Our Beautiful World
The rare explosive eruptions in Hawai'i generally are caused
by the interaction of magma and ground water. The magnitude of
the resulting steam explosion varies from harmless to catastrophic.
Small steam-blast explosions occurred during the 1960 Kapoho eruption
when the magma beneath the vents, which were near sea level, encountered
saltwater trapped in the surrounding rocks. These steam blasts
ejected black clouds of pulverised rock fragments but
A much larger steam-blast eruption occurred at the summit of
Kilauea in 1924, when ground water apparently flowed into the
heater rocks beneath the Halemaumau vent, which had been erupting
nearly continuously for over a century. The explosions continued
at intervals for 2 weeks, carpeting the area around Halemaumau
crater with large rocks and a thin layer of ash. Boulders weighing
several tons were thrown as far as 3,000 feet from the crater.
The greatest hazard
The largest explosive eruption on Hawai'i within historical time
occurred in 1790. This eruption produced pyroclastic surges that
originated at Kilauea's summit and flowed several miles to the
Southwest. Pyroclastic surges are ***extreme***ly dangerous because
they move at speeds of 30 to
The thick deposits of ash exposed at many sites on the island
indicate that even larger explosive eruptions occurred in prehistoric
times and probably originated from Mauna Kea as well as from Kilauea.
Explosive eruptions of any size take place infrequently in Hawai'i,
but the possibility of one occurring in our lifetime should not
be totally discounted. Such eruptions are unlikely to begin without
some warning. The most widespread hazard from an explosive eruption
would be windborne ash, which could damage structures, machinery
and agricultural crops.