[gleeaikin]

My guess is that the shiny flowing looking streaks are molten glass which slopped over the sides.

[The Cajun]

Not saying it was caused by flowing, but really looks like you said, that some highly reflective material *slopped over the sides*.
Especially on the right side where there appears to be some curvature to the ?flow?

[SunkenCiv]

The moon is so small and irregularly shaped, the horizon varies a great deal but would appear to be just over the next rise to a visitor to the surface. Those lines are from rolling debris after the impact.