Lesson 12: Glacial Meltwater

Question 1

What are the 2 main sources of meltwater?

Answer 1

Surface melting and basal melting

Question 2

What is a glacial outburst?

Answer 2

Huge amount of meltwater becomes trapped, either beneath the ice or as surface lakes. When these eventually burst (called a glacial outburst), the surging meltwater has the power to carve deep channels or gorges

Question 3

Where does meltwater travel?

Answer 3

Supraglacial
Englacial
Subglacial

Question 4

Meltwater discharged from where is higher in the summer months?

Answer 4

Supraglacial and subglacial streams

Question 5

Define moulins

Answer 5

Vertical shafts cut out by the water, where water cascades down these into the ice sheet. Remain open by constant melting by water

Question 6

How do fluvio-glacial deposits differ from glacial deposits?

Answer 6

1) Generally smaller due to the lesser energy of the meltwater streams in comparison to valley glaciers
2) Generally smoother and rounder through water contact and attrition, as well as being sorted and graded
3) Sorted horizontally, with the largest material found up-valley (nearest snout)
4) Stratified vertically with distinctive layers which reflect either seasonal or annual sediment accumulation. During summer months when discharge is high, heavier material is found further down and deposited

Question 7

Define imbrication

Answer 7

Shows the direction of flow (specifically the sorting horizontally and vertically)

Question 8

Describe proximal zone of outwash plains

Answer 8

Immediately in front of the glacier, close to the snout. Meltwater has the greatest power here so particle size may be large

Question 9

Describe medial zone of outwash plains

Answer 9

Further from the ice margin- meltwater streams tend to anastomose and form braided channels because of high daily and seasonal variation. Particle size is more rounded due to attrition

Question 10

Describe distal zone of outwash plains

Answer 10

Furthest from ice margin- broad flood plain- well sorted sediment and even smaller and rounded than medial zone

Question 11

What are the 2 types of fluvio-glacial landforms?

Answer 11

Ice contact
Pro-glacial

Question 12

Describe kame

Answer 12

Undulating mound of fluvio-glacial sand and gravel deposited on the valley floor near the glacial snout

Question 13

Process of formation of kame

Answer 13

Meltwater streams emerge onto the outwash plain or proglacial lake at the glacier snout, their velocity falls and sediment is deposited

Question 14

Example of a kame

Answer 14

Yellowstone NP, Wyoming

Question 15

Describe kame terrace

Answer 15

Flat, linear deposit of sand and gravel deposited along the valley sides

Question 16

Process of formation kame terrace

Answer 16

Valley sides radiate heat in the summer, melting the edges of the glacier, forming meltwater streams which deposit sediment. When the glacier retreats the sediment falls to the valley floor, forming a kame terrace

Question 17

Example of kame terrace

Answer 17

Chilliwack river valley, Canada

Question 18

Describe esker

Answer 18

Long, narrow, sinuous ridge of fluvio-glacial sand and gravel

Question 19

Process of formation esker

Answer 19

Subglacial streams carry large amounts of rock debris due to high hydrostatic pressure inside tunnels. Streams often meander beneath glacier. Glacial retreat cause debris to be deposited

Question 20

Example of esker

Answer 20

Mount Pelly, Nunavut, Canada

Question 21

Describe sandur (outwash plain)

Answer 21

Flat expense of fluvio-glacial debris in front of glacial snout

Question 22

Process of formation of sandur

Answer 22

Meltwater streams emerge from glacier and enter lowland areas, they lose energy and deposit debris loads. Coarse gravel deposited first near glacier, then sands, then clay

Question 23

Example of sandur

Answer 23

In front of Red Glacier, Alaska

Question 24

Describe kettle hole

Answer 24

Circular depression often forming a lake in an outwash plain

Question 25

Process of formation kettle hole

Answer 25

Glacier retreats, detached blocks of ice remain on the outwash plain. Meltwater streams flow over the ice covering them in deposits. Ice melts a debris subsides to form a depression which can fill with meltwater

Question 26

Example of kettle holes

Answer 26

Yama Peninsular, Siberia

Question 27

Describe proglacial lake

Answer 27

Lake formed in front of glacial snout

Question 28

Process of formation of proglacial lake

Answer 28

Damming action of a terminal or recessional moraine during retreat of a melting glacier. Or meltwater trapped against an ice sheet from isostatic depression of the crust around the ice

Question 29

Example of proglacial lake

Answer 29

Lake Michigan - part of an old proglacial lake

Question 30

Describe meltwater channel

Answer 30

Narrow cut channel into bedrock or deposits, either underneath or along the front of an ice margin

Question 31

Process of formation of meltwater channel

Answer 31

Meltwater can erode deep channels from high hydrostatic pressure within glaciers, and high sediment load. Able to flow uphill and are larger than post-glacial streams. Braiding is common

Question 32

Example of meltwater channel

Answer 32

Pentland Hills, Cairngorms, Scotland