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Rockfall in Halema'uma'u
Full details at: http://gallery.usgs.gov/videos/416
The level of the lava lake sometimes changes abruptly. These cycles of rise and fall, which amount to a vertical change of around 15 m (about 50 ft), are occasionally triggered by rockfalls. Here, a small collapse from the vent wall triggers degassing and a drop in the lava level.
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