August 9, 1996

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

Submersible Studies of Lo`ihi Seamount

In response to the intense off-shore earthquake swarm that began on July 16, scientists at the University of Hawaii (UH) received funding for a research cruise to investigate possible changes at Lo`ihi. On Friday, August 9, the University of Hawaii research ship Kaimikai o Kanaloa launched the manned submersible vessel Pisces V for its second reconnaissance dive to the underwater volcano.

Fortunately, during the past week, earthquake activity near Lo`ihi has diminished, and it appears as though this episode is coming to an end. The Hawaiian Volcano Observatory seismographic network recorded a total of 4,377 Loihi earthquakes from July 16 through August 8.

As we have reported elsewhere, nearly 100 of these earthquakes were of magnitude 4 or greater. One of the larger earthquakes on Tuesday, August 6, was felt through the hull of the Kaimikai o Kanaloa, and, if large earthquakes had continued, the shipboard scientists would not have been able to dive with the Pisces.

The large number of earthquakes and the numerous larger earthquakes suggest that Lo`ihi may have undergone significant changes. The first of the UH scientists to dive with the Pisces on Thursday reported seeing a new pit crater, indicating that a collapse of the Lo`ihi summit region had occurred. This collapse occurs when magma is drawn from beneath the summit region of the volcano, leaving no support for the overlying rock mass.

The second dive is aimed at exploring other parts of Lo`ihi, looking for more evidence to determine possible causes of the earthquake swarm and to document other changes visible around the volcano. This research cruise is expected to generate a great deal of data that scientists will study to learn about the processes associated with the growth of a young Hawaiian volcano.

Kilauea Eruption/Earthquake Update

While the Lo`ihi activity has been the recent focus of much of our attention, regional earthquake activity beneath the island of Hawai`i also continues. Two earthquakes were felt from beneath the Kilauea south flank, about 25 miles south of Hilo on the night of August 8. The first of these earthquakes occurred at 10:25 p.m. and the second occurred at 10:36 p.m. Their magnitudes were 3.9 and 3.4, respectively. Small earthquakes like these continue to remind us of the ongoing geologic processes shaping the island, and of the ever-present need to be aware of the geologic hazards, such as volcanic eruptions, large earthquakes and tsunami that may be generated with large earthquakes.

The Kilauea eruption continues unabated, and flows enter the ocean only in the Lae`apuki region. The lava pond within Pu`u `O`o was sluggish during the past week, and the level was about 325 feet below the lowest part of the rim. A glow from the pond reflecting off the fume cloud over the cone often can be seen at night.

Television crews from programs on the Turner Broadcasting System (TBS), British Broadcasting Company (BBC), The Discovery Channel (TDC), and the Arts & Entertainment (A&E) channel were filming operations of the U.S. Geological Survey's Hawaiian Volcano Observatory during the past week. HVO personnel were busy demonstrating various volcano monitoring techniques and providing interviews for the video productions.

The two south flank earthquakes mentioned above are the only ones reported felt during the past week.

If you feel an earthquake, we would be interested in receiving that information. Please call HVO at 967-7328 and tell us when and where you felt the Earth move.