|The active crater within the caldera of Halemaumau on the|
summit of Kilauea. The rim is about 150 meters across,
and the lava is about 100 m below the rim. USGS.
|Cover image of Krafla from Geology magazine,|
A few days ago, the U.S. Geological Survey reported several (?) events in which a section of rock broke off the wall and fell into the lava lake. One of these "rocks" was about 395 feet long and 16 feet wide. It had been hanging over the pit by about 180 feet and so the USGS was able to forecast the collapse. There is great videos of these events here and here. In this video you are looking into the throat of a crater on the floor of Halemaumau (same view as on the photo on the upper left on this post). The walls of the crater form an arch at the top, and you are looking at a lava lake in the bottom of this crater. The molten lava is in the bottom of the crater, about 100 meters down. It is "red hot magma", but the surface cools by radiation to the sky and conduction to the cooler air, and so it is covered with a black crust. Motion of the magma under the crust causes it to crack and move, a miniature version of "plate tectonics." (The USGS made a movie exploring this analogy back in the 1960's or 1970's.)
Does anyone know if this movie still exists or is available to the public?