The southernmost and largest of the two shield volcanoes forming Grand Comore Island
(also known as Ngazidja), Karthala contains a 3 x 4 km summit caldera generated
by repeated collapse.
Elongated rift zones extend to the NNW and SE from the summit. The lower SE rift zone
forms the Massif du Badjini, a peninsula at the SE tip of the island. Historical eruptions have modified the morphology of the compound, irregular summit caldera.
More than twenty eruptions have been recorded since the 19th century from both
summit and flank vents. Many lava flows have reached the sea on both sides of the island,
including during many 19th century eruptions from the summit caldera and vents
on the northern and southern flanks. An 1860 lava flow from the summit caldera reached
the western coast north of the capital city of Moroni.
Monday, April 18th 2005 at 14.30 UTC
Karthala erupted early on Monday, sending thousands of people fleeing from their homes
at the urging of the government. Lava started flowing out of the 2 361m Mount Karthala at
1.30am (22:30 GMT), just hours after the volcano spewed ash and dark smoke. There were
no immediate reports of injuries. Government officials say some 10 000 people have been
affected by the eruption.
Monday, April 18th, 2005 AT 08.00 utc
Hundreds of villagers fled the slopes of Karthala today as fumes belched from the crater and
black rain pounded houses, sparking fears of an eruption. According to one resident of
Idjinkoundzi on the western flank people are in total darkness, gritty rain is falling
and visibility is zero.
Frightened families from the villages of Trelezini and Tsorale piled
into taxis and buses and
Vulcanologists at the archipelago's Centre for Documentation and
Scientific Research said the activity did not necessarily imply the
volcano would spew rivers of lava, one of the more destructive scenarios
in the event of an eruption.
September 21st, 1972
Karthala . . . started new eruption 8 September 1972. Rapidly built up cinder cone at
northern end caldera close to Porte D'Itsandra. Still quite active with boiling lava lake.
Early flows emitted about 2,300 m above sea level rapidly reached altitude 1,500 m
and stopped. Further yet narrower flows presently running over early ones.
No immediate danger foreseeable for either capital city of Moroni or airfields."
April 17th, 1977
Lava extrusion during 5-10 April eruption destroys three villages. The eruption began at about
noon on 5 April from a SW flank vent, after a series of local tremors during the morning.
Basaltic lava was extruded, which divided into two flows ~300 m wide and 3-15 m thick,
separated by several hundred meters. The flows reconverged downslope and reached
the sea on 6 April. Strong earthquakes were felt on the SE flank on 8 April, but were not
accompanied by surface activity. Lava extrusion had ended on 10 April, although heavy fuming
from nearby fissures continued as late as 17 April, preventing close approach to the vent,
which was surrounded by up to 6 m of lapilli. No casualties were reported,
but 4,000 people were evacuated and three villages damaged or destroyed.
July 11th, 1991
Seismic swarm precedes phreatic explosion; press reports of ash/lava eruption incorrect .
Widely distributed news reports of ash and lava emission during the evening of 2 July
proved incorrect. As of mid-July, the only documented eruptive activity had been a
phreatic explosion on the 11th. According to the press, some villages around the base of the
volcano were evacuated, but many fewer residents fled than the tens of thousands initially
reported. (Comes to my mind that this isn't the first time false reports have been posted...).
The eruption followed three months of increasing seismicity monitored by a joint group from the
Centre National de Documentation et de Recherche Scientifique des Comores (CNDRS),
the Univ de la Réunion, and the IPGP.
The following is from their report.
"At 1645 on 30 June a seismic crisis began with events centered below the S part of
the caldera and the volcano's S flank. During the night of 30 June, many shocks were felt by
residents of the SW part of the island. Seismic activity continued 1-2 July, with both short-
and long-period events occurring at average rates of 60-100/hour. Some of the short-period
events reached M 2.5-3. One M 3.1 earthquake (at 0708 on 2 July) was felt in the SE part
of the island (in the Foumbouni area). This intense seismic activity has caused many people
living in the SW to move to Moroni, the capital and island's largest city.
"The seismic crisis continued until 10 July, with the number of earthquakes reaching 250/hour.
After several hours of relative calm, a phreatic eruption occurred at 0330 on 11 July,
after which the number of earthquakes returned to ~100/hour. During overflights of Choungou
Chahalé Crater (summit area), it was observed that the rim of the S half of the summit
caldera was covered by ash and blocks of old material. The crater was filled with gas that
stagnated in its bottom. A sound like a lava fountain was audible, but no lava fountain was visible.
Seismicity continued to increase from 4 July, with 4,000 earthquakes recorded daily by 10 July.
A swarm of nearly continuous seismic events was recorded between 0040 and 0110 the next day.
The 4-10 July seismicity was characterized by low-magnitude, short-period events located
under the summit at 1-4 km depths, and less numerous deeper earthquakes at 4-8 km depth.
Later visits to the summit revealed that a sizeable phreatic explosion had occurred in
Choungou-Chahalé crater. The southern 2/3 of the summit caldera were covered by blocks
(up to 10 m3) and ash, and the summit vegetation was completely removed from within the
limits of the caldera. The crater bottom was hidden by gas and vapor clouds, obscuring the
source of a "fountaining" sound heard two weeks after the 11 July explosion.
Search this site - Søk våre sider