Mountain glaciers and climate change Flashcards
What are two hazards associated with mountain glaciers?
Avalanches
Outburst floods
What two resources do mountain glaciers provide?
Water
Minerals
What do glaciers show the impacts of?
Increasing air temperatures
How is ice formed?
Snow compacts to form ice
Why does snow compact?
Due to the weight of humans or the snow itself
In which direction does the ice in a glacier move?
It moves from the accumulation zone to the ablation zone
What happens when ice reaches the ablation area?
It melts
What can break off glaciers?
Icebergs
What are two ways in which mass balance can be measured?
By direct measurement or remote sensing
What are two forms of direct mass balance measurement?
Ablation stakes
Snow pits
How do ablation stakes work?
Drill into the ice and insert a pipe, overtime the ice will melt and the pipe will become more and more visible
What is an issue with ablation stakes?
They are time consuming
How do snow pits work?
Drill into the glacier with a chainsaw and see layers that show accumulation
What are the issues with direct measures of mass balance? (3)
It is difficult to scale up and there are variations in records.
In addition proximity to humans and accessibility is an issue
Why are there variations in records for direct measurement techniques?
Due to money
What is remote sensing?
This means finding out information about something without touching it
Why is remote sensing good?
Can cover large areas
What is an issue with remote sensing?
Compromises in terms of detail
What are 3 remote sensing methods?
Gravitimetry
Elevation change
SMB/D
How does gravitimetry work?
Look for changes in gravity
How does gravitimetry work?
If the density is known, the volume can be caluclated
How does elevation change work?
Use lasers to repeatedly enter the ice surface to get surface elevation changes?
What is SMB?
Surface mass balance
How does SMB work?
How much put in compared to how much out from models and compare to how much ice is coming out from outlet glaciers
For what size of glaciers is remote sensing best?
Large ones
What is SfM?
Structure from motion
What does SfM do?
Take photos and piece them together to make a model of the surface
Why is SfM useful?
Can get detailed info without having to be on the glacier itself
Why are tropical glaciers found in tropical areas?
Relics from past colder climates
Where is the vast majority of tropical glaciers?
The Andes but also high elevations in Indonesia and some (very little in Africa)
What will happen to tropical glaciers?
They will shrink and disappear
What percentage of the tropical glaciers have shrunk since 1970s?
Up to 50% of their surface area has gone since the 1970s
What is precipitation like in the inner tropics?
Similar precipitation all year round
What is precipitation like in the outer tropics?
Dry season May to September
Wet season is October to March
What type of weather is good for glaciers and why?
Wet snowy years
Albedo- more reflective
Why are glaciers in the outer tropics important?
Demand for water is needed all year round so glaciers act as a baseline throughout the wet and dry seasons
What is the mass balance of tropical glaciers due to?
Temperature and precipitation
When does snow and rain fall onto the tropical glaciers?
In the summer
When does melt occur on tropical glaciers?
In the summer
Give a location where debris covered glaciers are present
Himalayas
Where are the rock debris on debris covered glaciers from?
Surrounding hillslopes
What is an added danger as a result of debris on glaciers?
Avalanches and landslides
What features of the debris can have an effect on melting
Colour and packing
What does thick debris do to the ice?
Thick debris insulates the ice and reduces melt
What is the critical thickness?
This is the balance between thick and thin debris
What does a thin layer of debris do to the melt rate?
It increases it
Where on a glacier is melt highest?
Melt is highest at lower elevations
Where on a glacier is melt lowest?
At higher elevations because it is colder
What causes an inverted mass balance?
Melt being higher at lower elevations and lower at higher elevations
In what sort of areas are debris covered glaciers located that could cause risks?
They are at the top of catchments for highly populated areas
What is a feature of debris covered glaciers?
Ponds form on the glacier surface as water collects at the front of the glacier bordered by the moraines
What is are two issues with ponds on the glaciers?
They are dark and therefore increase the melt rate
Lakes can easily burst leading to catastrophic effects
Can sea ice contribute to sea level rise?
No
What is UAV?
Unmanned Aerial Vehicle
What do UAV surveys do?
Map the surface
What do ground penetrating radars do?
They go down through the ice to measure the thickness
Why is it important to know ice thickness?
