Mount
Erebus - Antarctic Volcano
The volcanic activity at Mount Erebus has been of interest ever
since Shackleton's men scaled the peak in 1908.
The Mount Erebus Volcano
Observatory (MEVO) a year-round interdisciplinary network of instrumentation
that includes seismic, GPS, infrasonic, and weather
measurements monitors eruptive events of the volcano and the movement
of lava in and beneath the summit crater. MEVO sends its data to
McMurdo station and from there uses the McMurdo Internet to forward
it to scientists at the New Mexico Institute of Technology, to the
UNAVCO geodetic consortium, and to the larger geophysical community.
(MEVO
Website)
|
Shackleton
Meets the Volcano
|
|
The craters of Mount Erebus were first
visited in March 1908 by members of Shackleton's expedition,
who initially noted the "vast abyss" filled with great masses
of steam that rose in a column 150 to 300 meters high. During
a brief clearing, they observed the crater and noted the steam
explosions issuing from three well-defined openings at the
bottom of the high cauldron. As recorded in the book by Shackleton
(1909) the party also observed around the summit area "lumps
of lava, large feldspar crystals, from one to three inches
in length, and fragments of pumice; both feldspar' and pumice
were in many cases coated with sulfur."
|
Field
studies on the volcano include analysis of lava bombs and other
forms of volcanic ejecta resulting from degassing explosions in
the lava lake. Other
studies of Mount Erebus have included core drilling into the rocky
flanks of the volcano to determine the types and sequence of materials
erupted and monitoring of seismic wave activity. Of particular interest
has been the discovery of several layers of ice interbedded with
lava flows, which indicates that in the distant past lava eruptions
occurred over glaciers without completely melting the ice.
The inner crater is situated
in the northeastern part of the outer crater, and the lava lake
and most eruptive activity are confined to its northern half.
Mount Erebus supports a broad glacier
system, with, most ice sheets extending to the edges of the
island.
Termini either form abrupt cliffs which
discharge ice to the marine waters of the Ross Sea on the
north and west, or they merge gently with the Ross Ice Shelf
along the eastern coastline.
Of particular interest is the Erebus Glacier
Tongue, an elongate, serrate-edged lobe of ice that extends
for several kilometers into Erebus Bay of McMurdo Sound, where
most of it floats in water as much as 400 meters deep. The
glacier is 50 to 300 meters thick and lengthens about 160
meters a year.
|
Lava issues from the
northeastern edge of the crater and flows slowly along a curved
path before disappearing into a tunnel-like opening at the south
edge of the lake. Degassing explosions in the lake eject lava bombs
over the southern half of the inner crater and occasionally
onto the floor of the outer crater. Strong eruptions from the crater
have thrown bombs as high as 1000 meters and 700 meters laterally,
onto the snow surface outside both craters.
The crater topography
is much more rugged than expected from observations below, with
some ridges more than 30 meters high, and with strange formations
of ice rising above fumerole areas--the products of steam condensing
and freezing immediately into some extraordinary structures which
rise here and there above the surface of the snowfield. 
The lava lake may be
a periodic, occurrence, depending on the degree of volcanic and
thermal activity in the crater. According to geologist Robert Forbes,
when he observed the crater during Operation Deep Freeze in 1955,
it contained only solid rock fragments. In 1974, a party of New
Zealand Scientists spent several days at the summit, on one occasion
rappelling into the inner crater for the purpose of collecting a
sample of the molten lava. During the roped descent, gases within
the lava caused ejections of small bobs of liquid rock, which splattered
around the climbers and their camp; they beat a hasty retreat from
the summit area.
|
Fire and
Ice
|
|
Ross Island is entirely volcanic in origin
and is formed by four principal volcanoes-Mounts Erebus, Terror,
Bird, and Terra Nova-as well as numerous smaller volcanoes
and lava flows.
Of the volcanoes, only Erebus remains
active. At 3794 meters, Mount Erebus is the highest point
on Ross Island and the largest, most active volcano on the
Antarctic continent.
It is almost always observed with a cloud
of vapor rising from its summit crater.
Much eruptive and seismic activity has
been observed, including ejections of volcanic bombs as much
as 8 meters across.
At the summit, a l00-meter-deep outer
crater about 650 meters across contains a similarly deep inner
crater about 250 meters across, in which lies a lake of red,
molten lava.
|
|
