I know giant meteorite impacts are much cooler, but...
How do we know it isn't a volcanic depression?
There's a supervolcano burbling away underneath Yellowstone National
Park, just waiting to erupt again in a display that will make Mount St.
Helens look like a mildly rainy day. And I recall the caldera, which
looks like a huge depression in the ground, is about 20 miles across.
Mount Olympus on Mars has a caldera over 40 miles across.
Either way, nature is at least awfully exciting while it is being
frighteningly destructive, be it volcano or giant killer space rock.