We went to Hawaii and visited the Volcanoes National Park. People were walking inside a volcano crater. They said that not long ago hot lava was swirling around inside of the crater. In some spots steam was coming up through the vents. Just how thick is the hardened lava there before you can walk on it? And is there molten lava still underneath there? YIKES!

rocky

I think the crater you are thinking of is Kilauea Iki. The crater has been there for a long time (it formed by collapse probably before even the Hawaiians arrived). There was a spectacular eruption from a vent on the wall of the crater in 1959. There were very high lava fountains (up to 580 meters high) and lots of lava flowed into the crater. Before this eruption the crater was about 200 meters deep, and after the eruption ended it had been filled to the point that it was only 87 meters deep.

I don't know when the first people walked out onto the solidifying crust, but the first study of the rate at which the lava was cooling was published in 1966. The scientists set up a drill on the crust and drilled down until they met molten lava. They were able to easily determine the thickness of the crust, and by coming back a number of times figure out how fast the crust was forming. It turns out that the fact that the Kilauea Iki area receives a lot of rain is significant in increasing the rate of cooling.

The most recent drilling that I have heard about took place in 1988 and determined that there is still some mushy lava down there, in fact it is about 20 meters BELOW the level of the crater floor prior to the 1959 eruption! How could that be? Perhaps it has melted its way down? Perhaps the weight of all the lava caused the floor to sag down? Maybe some day you'll come to Hawai'i and solve the mystery.

Sincerely,

Scott Rowland, University of Hawaii 

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