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Partial collapse of lava delta triggers littoral lava fountains
and bubble bursts.

A partial collapse of a delta's leading edge may significantly fracture the solidified rock
around the active lava tubes, which allows seawater to seep into the tube system.
When seawater and lava mix within the confines of a lava tube, pressure may build to cause explosions that blast a hole through the roof of the tube. Two types of steam-driven explosions may be generated in such a 'confined' environment; littoral lava fountains and bubble bursts.

Littoral lava fountains

Aerial view of littora lava fountain on an active lava bench.

Cross-section of a littoral lava fountain and lava tube beneath.

Spectacular and rare, this type of lava-seawater explosion produces fountains of molten
lava and steam that reach heights of more than 100 m. The explosions of molten spatter,
bombs, and smaller tephra fragments quickly build a circular cone on the subsided lava delta, sometimes in a matter of minutes. Originating from deeper within the subsided delta and closer
to the shoreline than bubble bursts, littoral lava fountains are much more energetic
and dangerous.

Bubble bursts

Bubble bursts are characterised by sporadic bursts of molten, dome-shaped lava sheets
emanating from a circular rupture in the roof of a tube a few meters inland from the shoreline. Individual bubbles can reach diameters of 10 m in less than 2 seconds before they burst.
The bubble fragments continue on their radial trajectories for up to 10 m before falling to the ground. At the end of a burst, a pool of lava that remains in the roof of the lava tube gradually drains away. These bursts are frequently accompanied by a loud 'boom' that shakes
the entire delta.


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