August 16, 1996

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.

Growth of Lo`ihi Seamount

Floating hydrophones and sonobuoys recorded the crackling and grinding noises that are often indicative of an ongoing submarine eruption, but the University of Hawaii Pisces V dive team and their USGS, Bishop Museum, and University of Washington collaborators found no red lava or active eruptive vents as they explored the underwater world of Lo`ihi volcano last week. The dive team encountered murky waters full of a fine white "dust" that probably came from new hydrothermal vents, but visibilities of less than 5 feet, at times, precluded visual confirmation of eruption.

Volcanoes deep on the ocean floor, like Lo`ihi, usually erupt non-explosively with gentle outpourings of lava. Over about 200,000 years of recurring eruption and layer upon layer of pillow lava, a submarine shield forms complete with a summit caldera and radiating rift zones.

More violent eruptions commence as the edifice grows upwards and reaches within a few hundred feet of the ocean surface. The confining pressure is low at shallow depths, and explosions of ash-laden steam become common. Lo`ihi is probably 100,000 years away from this explosive stage of volcanism. When the summit of a submarine volcano finally rises above sea level, violent, steam-driven eruptions give way to relatively benign activity of the sort witnessed on Kilauea and Mauna Loa in recent years.

Kilauea Eruption Status

The current eruption of Kilauea volcano continues without significant change in Hawaii Volcano National Park. There were no felt earthquakes on the Island this week.