Kilauea's shrinking crater

I was walking to the Jaggar overlook one day and happened upon a ranger. I asked her about the history of the crater and why it was so small. She explained that over time, the crater has receded. She pointed out landscape feature to me as evidence. If you look at the landscape, you can see the outline of larger craters that contain smaller craters. The pictures below illustrate this. In all, we counted 4 of them (we were just guessing based on the terrain.)