how long does it take for lava to cool once it has reached the surface
Adam, Isaac, and John
Dear Adam, Isaac, and John,
The length of time it takes lava to cool depends on how thick the lava is.
A thin pahoehoe toe of lava will grow a skin on it almost instantly.
This skin is flexible at first but as it thickens it gets harder and
harder. The skin is a very good insulator so this means that the inside
of the toe will cool slowly. A pahoehoe toe that is perhaps 20 cm tall
and 30 cm wide will be able to support your weight within ~15 minutes
after it stops flowing (it will still be much too hot to touch). Some
thick lava flows, those that are a few meters thick, will take weeks
before they are completely solid. The most extreme case is where lava
flows into a pre-existing depression such as a crater or river valley.
These flows can be 10's to 100's of meters thick. The 1959 Kilauea Iki
eruption took place in a pre-existing 200 meter-deep crater and filled it
up a little more than half-way. Although people have been able to walk
across the cooled lava surface since a few months after the eruption, the
most recent drill hole through the surface (in 1988) encountered some
still-mushy lava down at the bottom.
Scott Rowland, University of Hawaii
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