Recent Activity at Loihi Volcano

Events during 17 July to 31 July 1996 :

The precursers to the UH Event Response Expedition

Current Geologic Activity and Research at Loihi

DETAILED UPDATE PAGES:
2001	early '98	Late '97	early '97	Nov '96	Oct '96	Aug-Sept '96	mid Aug '96	early Aug '96	July '96

Visit these Recent Activity Links Too:

The largest swarm of earthquakes ever recorded on ANY Hawaiian volcano recently occurred at Loihi seamount. It began on 17 July 1996, and to date, a total of over 4000 earthquakes have been recorded by the Hawaii Volcano Observatory (HVO) network, with more than 40 earthquakes between magnitude 4 and 5 recorded by the World Wide seismic network.

Activity apparently moved up the south rift during the first day or two to the southern summit region, which is the oval-shapped region colored in light blue and pink hues in the image on the main Loihi web page. This summit platform area is at 1200 to 960 m below sea level.

Here is a map showing Recent Hawaiian Earthquakes as of 31 Aug 1996, including those at Loihi (color-coded by date of earthquake).

This image created by Jackie Caplan-Auerbach at UH. Click on the image to see a full-scale view.

Because the HVO seismic network is too far from Loihi to detect harmonic tremor (which is associated with the movement of magma), we were unsure about the cause of this earthquake swarm: it could be tectonic or volcanic. An expedition was organized to investigate things further, given our poor constraint on the cause of these unprecedented events:

Some hypothesized possible causes for this unprecedented earthquake swarm are:

Volcanic
- Effusive eruption (normal Hawaiian-style)
- Explosive eruptions (rare in Hawaii, last seen in 1924)
Tectonic
- Pit crater collapse (Kilauea had one in the 1920's)
- Caldera collapse (Kilauea had one in 1790)
- Landslide (these are rare in Hawaii and usually are associated with even larger magnitude quakes)
Some combination of Volcanic and Tectonic

The long duration of the swarm event and the moderate magnitude of the quakes are most compatible with either a pit crater collapse or an explosive eruption origin. However, we have never witnessed (directly or remotely) a Hawaiian submarine effusive eruption so it is possible that this could be one.

Please see the other Loihi pages for post-expedition results and how they bear on the hypotheses above

UH Scientists Fred Duennebier, Mike Garcia and Ken Rubin provided information used on this WWW document.

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Last page update on 18 Sept. 1996