For centuries, sky watchers have reported seeing mysterious flashes of light on the surface of the Moon. Modern astronomers have observed the same phenomenon, but no one has been able to satisfactorily explain how or why the Moon sporadically sparks. However, researches now believe they have found the cause.
Researchers have examined the chemical content of Moon rocks retrieved by 9 astronauts during the Apollo missions and have found that they contain volatile gases such as helium, hydrogen, and argon. The researchers suggest that stray electrons, freed when the rock cracks, may ignite these gases. Indeed, lunar rock samples, when fractured in the lab, throw off sparks.
What causes these rocks to crack on the lunar surface? The flashes are most often seen at the borders between sunlight and shade on the Moon, where the surface is being either intensely heated or cooled. A sudden change in temperature may cause thermal cracking. Another possibility is that meteors may strike the rocks and cause them to crack. Finally, lunar rocks maybe fractured by seismic events-in the other words, by tiny moonquakes.
Reference: absoluteastronomy.com
All of the following are given as reasons for Moon rocks cracking EXCEPT
seismic actions
sudden temperature changes
the action of meteors
the pressure of gases