Gravity well

There were naturally occurring gravity wells on Archetryx. (PROSE: The Apocalypse Element)

On Mars, a decaying segment of the Key to Time was disguised as the capstone of a pyramid. When Zara converted it to its true form, a gravity well was created that caused earthquakes and hurricanes for three decades. This devastated the civilisation of the Ice Warriors. (AUDIO: The Judgement of Isskar)

The pages of River Song's diary were soaked in the gravity wells at the end of time. (AUDIO: Friend of the Family)