Download Needed for Lab 2 Goals of Today’s Lecture Lab 2 • Protractor

Lecture 3: Intro to Geomorphology

Needed for Lab 2 Lab 2 • Protractor • Transparent ruler • Orange or red colored pencil

Goals of Today’s Lecture 1. Discuss mass continuity as applied to the landscape. 2. Establish the mechanisms that drive U (uplift rate) 3. Examine the linkages between the uplift of mountains, the development of topographic relief, and climate 4. Examine a class of landforms that are controlled primarily by local structural geology and igneous activities.

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Lecture 3: Intro to Geomorphology

Mass Continuity The law of conservation of mass states that the mass of a closed system will remain constant, regardless of the processes acting inside the system. An equivalent statement is that matter changes form, but cannot be created or destroyed.

I – O = ΔS

Application to the landscape:

I = Input of sediment O = output of sediment ΔS = change in storage

Mass Continuity

Input

z

Output

If I = O then ΔS = zero So z is constant

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Lecture 3: Intro to Geomorphology

Mass Continuity

Input

z

Output

If I > O then ΔS increases So z must increase

Mass Continuity

Output

Input

z

If I < O then ΔS decreases So z must decrease

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Lecture 3: Intro to Geomorphology

Two types of landscapes Bill Dietrich

Bedrock landscape

Soil mantled landscape

Bill Dietrich

Conservation of mass for a soil covered landscape Consider the following situation

Elevation (z)

Landscape surface Soil thickness (h)

soil/sediment Bedrock surface bedrock

dz dt

=0

Which means the change in elevation over some time period

∆z ∆t

=0

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Lecture 3: Intro to Geomorphology

What happens if we introduce weathering processes?

Elevation (z)

Landscape surface Soil thickness (h)

soil/sediment Bedrock surface

Rock converted to sediment bedrock

dh Weathering produces soil, thickening the profile.

P=

Converted Rock

dz

dt

dt

=

dh dt

-P

What happens if we uplift the landscape from below? Soil thickness (h)

Elevation (z)

dz

Landscape surface soil/sediment Bedrock surface

Rock converted to sediment bedrock

dh UPLIFT If the landscape also undergoes regional uplift:

U=

Uplift

dz

dt

dt

=U+

dh dt

-P

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Lecture 3: Intro to Geomorphology

What happens if we introduce deposition at the surface?

Elevation (z)

dz

Landscape surface Soil thickness (h)

soil/sediment Bedrock surface

Rock converted to sediment bedrock

dh UPLIFT If there is deposition of material on the surface, by whatever process, dz and dh will increase further.

dz dt

=U+

dh dt

-P

Remember this one!

Conservation of mass for a soil covered landscape dz dt

=U+

dh dt

-P

In order to make meaningful predictions of landscape evolution with this equation, we need to use physical laws to replace the soil thickness term (dh/dt). We do this by writing the following expression:

dt

=P-

·∆

dh

qs

Remember this one!

The change in soil thickness with time is equal to the rate at which rock is converted to soil minus the change in sediment flux over a landscape element or the sediment flux divergence.

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Lecture 3: Intro to Geomorphology

Divergence of Sediment Transport Rate dqs

=0

dx

z x

z x

Divergence of Sediment Transport Rate dqs

>0

dx

z x

Must erode z x

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Lecture 3: Intro to Geomorphology

Divergence of Sediment Transport Rate dqs