Our Beautiful World
When pahoehoe lava enters the ocean for extended periods of time, new land is created in the form of a fan-shaped platform known as a lava delta. Lava pouring into the ocean from either surface flows or lava tubes cools rapidly, usually shattering into sand- to block-size fragments. These fragments accumulate along the submarine slope to form a loose foundation that will eventually support overlying flows that build the delta above sea level.
When the lava fragments accumulate on a relatively steep submarine slope, the leading edge of a lava delta will collapse frequently to form a series of submarine landslides. These collapses can sweep unwary visitors into the sea and trigger strong explosions. A lava delta will grow both laterally and seaward until a collapse occurs or the supply of lava to the ocean is interrupted.Typical growth of a lava delta at Kilauea Volcano
1) Pahoehoe lava first enters ocean quietly
2) Lava fragments tumble down a submarine slope
These loose lava fragments form the unstable foundation for all subsequent lava flows and loose debris. The volcanic debris along the submarine slope consists chiefly of angular pieces of glassy lava produced by rapid cooling and blocks of large cylindrical lava tongues and pillows from stubby submarine lava flows. Also, during a recent series of deep-water scuba dives, scientists observed a small channeled lava flows as wide as 1.5 m moving down the leading slope of the submarine delta; highly fractured, these intact flows apparently interfinger with the loose fragments.
3. Lava flows build lava delta across loose debris
As the loose debris builds a foundation forward and upward, small
lava flows spread atop the debris to form a lava delta above sea
level that may extend tens to hundreds of meters beyond the old
shoreline. At the same time, the entire delta can slowly sink as
the submarine debris pile shifts under the weight of the overlying
lava flows; recent studies of several growing lava deltas showed
that they subsided several centimeters per month. This new land
is ***extreme***ly unstable!
4) Lava tube system develops in delta
As the lava-flow field on the delta matures, a lava tube system
usually develops and laa may enter the ocean from one or more tubes.
The exit points of these lava tubes often reside at, or below, sea
level and are usually marked by a single, vigorous steam plume.