Lecture 16 - A World of Changing Environments

Question 1

Define Creep when referring to Glacial Flow

Answer 1

-Occurs when firn is turned into ice under pressure
-Ice crystals have parallel cleavage planes and tend to split in one direction
-Under pressure at depth, they align parallel to the stress and slide past each other
-This causes down-slope glacier flow

Question 2

Define Fracture when referring to Glacial Flow

Answer 2

-Occurs when stress placed on ice cannot be accommodated by deformation so ice forms crevasses
-Occurs mainly in the brittle zone near the surface but can extend deeper

Question 3

Define Basal Flow and Deformation for Glacial Flow

Answer 3

-Both require water at the ice/bed interface
-Ice slide over saturated sediment and this sediment deforms like plasticine
-Sediments slide over a layer of high-pressure water

Question 4

Define Abrasion

Answer 4

-Occurs under thick ice
-Requires debris-rich ice which acts like sandpaper
-Produces fine-grained sediment and streamlined forms

Question 5

Define Quarrying/Plucking

Answer 5

-Occurs under thinner ice
-Requires fluctuating water pressure at the bed
-‘Ripping’ effect produced boulders/blocks and stepped features in the bedrock (depending on the weakness and structure of the bedrock)

Question 6

Where can Debris flow in a Glacier?

Answer 6

-Supraglacial = on top of glacier
-Englacial = in the glacier
-Subglacial = below the glacier
-Proglacial = in front of glacier (this often involves a meltwater-dominated environment)

Question 7

Difference between Morainic and Glaciofluvial Landforms

Answer 7

-Morainic = created in direct contact with the glacial ice
-Glaciofluvial = created in connection to melt-water

Question 8

What is an Esker?

Answer 8

-A ridge-shaped inversion feature which is evidence of previous negative space like a channel in the ice
-A cast of a subglacial river
-Forms by the channel filling up with sediment composed of sand and gravel

Question 9

What is a Kame Terrace?

Answer 9

-Inversion feature which is evidence of water at the edge of an ice mass
-Fine-grained sediments and debris flows are deposited in standing water
-Often form flat-topped mounds as they are levelled out by deposition into the water

Question 10

What are Outwash Plains/ Sandurs?

Answer 10

-Dynamic braided rivers
-Flat, low angle sloping away from the glacier
-Sand and gravel deposition