Week 5: Other surface processes

Question 1

Define the term “Saltation”

Answer 1

A process where loose materials are removed from the surface and carried by fluids, before returning to the surface

Question 2

Describe how saltation leads to dunes and dust storms. Give examples for each of these

Answer 2

Dunes:
- Sand subjected to saltation are more likely to stick to sand, but are more likely to bounce when hitting more coherent surfaces. This feedback loop allows sand to accumulate into dunes

• Ex.
• Titan has longitudinal dunes near its equator
• Pluto has dunes made out of methane ice. Methane ice grains are lifted by the melting of surrounding nitrogen ice or blown down from mountains.
• Comets also have dunes, due to particle motion being driven by gas pressure from thermal flow.

Dust storms:
- Saltating grains release more grains as they hit the ground, resulting in a cascading chain of saltation. This results in dust storms as small grains become suspended.

• Ex. Titan has dust storms of organic molecules

Question 3

Describe the term “Sublimation” and give two example of this process.

Answer 3

An exogenic process where atmospheric pressure is low enough to allow heated solid to directly transition to gas phase.

Examples:
1) Mars: When dry ice at Mars’ southern polar caps is heated by sunlight, it sublimates into CO2

2) Pluto: Pluto has an N2-dominated surface containing small pits, which implies the sublimation of nitrogen or CH4 ice

Question 4

Define the term “fault” in tectonic processes and illustrate 2 types of faults.

Answer 4

A planar fracture in a volume of rock, as a result of rock-mass movements which causes significant displacement across the rock

Question 5

Describe the impact process

Answer 5

• As an impactor strike, a shockwave spreads out from the impact site
• This fractures the rock and excavates a large cavity, spreading ejecta in all directions
• Impactor shatters into small pieces, which melts/ vaporize along with some local rocks
• If the impactor is large enough, materials pushed towards the outer edge will slump back to the center and the rock beneath the center will rebound, forming a central peak
• Terraces are formed as crater edges slump

Question 6

Give examples of fluvial processes on Mars and Titan

Answer 6

Mars:
1 - Dendritic Valley networks
2 - Outflow channels
3 - Subsurface volatiles
4 - Recurrent slope Lineae

Titan:
1 - Methane and Ethane lake