6.2 They may be lowering of the floor after an eruption : formation of caldera
Before an eruption, the magma chamber size increase and decrease a lot during an eruption creating a big hole inside the Earth. The material on the top, lots of time it is the top of the volcano, are not stable an fall. This event creates a crater after the formation of the ring fault.
“A caldera is a large, usually circular volcanic depression formed when magma is withdrawn or erupted from a shallow underground magma reservoir. It is often difficult to visualize how calderas form. This simple experiment using flour, a balloon, tubing, and a bicycle pump, provides a helpful visualization for caldera formation.”