L12: Mass wasting (movement)

Question 1

What is mass wasting (movement)?

Answer 1

Downslope movement of debris by gravity.

May be slow or rapid, and transitional.

Lead to a range of resulting slope forms.

Question 2

What is the 5-element alpine slope model made up of?

Answer 2

1. Interfluve: Mass wasting
2. Free face: Rockfall; avalanche erosion; gully and chute erosion
3. Talus: Rolling and settling; avalanche and mudflow; erosion and deposition
4. Talus foot: Rock glacier flow; protalus deposition
5. Valley floor: Mass wasting; overland flow

Question 3

1. Interluve

Answer 3

Not present in most intensively glaciated areas.

Found where slow mass wasting and deep weathering is.

Relicts signify weak lateral transfer of debris.

Slopes steepen around the edge of the interluve.

Mass movement gives lobes, terraces and stripes.

Question 4

2. Free face

Answer 4

Very abrupt edge characterises the interfluve

The interfluve is being consumed by the retreat of the free face at 1mm/yr.

Question 5

3. Talus slope

Answer 5

Combination of transport, slowing and storage.

A zone of active weathering.

Rate of development depends on slope foot (actively being removed or building up?)

Without basal removal “alluvial talus” results

Snow increases rate of movement by creating low roughness

Storm evens produce occasional mudflows

Lateral moraine may “interrupt” the talus slope

Serration results if material is very fine (glaciofluvial)

Ice core may be present, and affect future development.

Question 6

4. Talus foot

Answer 6

Highly variable morphology and sediment.

Highly dependent on nature of slope-foot transport and debris removal.

Deep mechanical and chemical weathering continue.

Question 7

5. Valley floor

Answer 7

Deglacial debris often dominates over slope debris

Bedrock outcrops common

Fluvial processes active

Question 8

How are rock glaciers formed?

Answer 8

It can form when ice and snow melt on the surface of a talus slope, infiltrate down through the rocks, and then freeze at depth.

The result is a mass of rocks that are cemented together by ice.

Rock glaciers that form from the wasting of glacial fronts or by accretion at glacial fronts often have this configuration.

Question 9

Rock glaciers in Switzerland

Answer 9

994 active rock glaciers in Swiss Alps
Total amount of talus on move = 500-800 x106 m3
Mass wasting by active rock glaciers / year is 450-600
x 106m x t (horizontal) and 140-190 x 106 m x t
(vertical) for a movement of 0.3 m/yr and a slope of 30
% (17o)
On average, every individual transports a volume of
1.2-1.6 x 10 m of talus and ice, with a speed of 5-100
cm/year (Barsch, 2007)