Activity during February 2000. At 1422 on 3 February an ash cloud was
reported up to 4,500 m
over the island. Between 0507 and 0520 on 18 February a Vanair
pilot reported an ash cloud initially as
high as 9 km and then around 4.8 km altitude. A plume was identified
on infrared and early morning visible
satellite imagery, but there was considerable cloudiness in
the area. Activity was continuing as of 0602 on
19 February, with an ash plume to ~5.5 km altitude. Convective
activity through the day rapidly obscured
any traces of the ash plume on satellite imagery. Analyses indicated
that the plume may have contained
significant ash that was expected to move ESE-SE and extend
to 370 km. Due to the convective activity
pilots were advised to respond as though the plume was rising
to ~9 km altitude. However, another pilot
report at 0621 indicated that activity had ceased.
According to John Seach, around
midday on 19 February villagers on the neighboring island of
Paama heard two loud explosions from the volcano; the second
was the loudest heard in two years. This
was followed by a brown ash cloud rising to ~4.5 km altitude
visible from an aircraft en route from Sydney to
Hawaii. Ashfalls occurred on Paama. A pyroclastic flow from
the NW-flank crater (figure x1) traveled 2.5 km
SW and reached the sea along a 300-m-wide front, where it created
a delta. Blocks of 4 m in diameter
were carried down to sea level. A 3-m-diameter block 50 m from
the sea had a surface temperature of
170°C.
Trees buried in the ash were only visible as circular, black
smoking areas when observed on 23
February. On the edge of the pyroclastic-flow deposit trees
0.5 m in diameter were snapped off 2 m from
the ground (figure x2); some were upturned and redeposited in
the ash. Standing devastated trees were
burnt to a height of 18 m and debris was lodged in the canopy.
Some fallen trees were still burning. Within
20 m of the edge of the pyroclastic-flow deposit were fallen
devastated trees, and standing burnt trees were
present for another 10 m beyond that. Observers were forced
back when ground temperatures (over
200°C) melted boots. The air was filled with the smell of
burnt trees and sulphur. Coconuts superheated and
exploded. Sap in smaller branches boiled and formed bubbles
on the outside of the branch.
The active NW crater (figure x3) was climbed by Seach and Geoff
Mackley on 23 and 24 February
2000. A lava dome was present on the SW crater rim from where
the pyroclastic flow had originated along
a 100-m-wide front. Lighter colored deposits marked its track
down the volcano. On the N edge of the
pyroclastic-flow deposit and 200 m below the NW crater was the
source of a debris avalanche. A debris
volume on the order of a million cubic meters had moved, exposing
a large hole and producing two
branching flows that moved ~250 m SW towards the sea. A new
150-m-high cinder cone formed inside the
old crater was smoking with blue and white vapor being emitted.
Ground temperature was 81°C at the base
of the cinder cone. A two-week-old flank lava flow was observed
to have traveled 1.5 km WNW to an
elevation 250 m below the NW crater, burning trees and vegetation.
Additional eruptions during March and April 2000. Another minor
eruption on 15 March sent ash
to 1,500 m, where it mixed with meteorological clouds. A stronger
eruption began on 21 March with ash
reported to 2,700 m altitude along with steam to 450 m. Activity
increased the next day, when the plume
was reported to be at levels of 4,200-4,500 m. The eruption
continued during 23-24 March with plumes
rising to altitudes of about 2,400 m.
A pilot report around 1100 on
24 April indicated a very dark-brown ash cloud rising from the volcano
to an altitude of ~4,800 m and drifting NW. The report also
noted that a new vent on the W side was
emitting lava. A notice to aviators stated that they should
expect ash to 5,400 m altitude within 550 km in the
NW quadrant of the volcano. Ash warnings to aviators in the
late morning and night of 25 April indicated that
ash and lava continued to be emitted from the W vent. Pilot
reports indicated that the height of the ash cloud
was difficult to determine due to cloud cover, but was at least
to 600 m altitude. The ash appeared to be
thinning out beyond 18 km W of the volcano, but the extent of
the plume could not be determined from
satellite imagery. A notice at 2155 on 26 April stated that
no further visual activity reports had been
received since 25 April.
Background. The small 7-km-wide
conical island of Lopevi is one of Vanuatu's most active
volcanoes. A small summit crater containing a cinder cone is
breached to the NW and tops an older cone
that is rimmed by the remnant of a larger crater. The basaltic-to-andesitic
volcano has been active during
historical time at both summit and flank vents, primarily on
the NW and SE sides, producing moderate
explosive eruptions and lava flows that reached the coast. Historical
eruptions date back to the mid-19th
century. The island was evacuated following eruptions in 1939
and 1960. The latter eruption, from a
NW-flank fissure vent, produced a pyroclastic flow that swept
to the sea and a lava flow that formed a new
peninsula on the western coast.
Information Contacts: Wellington
Volcanic Ash Advisory Center (VAAC), MetService, PO Box
722, Wellington, New Zealand (URL: http://www.metservice.co.nz/);
John Seach, PO Box 16, Chatsworth
Island, N.S.W. 2469, Australia (Email: [email protected]).