To know how long the glacier will last
What are ice cliffs?
Areas of ice with string melting
What do moraines show?
Previous extent of the glacier
What are moraines made of?
Unconsolidated, weak sediment
How do glacier lakes burst?
Through moraines
When do glaciers flow?
On longer time scales
In which direction do glaciers flow?
Downhill
From the accumulation zone to the ablation zone
Why do glacial crevasses form?
When the ice flows too quickly and fractures
Where is the fastest ice flow?
In the middle
Why does the ice at the edges and the bottom flow smaller?
Friction
What is the velocity at the top of the glacier?
0
In which direction does the ice in the glacier flow?
Top to bottom
What are 3 methods of ice flow?
Internal deformation
Basal sliding
Deformation of sediment under the glacier
In what type of glacier does internal deformation occur?
All glaciers
What is internal deformation?
Ice deforming under its own weight
How does internal deformation occur?
Ice moves along boundaries of grains and recrystalises
What factors affect the rate of deformation? (5)
Slope
Thickness
Temperature
Water content and crystal properties
What does basal shear stress do?
It drives glacier flow
What is basal shear stress caused by?
Density of ice and gravitational acceleration which are constant
Ice thickness
Ice surface slope
What effect does ice thickness have on the movement of the glacier?
Thicker ice = faster movement- faster deformation
What effect does ice surface slope have on glacier movement?
Steeper slope = faster movement - faster deformation
What is ice thickness?
How much ice there is
What does Glen’s flow law give?
The amount of deformation for a given amount of stress
What is deformation also known as?
Creep
How easily does warm ice deform?
Ice deforms easily when warm
What type of glaciers are polar glaciers?
Cold- based
What type of glaciers are temperate glaciers?
Warm- based
What is PMP?
Pressure Melt Point
What is the melt point dependent on?
Pressure
Temperature
Why can liquid water be present at colder temperatures?
Because of pressure
What is meant by cold-based glaciers?
They don’t reach PMP
What is meant by warm-based glaciers?
They reach PMP
In which type of glacier does basal sliding and sediment deformation occur?
Warm-based glaciers
What are 6 factors that affect the PMP?
Ice thickness Accumulation rate Ice surface temperature Meltwater Geothermal heat Friction
What are polythermal glaciers?
They have some warm ice and some cold ice so some parts are at the PMP but others aren’t
In what two ways can basal sliding occur?
Enhanced basal creep
Regelation
What is enhanced basal creep?
Ice hits an obstacle which increases the stress, causing the ice to deform more quickly around the obstacle
What is regelation?
This involves transfer of heat
Ice heats an obstacle, causing it to melt. Once the obstacle has been overcome, the ice refreezes again
What is sediment deformation?
Material at the bottom of glaciers is weak, watery and unconsolidated which allows the glacier to slide along on top
What is glacial hydrology?
This is the movement of water through the glacier
What is supraglacial water movement?
On top of the glacier e.g.streams
What is englacial water movement?
Within the glacier (through cravasses and moulins)
What is subglacial water movement?
Beneath the glacier
What is proglacial water movement?
In front of the glacier
What does glacial hydrology apply to?
All glaciers
What is sheet flow?
A thin film of water at the bottom of the glacier
What is channelised flow?
Channels of water that remove water efficiently by having an aborescent network
What are the two types of channelised flow?
R channels
N channels
Where are R channels?
Cut up into the ice
Where are the N channels?
In the sediment
What are linked cavities?
These are pockets under the glacier that are linked. Quite inefficient and hard to get the water out
What are canals?
Networks cut down into the rock or sediment under the glacier
Why is glacial hydrology important?
It has an effect on the melt rate and glacial flow
What does the water interact with, making glacial hydrology important?
It interacts with the melt rate
What is warmer, the ice or the water?
The water
For channelised flow, is the effect of the ice or water stronger?
The effect of water is stronger which means that more water melts the ice as it is over a small surface area and causes the ice to expand, this leads to a low pressure
What happens in linked cavities?
Water can’t expand the cavities quickly enough, causing the cavities to raise up and increases the pressure
By how much can cavities raise up?
Cm to M
What effect do linked cavities have on ice flow?
Increased speed of ice flow
