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Earth Surface Processes > Geomophology - 5 > Flashcards

Geomophology - 5 Flashcards

1
Q

Inferential methods of modelling

A

Digital elevation model analysis

Satellite analysis

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2
Q

What is measured in fluvial monitoring and modelling

A

Analysis of river incision rate scales with stream power
Discharge

Sediment yells studies

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3
Q

Experimental methods

A

1) stimulation of corrosion in lab
2) absolute cosmogenic dating
3) absolute thermochronometry

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4
Q

Stimulation of corrosion in the lab

A

Abrasion in a stimulated fluvial transport shows a supply limited state is most effective

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5
Q

How are cosmogenic isotopes formed

A

In bedrocks by the interaction of cosmic data with the nuclei of atoms

Production decreases with depth

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6
Q

Why is cosmogenic dating used

Terrestrial cosmogenic nuclide concentrations

A

Obtain exposure age ( assume zero erosion since the exposure event)

Obtain an erosion rate (assuming that erosion has been steady)

Obtain catchment wide average erosion rates in fluvial sediments, mean catchments

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7
Q

Example of an ideal exposure event

A

Glacial erosion

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8
Q

What landform can be measured through TCNC dating

A

Faults as they become exposed to cosmic rays

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9
Q

What do concentrations of TCNC rays show

A

Concentration increase with time then saturated

Erosion decreased the concentration predictably

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10
Q

Darvill

A

2013

Exposure and nuclide concentration rates graph

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11
Q

Example target minerals in cosmogenic dating

A

Olivine
Quartz
Pyroxene

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12
Q

What does absolute - thermochronometry determine?

A

The age of closure by measuring volumes of U, Th and He in individual grains

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13
Q

How can he be measured ?

A

By the decay on uranium and thorium in mineral grains

He is trapped and retained at 40-70 oC

+70oC He diffuses our of the grain entirely

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14
Q

What are isotherms used for

A

Following the surface topography allowing dating of valley ages

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15
Q

What does a bent isotherm mean

A

Absolute He ages can date topography

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16
Q

Samples near the valley centre of A HE are ..

A

Older

As they cool earlier and age reflects the pattern of rock uplift

Age pattern is a mirror image of elevation

17
Q

What is modelling

A

Provides a crucial means of scaling up observations

18
Q

Problems of models

A

Stimulation only as good as the process formulations put in

Can’t observe the interactions over while mountain ranges and Ma
-time and scales

19
Q

What is stream power erosion model concept

A

Measures Fluvial incision through an empirical stream power erosion model

20
Q

Egholmet

A

2013

21
Q

Egholmet 2013

A

Couples stream power and hill slope diffusion model

Alpine fault model shows uplift and erosion patterns

22
Q

2013

A

Darvill

23
Q

Darvill 2013

A

Cosmogenic nuclide analysis used on a wide range of land forms from hundreds to millions of year’s

Commonly used isotopes - Al,Cl, C

Uncertainties in dates reduced by improving number and quality of global distribution of calibration sites - aided by CRONUS Earth

24
Q

House

A

1998

25
Q

1998

A

House

26
Q

House 1998

A

Sierra Nevada dating U-Th/He ages

Mapping at river incision, mainly using phosphate minerals (apatite)

Concluded Sierra Nevada developed Andean scale topography between 185my and 80my coinciding with crustal thickening

27
Q

Willet

A

1999

28
Q

1999

A

Willet

29
Q

Willet 1999

A

Numerical model of couples process, tectonic deformation and surface erosion developed to investigate their interaction

Give erosion a number, number determines time required for a system to reach steady state and final topographic shape and size of belt

S alps of New Zealand, thermochronometric measurements and metamorphism indicates 11mm/yr of convergence

Earth Surface Processes (9 decks)

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