Recent Activity at Loihi Volcano
Events in Fall 1997
Current Geologic Activity and Research at Loihi
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Until this week, things had been generally quiet at Loihi after the
seismic and erruptive event of last Summer (1996). Following that
activity, seismicity returned to normal (in the Fall of 1996).
More recently, a manned-submersible
exploration program during August and September of 1997
observed the glistening water of high temperature hydrothermal fluids
issuing from vents within the newly-formed (1996) Pele's Pit and
measured water temperatures of up to 200 C. Also observed were
high temperature hydrothermal mineral deposits (similiar to
those observed on Mid-Ocean Ridge volcanoes) that were unlike
lower temperature materials found previously at Loihi and wide-spread
deposits of young-appearing volcanic sand on the summit.
This week, during the initial deployment of HUGO (Hawaii Undersee Geo
Observatory) a hydrophone on the Loihi summit recorded noises that could
be interpreted as eruption-related. This data is preliminary and until
it and other data can be analyzed more thoroughly, we are reluctant
to make a definite statement regarding the cause of the noises.
Some further details are given below.
- Oct. 13, 1997A hydrophone deployed during the 2nd week of
October (1997) at the
newly-installed Hawaii Undersea Geo Observatory site on the summit
of Loihi began recording intense, thunder-like noises from the summit
region within a day of deployment. These sounds, which were last detected
during surveys in Summer 1996, may be related to a new eruption.
Fred Duennebier, the UH scientist who made this observation, noted that
during this event, little seismic activity was detected on a
seismometer deployed on the
Loihi summit for monitoring purposes. Additionally, since there was only one
hydrophone deployed at the time of event detection, little can be said about
the exact location of the event. Unfortunately, the system stopped
communicating a few days later and won't come on-line again until
submersible dives in Jan 1998. We will present new information
here as it becomes available.
- Sept. 9-13, 1997
Preliminary results from recent submersible dives on Loihi indicate
- Exit temperatures of hydrothermal venting has increase drastically
since last summer, with values over 200 C now being recorded.
- the summit area is covered in places with very young and glassy sand
deposits, some of which have partially obscured the young 1996
Rapid response Cruise breccia deposit discussed below. No young in-place
lava flows have been found so far, although diving at Loihi will continue for
another two weeks.
- Aug 13, 1997 - Final Results of 210Po-210Pb dating of breccia lavas collected during the
seismic swarm indicate:
- Young samples collected during the Rapid Response Cruise (RRC)
were actually erupted BEFORE the event seimicity. Two samples were
dated and we have determined that they erupted in February-March 1996
and May-June 1996.
- Although the dates do not coincide with the seismic swarm, it is still
possible that there was a summit eruption at this time and that sub
divers simply didn't find the new flows due to the murky waters.
- No unusual seismicity was observed at Loihi during the spring of 1996,
indicating that the HVO network "missed" the earlier eruptions (and possibly
other small eruptions on Loihi in the past). However, a seismometer
deployed during the RRC recorded 40 times as many quakes after the swarm
as were seen by HVO. Thus, lack of detection by HVO does not invalidate
the measured lava ages. Also, this illustrates the need for a permanent
seismic station on Loihi itself.
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Last page update on 11 Jan 1998