|
About 45 km east of Ta’u, the easternmost Samoan
island (14°13'S; 169°04'W) lies a 4.200m high active,
submerged volcano. In size and appearance, it resembled Mount Fuji in
Japan or Mount Rainier in Washington.
Summit depth 590 metres (1,940 ft)
Vailulu'u is a volcanic seamount discovered by geophysicist Rockne Johnson
in the Samoa Islands on Oct. 18, 1975.
At hot spots,
magma from the mantle bursts through the crust, creating seafloor volcanoes
that often rise above the ocean surface to form islands. Island chains
like Samoa form as overlying crustal plates move over the stationary
injection point of the hot spot.
(Jayne
Doucette, WHOI)
The basaltic seamount, is considered to mark the current
location of the Samoa hotspot. The summit of Vailulu'u contains a 2
km wide, 400-m-deep oval-shaped caldera.
On July 10, 1973, explosions from Vailulu'u were recorded
by SOFAR (hydrophone records of underwater
acoustic signals). An earthquake swarm in 1995 may have been related
to an eruption from the seamount.
Turbid water above the summit shows evidence of ongoing hydrothermal
plume activity.
Evidence released in 2006 suggest that Vailulu'u may
breach the surface of the ocean and officially become an island during
this century.
Nafanua is an active underwater volcanic cone that
has been growing inside the summit crater of Vailulu'u since 2001.
In 2005 it was 300 m tall, but still 708 m below sea level. It is best
known as the site of 'Eel City,'
a hydrothermal vent biological community consisting mainly of eels (rather
than the usual invertebrates).
Source: Partly from
Wikipedia
Bathymetric map of Nafanua and the summit crater of Vailulu’u.
Inset indicates the location of Vailulu’u east of the Samoa archipelago.
Hydrothermal sites include the NMHC, the summit of Nafanua, and the
South Wall Hydrothermal Complex (SWHC). The region colored green within
the crater at depths >800 m indicates the Moat of Death, where the
ocean floor is littered with fish and invertebrate carcasses. Note that
all data coverage is indicated by submersible and ROV tracks. Monitoring
locations include temperature recorders, exposure experiments, and/or
light back-scattering sensors (nephelometers). Time series conductivity–temperature–depth
measurements were made at the NMHC site and NW of the crater.
From
"Vailulu’u Seamount, Samoa: Life and death on an active submarine
volcano"
Proceedings of the National Academy of Sciences Online, www.pnas.org.
|
