September 27, 1996

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

More Submersible Work on Loihi

Scientists from the University of Hawai`i at Manoa are once again engaged in a research cruise over Lo`ihi, the submarine volcano southeast of the Island of Hawai`i. This research cruise, and another research cruise next week, were scheduled much earlier. However, with the intense earthquake swarm that began in mid-July, and with the findings of the specially arranged cruise in response to the July earthquake swarm, the focus of the September and October cruises has changed somewhat.

The Hawaiian Volcano Observatory seismographic network continues to register earthquakes originating from Lo`ihi. In recent weeks, the rate of earthquake activity has decreased: from the 1052 Lo`ihi earthquakes located in July, to 142 in August and 29, to this date, in September. This decrease in activity has allowed the scientists to use the manned submersible vessel Pisces V for their reconnaissance work.

The scientists have been looking for evidence that will suggest probable causes of the July-August earthquake swarm. They are looking for indications of recent eruptive activity and for new volcanic vents. They are also exploring the new features visible at the summit of Lo`ihi, where a crater dubbed Pele's Pit was formed. It is quite likely that Pele's Pit formed in connection with the earthquake swarm.

Besides trying to determine the causes of the earthquake swarm, a very important element of this research cruise is to develop a new map of the ocean bottom at Lo`ihi. With sophisticated sonar mapping tools onboard the Pisces V mother ship Ka`imikai o Kanaloa, detailed bathymetric maps can be drawn. Like a topographic map of the island, the bathymetric maps will show the pit craters and other features that scientists will have to incorporate into their interpretations of the Lo`ihi data.

The bathymetric maps will also help the Hawai`i Undersea Geo Observatory, or HUGO, project. This project is being spearheaded by UH-Manoa scientists and will involve HVO in the data acquisition, analysis, and transmission. Prior to the July earthquake swarm, the HUGO plan was to place their base station near the place where Pele's Pit formed. Needless to say, that plan has changed, and the newly acquired bathymetry will help the HUGO team determine a new location for their equipment and allow the project to move ahead.

Eruption Update

The eruption from flank vents on the western side of Pu`u `O`o continues unabated, with lava flowing through the six-mile long tube system and entering the ocean at Lae`apuki. During the past week, the HVO seismographic network recorded and located 140 earthquakes. None of these earthquakes were reported as felt by anyone on the island.