Lecture 5 - material transport

Question 1

define exogenetic

Answer 1

a process originating at or near the surface of the earth e.g. denudation; a destructive process

Question 2

define endogenetic

Answer 2

a constructive process; formed / occurring beneath the surface of the earth

Question 3

what 2 things does denudation require?

Answer 3

1 - weathering of rock

2 - removal weathered material

Question 4

key systems:

Answer 4

• the glacial system
• the fine-grained debris system
• the course-grained debris system
• the geochemical system

Question 5

what is transport capacity?

Answer 5

the idea that water should transport as much sediment as the flow capacity allows

Question 6

what is a supply limited river?

Answer 6

the river is carrying all it can detach / access; the amount of lowering is limited by the stream’s ability to detach material from the bed

Question 7

what is a transport limited river?

Answer 7

all capacity is being used to transport; the amount of lowering is limited by the capacity of the stream to transport sediment

Question 8

overview of fluvial channels

Answer 8

• drag increases velocity
• velocity increases with slope and discharge
  complicated by:
• 2 modes of transport: suspended + bed load
• range of sediment size
• transport below capacity unless armour

Question 9

overview of hill slopes

Answer 9

• rates are very dependent on material properties esp. particle size, conditions, and vegetation
• erosion by overland flow

Question 10

overview of debris flow

Answer 10

• occur in colluvial channels
• extreme capacities
• similar to fluvial but extreme sediment concentration means collisional between particles v important
• hyper-concentrated flows have less particle contact

Question 11

overview of gravity slides

Answer 11

• energy dependent on elevation and slope

- failure triggered by steepening of slope or some change in material strength or cohesion

Question 12

overview of glacial

Answer 12

• most complex
• array of transport paths and mechanisms
• transport capacities of superglacial and subglacial huge

Question 13

functional geomorphology

Answer 13

• describes a ‘process framework’ or ‘general model’ of landscape evolution processes
• coupling of processes is hugely important, especially uplift and erosion processes in mountainous regions
• requires a complete understanding of processes and their rates and their spatial and temporal patterns

Question 14

functional realms: high energy and cold =

Answer 14

1. course grained

2. glacial

Question 15

functional realms: low energy and warm =

Answer 15

1. fine grained

2. geochemical

Question 16

general conditions of elevation:

Answer 16

• elevated areas tend to have steep slopes
• elevated materials have greater potential energy and hence gain more kinetic energy when falling
• high topography attracts precipitation
• freeze-thaw processes are most effective

Question 17

general considerations of material strength:

Answer 17

• ability to resist moving downhill depends on shear strength
• bedrock: rock mass strength is important
• sediment: cohesive strength is important

Question 18

general considerations of high energy, cold:

Answer 18

• steep gradients
• freeze thaw
• high precipitation
• strongly seasonal snow and ice melt
• fast incision by supply limited processes

Question 19

general considerations of low energy, warm:

Answer 19

• no freeze thaw
• low gradient
• extreme events rare
• capacity limitations means deposition dominates - system more open
• geochemical weathering important

Question 20

fluxes of material depends on?

Answer 20

• weathering rates
• material properties
• energy available