with ropes and with harnesses
- > they also regularly practice crevasse rescue scenarios and hire professional mountain guides
What is a moraine
- it is the linear accumulation of rocky debris oriented in the direction of the flow
- > they are created when the glacier pushes or carries rocky debris as it moves
hat are lateral moraines
- vertical partitions between two ice masses
- >incorporated into the glacier
Does the presence of moraines alter the mass balance
- since the rock material is dark in color and can absorb more solar radiation
- > so yes it does affect it
Are glacial valleys trough shaped
- yes
- >they are the most visible glaciated landforms
Is there a glaciated valley in Yosemite National park
-yes
What are aretes and horns
Aretes
- > jagged narrow ridges where the backwall of two glaciers meet
- > erode the ridge on both sides
Horns
->when glaciers erode the mountain to the point where a steep point is left on the top
