Four Basic Geological Processes
• Impact cratering
– Impacts by asteroids or
comets
• Volcanism
– Eruption of molten rock
onto surface
• Tectonics
– Disruption of a planet’s
surface by internal stresses
• Erosion
– Surface changes made by
wind, water, or ice
Impact Cratering
High kinetic energy of
impacting object
 Excavation
 Heat
Shape round for all impact
directions
Crater Morphology:
• Impactor in the inner
solar system can
have 10s of km/sec
relative velocity
• May vaporize or
liquefy a significant
amount of the target
for a large impactor
• “Simple” craters are
bowl shaped
• “Complex” craters
are flatter, and have
a central uplift or
peak
Impact
Craters
Tycho (Moon)
Meteor Crater (Arizona)
The Impact Process
1. Detonation - shockwave propagates through
target, projectile vaporized
2. Excavation - target is heated, vaporized,
liquified, solid material is ejected (possibly above
escape velocity!)
3. Rebound - in larger craters, the target may
“bounce back” viscously, forming a central uplift
4. Relaxation - crater walls subside, melt pools in
the crater
Few Hundred Confirmed Craters on Earth
Meteor Crater
Manicouigan Crater
Moon Near Side
Moon Far Side
Lunar Highlands
Mare Imbrium
Lunar Mare
Crater modification
Mars Rampart Crater 3
Venus Craters 1
Ganymede Crater Chain
Shoemaker-Levy 9
SL-9 Aftermath
Hyperion