EAE3311 Lecture 6 Flashcards

1
Q

Describe weathering through:

Frost cracking

2 points.

A
  • Frost cracking occurs in a narrow temperature range of -3℃ to -10
  • Water penetrates rocks and when this water freezes the liquid water migrates to the freezing front and freeze in existing spaces like existing cracks and expands them.

EAE3311 4aa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Describe weathering through:

Salt and Plants

2 points.

A
  • Salt cracking is a type of cracking is seen in arid environments, where crystals grow in existing cracks and expand them (like frost).
  • Plant roots also grow in cracks and can widen them.

EAE3311 4ab

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Describe weathering through:

Tectonics

2 points.

A
  • Rocks can crack below the surface (deep in the crust) ‘rock crusher tectonics’.
  • Rocks arrive at the surface pre-cracked.

EAE3311 4ac

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is regolith?

A

Rocks arriving at the surface of the Earth arrive in a reactive zone and start becoming regolith (weathered rock) through a variety of process.

EAE3311 4ad

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the layers of regolith?

3 points.

A

Regolith is divided into three layers

  • Weathered Rock: Fractures appear and some chemical weathering starts
  • Saprolite: Retains the original rocks structure but is fragmented enough to dig through
  • Mobile Regolith: Detached from the layers below it. In motion vertically and laterally

EAE3311 4ae

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the processes of erosion?

3 points.

A
  1. Weathering: disintegration of rocks on the surface
  2. Transport: material transported (by rivers) to the ocean
  3. Corrasion: material in the river further corrades the channel creating more material.

EAE3311 4af

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is transport-limited erosion?

A

The fact that the bedrock is blanketed by mobile material indicates transport-limited erosion: what is determining is not the weathering of the bedrock, it is the transport process.

EAE3311 4ag

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is weathering limited erosion?

A

In weathering limited erosion, erosion is limited by the rate the rock debris is loosened from the bedrock. In these areas, a blanket of regolith (e.g. soil) will not form

EAE3311 4ah

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Mobile regolith has a net downslope motion through what processes?

3 points.

A
  • Gravity
  • Biology
  • Weather (meteorology)

EAE3311 4ai

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is Rainsplash?

A

Direct impact of raindrops blasts grains from the soil surface. On a slopped surface, the ejected grains travel longer downhill than uphill resulting in a net flux of material downslope which is proportional to the slope

Where vegetation covers the surface, rainsplash and sheet wash are ineffective in moving particles from place to place

NB: Kinetic energy of the drop ∝ # and velocity of grains

EAE3311 4aj

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How is soil creep measured?

4 points.

A

Use of cosmogenic nucleotides like ¹⁰Be

  • The creep of regolith down a hill slope is generally very slow (rates like 2 mm per year).
  • Can’t be measured in real time
  • ¹⁰Be found in the atmosphere. Attaches to clay particles.
  • The longer the exposure of the clay particles to air the more ¹⁰Be on the them.

Note: Soil creep is a very slow, but deterministic process, can be modelled (we can imagine what this hill will look like over time)

EAE3311 4ak

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are Stochastic events?

3 points.

A
  • Occur alongside deterministic processes
  • e.g. Landslides
  • A threshold process: a FAILURE

Interesting but difficult to predict. Faster event

EAE3311 4al

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why do hillslopes fail?

4 points.

A
  1. Tectonic tilting
  2. Toe cut out by the river
  3. Cohesion forces have changed
  4. Water saturation

EAE3311 4am

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is internal friction?

A

The friction angle (angle of internal friction)

Property of material

  • Dry sand 𝚽 = 31 degrees
  • Most regolith = 20-40 degrees

EAE3311 4an

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the ‘critical zone’?

3 points.

A

Top of vegetation to the bottom of the groundwater

Most landscapes on Earth are blanketed by a mobile layer of material derived from bedrock through the process of weathering. This blanket is called the ‘critical zone’ (top of vegetation to the bottom of the groundwater)

  • Hillslopes cover the majority of Earth’s surface
  • Can be soil mantled (rounded and smooth) or bare (steeper and jagged)
  • Lead to channels

EAE3311 4ao

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the types of rock weathering?

4 points.

A
  • Tectonics
  • Salt and Plants
  • Frost cracking
  • Thermal stress and strain

EAE3311 4ap

17
Q

Describe weathering through:

Thermal stress and strain

3 points.

A
  • Rocks expand when heated. if this is uneven strain forms and if this exceeds the strength of the material it fails. For example.
  • Fires can spall (onion weathering) large proportions of the rocks in the fire zone to a depth of centimeters).
  • Day/Night cycles probably result in microfractures. Cracks in boulders tend to have a N/S orientation.

EAE3311 4aq

18
Q

What impacts internal friction?

A

Affected by three elements of reality:

  • Water
  • Cohesion by minerals
  • Cohesion by roots

Plants improve cohesion both by cohesion and by removing water (transpiration)

Cohesion can generate slopes that exceed the internal friction of the system