Velocity and Surges

Question 1

What methods are used to measure glacier velocity?

Answer 1

GPS
TLS- terrestrial laser scanning
UAVs
Remote sensing

Question 2

How can TLS be used to measure glacier velocity?

Answer 2

Scan and rescan it at another time and see the differences.

Question 3

What are limitations in using TLS and UAVs to measure glacier velocity?

Answer 3

You need relatively small glaciers

Question 4

What is a benefit of using UAVs to measure glacier velocity?

Answer 4

Detailed velocity measurements

Question 5

What kind of technology can be used for measuring the velocity of larger areas of glaciers?

Answer 5

Remote sensing- SAR (Synthetic Aperture Radar) interferometry

Question 6

How does remote sensing- SAR (Synthetic Aperture Radar) interferometry work?

Answer 6

It is a technique that is used to record the velocity of a glacier by comparing different satellite radar images of the same site.

You need a number of passes over the same location, and then your record the difference

Question 7

Glacier velocity is never constant…but it can be divided into two types.

Answer 7

Continuous

Discontinuous

Question 8

What is a continuous glacier?

Answer 8

One which is travelling at a similar speed most of the time.

Slow- cold based glacier- <30 m/a
Fast- warm based glacier- 50-100 m/a

Question 9

What is a discontinuous glacier?

Answer 9

Discontinuous- change their speed dramatically

Surging glaciers >10,000 m/a
Ice streams >400 m/a

Question 10

What are short term speed up events?

Answer 10

These are usually melt water driven but sometimes tidal driven.
Often called stick slip motion- small thing that happens everyday- Tidal modulated twice per day.

Question 11

What are surges?

Answer 11

Surges are a dramatic glacier advance (Meier and Post, 1969).

They have a long quiescent phase of normal velocity.

…and then a short surge phase glacier 10-10,000 x faster
Period (10-100 years)

Question 12

How much of the worlds glaciers surge?

Answer 12

Less than 1%nworlds glaciers surge (concentrated in certain areas- Alaska, Iceland etc).

Question 13

What is the morphology of a surge?

Answer 13

They have a wave like bulge because the top part of the glacier is flowing so much faster than the lower part of the glacier.

Question 14

How can we tell if a glacier has surged or not?

Answer 14

Amalgamation of features…
Push moraines
Crevasse filled ridges 
Hummocky moraines
Concertina eskers

Question 15

What is a typical surge?

Answer 15

Occur at all scales
Valley glacier
Ice stream in ice sheets

Found both on both rigid and deforming bed glaciers
Both warm and subpolar glaciers

Question 16

Rigid bed model

Answer 16

Short surge cycle- 15 years- 1 year suddenly active- high velocities 40-60 m per day not year

This is because there is a build up of high water pressure in the basal water system.

This leads to increased basal sliding- these cavities become linked and the surge front advances as it destroys the tunnel system, and the higher water pressure makes the cavities.

Question 17

Deforming bed model

Answer 17

The front of the glacier is frozen and the rest is warm based- the surge bulge forms at this boundary.

The subglacial water is flowing through the till

There is a barrier to sliding (frozen toe) stopping the water flowing through the till.

Water pressure builds up and suddenly passes through threshold and glacier shoots forward.

Question 18

Murray et al, 2000, 2003 model

Answer 18

At the start of the cycle, the glacier is cold based (polythermal).

Ice builds up in surge front causing thickening until pmp is reached in part of the glacier- turned into warmbased.

Basal meltwater is produced, which leads to high pore water pressures and weakening of the till.

Accelerated deformation of the till produces frictional heating, more melting, sliding

This causes the ice to thin, causing refreezing and the surge ends.

Question 19

For a glacier to maintain a steady state…?

Answer 19

Mass flux through the system must be in equilibrium with surface mass balance

Energy fluxes must maintain constant enthalpy (ice temperature and water content)

So cold dry glaciers
Small glacier can keep in balance- don’t surge
Larger ones can’t keep in balance- may surge

Question 20

What criterion can be used to distinguish between glaciomarine and glaciotectonic sedimentation?

The glaciomarine environment is dominated by…

Answer 20

sedimentary processes, related to…

Sediment supply
Water content
Distance from the glacier margin.

Question 21

What criterion can be used to distinguish between glaciomarine and

Glaciotectonic deformation, however, is dominated by…

Answer 21

deformational processes, related to…
Effective pressure
Shear strain
Nature of the subglacial material 
Distance from the glacier margin.

Question 22

What are glacio-marine sediments?

Answer 22

Glacio-marine sediments are deposited by glacial metlwater in an ocean environment.

Question 23

What are glaciotectonic landforms?

Answer 23

The surface or morphologic expressions of subsurface structures resulting from glacial deformation of bedrock.

Question 24

In the daily records of surface velocities…
What is base velocity?
What are speed up events?

Answer 24

There is no glacial melt as temperatures are below zero.

Days where the temperature is above zero and melting occurs.

Question 25

What are the models?

Answer 25

Rigid bed model

Deforming bed model

Murray et al, 2000, 2003 model