Tristan, and its neighbouring islands, lies about 400 km east of the Mid-Atlantic Ridge.
The base of the volcano is at 3700 m below sea-level, and the summit is at almost 2100 m
above sea-level. Marine erosion has formed the high, sheer cliffs (the Main Cliffs) that
surround most of the island. Above the Main Cliffs is a more gently sloping region between
600 and 1000 m (the Base).



Rising from the Base is the steep central cone (the Peak) which has a small summit crater.

The Peak predominantly is composed of pyroclastic deposits erupted from the central vent.
The Base and Main Cliffs predominantly are composed of thin basaltic lava flows, commonly
separated by thin pyroclastic layers. There are over 30 cinder cones on the flanks of the main
volcano, many of which have produced small lava flows.


Map from National Geographic, May, 1962 issue.

The October 1961 eruption was preceded by earthquake swarms and rock falls from the
Main Cliffs, then lava was erupted on the plain immediately east of the settlement.
The growing lava mound breached and lava flows were erupted toward the coast.
As the eruption waned, an elongate lava dome grew and sealed the vent.
All above except Nat.Geo.map, from 'Geology of Tristan da Cunha', University of Oklahoma

Tristan Island is a dormant volcano with a lake in the top of the cone which provides fresh
water. In October of 1961 the volcano erupted from a flanking vent next to the settlement
and forced the evacuation of the entire population to Britain where they lived unhappily for
a year. The eruption eventually destroyed the processing plant.

August 7th, 2004

Floating rocks retreived by Tristan's fishermen
© SARTMA

Though all may seem quiet on the surface, the latest seismic information from the Island is
quite different.  Many kilometers beneath the 1961 Volcano the rocks are still shaking. 
Indeed, there has been other seismic activity along the Atlantic Ridge, which has contributed
to this scenario.

The South Sandwich Islands have also experienced seismic activity within the same time-
frame that Tristan did.  No data has been received about the events being related, however.

At the moment, fishermen from Tristan are reporting floating rocks all around the Island. 
(See the photo above)  This is an indicator that the activity could have been on the seabed.
  Tristan da Cunha is located near to the Atlantic Ridge on the African Plate and could
well receive pumice from eruptions on this spreading centre.

According to Tristanians, the 1961 volcano smokes and even vibrates occasionally but no
one pays any attention to it.
Tristan Times and SARTMA - TdC

August 3rd, 2004
A swarm of earthquakes struck Tristan da Cunha on the nights of 28 and 29 July 2004.
Further to reports published earlier on Tristan Times Online, a swarm of earthquakes struck
Tristan da Cunha on the nights of 28 and 29 July 2004.  According to the Preparatory
Commission for the CTBTO Vienna International Centre, the main swarm lasted about
eight hours and was located 30km below the 1961 volcano.

  After the main swarm, there were a few individual earthquakes.  Seismic activity tapered
off since then, however, there has been no report received for 01 August 2004.
According to Tristan Times the appropriate authorities in the UK have been informed,
although no one is thought to be in any danger from this most recent seismic incident.

Latest: There has been a small land slide near the potato patches south-west of the village.

The island passed into obscurity until 1961, on August 6th tremors and rockfalls were felt behind the settlement which became more frequent as the weeks passed. Nobody could explain them and it was thought the heavy rain had caused landslides. At the beginning of October things got worse and a new fissure was found to have opened in the mountain side. The following day the earth tremors got worse as the administrator considered it wise to move the islanders away from the danger zone and the whole population was evacuted to Nightingale Island some 25 miles away. Wearied by a long walk to safety and a cold night spent in sheds and on open ground, refugees set out for the fishing vessel Tristania, which will ferry them to Nightingale Island, one of Tristan's uninhabited neightbors. From National Geographic, May, 1962 issue Examination of the site showed a mound had formed which was increasing in size rapidly and suggested imminent volcanic activity. A ship was scheduled to call at Tristan to pick up half a dozen passenger and was diverted to Nightingale to pick up the 290 residents to take them to Capetown. As they passed Tristan they saw the volcano in full eruption. Main page to the article in National Geographic. From National Geographic, May, 1962 issue The islanders were embarked for England in Capetown and were accomadated at Calshot near Southampton. At the turn of the year passing ships noted the volcano was still erupting and the traditional landing places had disappeared under lava. The eruptions had died by August 1962 and the Islanders voted overwhelmingly to return and in November 1963 they did so. In 1965, a new harbour was built for the re-establishment of the Crawfish Industry and this is now the Island's main industry, together with the sale of postage stamps to collectors and now the island has slipped back into obscurity remote from civilisation. From 'Tristan's History' by John

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