The Objects > General Questions

Boulders sitting on edge of craters

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jcordes:
While exploring on Moon Zoo (aka the best site ever) I pondered upon a question concerning boulders.  In my exploration I found many pictures where boulders were concentrated on outer ring of craters.  So I asked myself why have the boulders not rolled into the depths of the craters they find themselves by.  Unfortuanately I have not saved any of the pictures I found.  Please help me gain a farther knowledge about this topic in order to increase my vast inquiry of the moon.

Geoff:
Hi jcordes and welcome to Moon Zoo.

Some boulders will land on the crater rim during the impact process but many more will be ejected around the crater. The boulders on the crater rim will eventually roll/slide down the side of the crater if there is a moonquake nearby or if the boulder fractures due to temperature changes.

This posting: What causes erosion on the Moon may help.

jcordes:
Thankyou Geoff for your contribution to my exploration of the moon.  I am deeply grateful for your help furthing my knowledge about the moon.  In your response you stated that the boulders were ejected from the boulders, what causes the craters to eject from the crater and why do they land, what seems to be uniformly around the circumference of the crater.  Also will these boulders ever find their way to the bottom of the boulder permantely, or will they continue to be ejected.  On the topic of boulder movement, I wonder what causes them to move.  Are there pestilential solar winds from the sun blowing fiercly across the moon pushing the boulders to new positions.  Another response would help me gravely in my continued journey to further my knowledge of the moon.

kodemunkey:
Boulders are ejected from craters during the impact that forms them and is usually a one time thing. As for how and why they move, there are at least two reasons i can remember, a moonquake might shake them from their resting place and send them rolling down a slope. The other way is if they're on a flat surface is the sun heats up the rock during the lunar 'day' which is two weeks long, and they then cool down during the lunar 'night" Over very long periods of time , this is what causes the boulders to move.

Hope that helps  :)

jules:
And just to add to what kodemunkey says - boulders can be flung long distances from their impact site on the Moon so you can end up with boulders in positions hundreds of km away from their originating impact. Tycho is a good example - you can see with the naked eye just how far its rays and, therefore, debris extend.

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