Glacia and Fluvioglacial Processes and the Formation of Associated Features

Question 1

What is the process of lodgement?

Answer 1

Occurs beneath the ice mass when sub-glacial debris becomes stuck on the glacier bed. This occurs when the friction is greater than the drag from the glacier

Question 2

What is the process of Ablation deposition?

Answer 2

Dumping of debris as the glacier thaws and melts

Question 3

What is the process of deformation deposition?

Answer 3

Less common and associated with weak bedrock. The sediment beneath the glacier is deformed by and broken apart by glacier movement

Question 4

What is the process of glacial flow deposition

Answer 4

Occurs if high meltwater causes the debris to creep, slide or flow

Question 5

What are the characteristics of Lodgement till?

Answer 5

Rounded clast, often a matrix of clay or silt.
Forms till sheets and drumlins.
Oriented with the direction of glacier movement.

Question 6

What are the characteristics of ablation till?

Answer 6

Angular and longer .
Unsorted - no orientation

Question 7

What are characteristics of Modified till?

Answer 7

Reworked older deposits - have folds and faults in.
Forms ridges or thin sheets

Question 8

What is fabric analysis?

Answer 8

Analysis on till to understand what type of deposition caused it

Question 9

Generally, how is glacial till deposited?

Answer 9

Unstratified, angular and unsorted.

Question 10

Where can you find moraines?

Answer 10

Sub-glacial or ice-marginal.

Question 11

What is a till plain?

Answer 11

Extensive flat areas of till that cover pre-existing topography up, up to 50m deep. Formed by consistent ablation till dropped as the glacier advances.

Question 12

What are drumlins?

Answer 12

10-50m high, 200-2000km long. The stoss is end up-glacier then sweeps down. Found in lowland areas, and in relatively close proximity to upland centres of ice dispersal.

Question 13

What is the Boulton-Menzies explanation for drumlin formation?

Answer 13

Drumlins are formed by deposition in the lee of a slow-moving obstacle in the deforming layer. The obstacle forms the rock core of the drumlin and moraine is plastered around it.

Question 14

What is the Shaw theory for drumlin formation?

Answer 14

All drumlins are caused by subglacial meltwater in flood, causing irregularities in the bed - formed into drumlins by ice movement. This more explains smaller drumlins.

Question 15

What are the two main sources of meltwater?

Answer 15

Meltwater and basal melting.

Question 16

What are moulins?

Answer 16

A small hole that goes directly down through the ice, formed often by debris on the surface which has melted its way into the ice. Supraglacial streams can seep through it to become englacial or subglacial streams.

Question 17

Where do meltwater streams emerge?

Answer 17

At the snout, through caves called portals.

Question 18

What are the characteristics of fluvioglacial deposits?

Answer 18

Generally smaller as streams can’t carry large till.
Smoother and rounder due to attrition.
Sorted horizontally, larger pieces up-glacier as they require more energy to transport.
Vertically stratified.

Question 19

What is the proximal zone?

Answer 19

Directly ahead of the snout. Largest particle deposits such as moraines.

Question 20

What is the Medial zone?

Answer 20

Further from the ice margin. Meltwater streams often form braided channels here.

Question 21

What is the Distal zone>

Answer 21

Furthest from ice margin. Drainage pattern meanders on flood plain.

Question 22

What are eskers?

Answer 22

Long, sinuous ridges of sand and gravel deposited by meltwater tunnels. They can become beaded eskers if there are buildups of sediment in areas where the tunnels were blocked for a period.

Question 23

How are eskers formed?

Answer 23

Through subglacial meltwater deposition - when meltwater streams deposit sediment due to the stream being blocked. Another method is when a delta of fluvioglacial material extend outward perpendicular to the ice margin.

Question 24

What is a kame and how is it formed?

Answer 24

A steep-sided conical hill. They are formed by deposition of material in ice in surface depressions or crevasses. These erode their way down through the ice and are deposited at the base as kames. They show evidence of stratification but the bedding can be disturbed by meltwater streams.

Question 25

What is a kame terrace and how is it formed?

Answer 25

Relatively continuous bench-like features along valley side. Formed when a gap between valley side and ice is filled with fluvioglacial deposits.

Question 26

What is an outwash plain?

Answer 26

A gently sloping surface of rounded, sorted and stratified sands and gravels with partial size becoming smaller as the meltwater loses energy. They are formed by a stream rapidly exiting the snout, depositing material. The braided drainage channels can continue to deposit.

Question 27

What are kettle holes?

Answer 27

They form in outwash plains where ice was buried beneath gravels or sands. After the ice melted, the ground fell in to form a depression. These fill with water and undergo succession to become a hydrosere. They can be between 400 and 1500 metres in diameter and form lakes

Question 28

What is a proglacial lake?

Answer 28

Meltwater exiting becomes impounded within a depression blocked by ice and high ground. They are temporary and could empty rapidly during deglaciation.

Question 29

What are strand lines?

Answer 29

They occur when water was stationary for a long time - sediment deposited at the edges of a lake as it was fed by meltwater.

Question 30

What are varves?

Answer 30

Deposits at the bottom of a proglacial lake. There are alternating bands of sand overlain by dark-coloured silt/clay. These bands reflect the amount of annual discharge.

Question 31

What are overflow channels?

Answer 31

Formed when proglacial lakes overflow. They are an open V-shape often gorge-like and sinuous. These are caused by intense fluvial erosion as the overflow erodes a channel out of the like. Many are now dried up after the lake drained away during deglaciation.