2000 UTC 09 April, 2007

Discussions with HF radio operator at Ranogga Island yesterday confirmed dramatic uplift of Ranogga with initial estimate of a widespread rise of 10 metres, resulting in the existing canoe landing and small harbour at Buri Village now landlocked, and widespread dieoff of coral and reef llife. Continued fears of further seismic and tsunami activity, coupled with the stench of the dying reef biota has dictated residents remaining on high ground in the bush.

Radio operator at Simbo Island yesterday confirmed massive subsidence of large areas of coastline on what was an island dominated by shoreline villages. This permanent loss of large areas of coastal land, coupled with local fears of an imminent eruption of Ove volcano, has led Simbo communtiy leaders to petition the Governor-General [who visited Simbo by helicopter over the weekend] and their National Member of Parliament Francis Billyhilly to petition the National Governement to assess the possibility of relocating the entire population of Simbo Island to a new island home elsewhere in the Western Province.

Reports on local radio broadcaster SIBC suggest there may also have been major coastal uplift in the Shortland Islands, where reliable information on effects of the quake and tsunami have not yet been collated.

Causes

The Western Solomons are a textbook example of island arc volcanism, and along with the Russell Group and Savo [a dormant volcano and thermal field], lie along the Greater Melanesian Arc, produced by the convergent plate boundary that lies just to the SW of the chain [Simbo Island being on the opposite side of the boundary], refer to generic diagram below.

Here the Australian Plate is being subducted under the Pacific Plate on a NW-SE axis [Wilderness and Peava Village are on Gatokae Island facing the opposite direction - see website 'locators' page]. There is also a third player, the Solomon Sea Microplate, meets the boundary of the main plates with it's associated spreading centre forming a triple-plate junction. There is continual and complex movement all along this plate boundary, and every now and then the incremental movement gets hung up and subsequently releases with a lurch, producing seismic activity and changes in the seafloor and adjacent islands.

diagram showing the main plate boundary - courtesy Mike Petterson of the British Geological Survey

Graphic evidence of the uplift occurring at the edge of the Pacific plate has been provided at Ranogga, where part of the western coastline adjacent to Buri village has been permanently raised tens of metres by Monday's quake producing large areas of new land. Residents of this area have actually remained up in the hills days longer than necessary as they assumed the sealevel had gone down and they expected it to subsequently rush back, when in fact that whole part of the island has been permanently raised and new land created.

At Simbo Island, situated on the leading edge of the Australian Plate on the opposite side of the plate boundary from Ranogga and the rest of the Western Province, the opposite is occurring with people afraid to come down from the hills [have spoken with them again this morning] due to what they describe as a continual 'high tide' - there has in fact been extensive subsidence as the leading edge of the Australian Plate is further subducted under the Pacific Plate in one jolting movement, with land being covered permanently by sea. In those affected areas there is still the possibility of subsequent large quakes and resultant tsunamis. The two islands are only a couple of km apart but on different tectonic plates.

The abovementioned convergent plate boundary produces fore-arc volcanism, where magma from the earth's mantle intrudes into the earth's crust on the uplifted side of the plate boundary. This is what currently feeds Kavachi submarine volcano just 30km from the plate boundary. In the distant past this fore-arc volcanism was responsible for the formation of the chain of islands just to the northwest - Mere Island, Gatokae, Vangunu, New Georgia and Kolombangara. In a geologic period of time, Kavachi too will likely become a similar, classic rainforest-clad volcanic peak thousands of feet in height, and replaced by new submarine volcanoes to the southwest.

graphic courtesy of Volcano World

(Please note I am not a volcanologist, seismologist, or plate tectonics expert, so these are quick, lay descriptions only! Thanks to Mike Pettersen who has helped explain the nuts and bolts of it all over the years. Google can provide considerable detailed, and in some cases accurate [nobody else visits Kavachi for example so hard data is scarce], descriptions of the mechanics of this activity. Any contributions in the form of accurate information from the affected areas, or material that helps paint a better picture of what has happened, as you all know we don't have internet or any other media acces here except SIBC, pls email to us here at wilderness@uuplus.com , note our satellite email can handle only a limited amount of large files, max 100kb compressed. Thankyou!)

Kavachi Submarine Volcano Assessment

After receiving several speculative reports from Gatokae and Vangunu people of noises attributed to Kavachi Submarine Volcano [20 nautical miles to our west-south-west] and a confirmed report from Marila Timi of Biche Village of Kavachi emitting an eruption column visible from her garden above Biche, we were fortunate in having Paul and Robyn Hesling of Honiara and friends charter the Wilderness longboats to go out on our organised 'Kavachi Tour' yesterday Friday April 6.

Departing Wilderness the weather was fine with a light westerly wind, moderate windchop and 2 metre southwest swell, the trip out took 2 hours. We spent 2.5 hours on location within 200 metres of the vent, and I freedived down to within tens of metres of the vent. The volcano was doing it's usual vigorous upwelling, producing a plume of discoloured mud and sulfur-laden water several hundred metres wide and at least 3km in length downcurrent, I freedived in and around this plume and the composition and temperature [~40C] appeared normal as compared with my previous 30 visits to Kavachi since 1999. The only explosive activity observed/felt was occasional thudding detonations and and sea-surface percussions, shockwaves producing spray and billows of ash-laden water, but no significant explosive eruption columns or signs of pryroclastic materials as observed on many previous visits. Overall, nothing out of the ordinary observed as a result of the nearby quakes of the last few days, contrary to local anecdotal reports and predictions, and only a moderate level of activity.

Past experience has graphically illustrated the mercurial nature and sheer unpredictability of Kavachi, going from weeks of continual gentle upwelling [a near constant phenomena over the 7 years of monitoring] to an explosive magma-laden eruption column a hundred and fifty metres in height in the space of a second. Similarly I have freedived and sounded the vent at 20 metres underwater, only to return a few days later to see an island 10 metres high complete with lava lake and continual explosive eruptions, and return two weeks later again and the vent is 30 metres underwater, a dynamic and dangerous piece of seafloor to say the least......three images of yesterday's visit appear below, images of previous Kavachi eruptions can be found on the 'Kavachi' page in the image gallery of this website [which will soon be updated with larger format pics from the archive].

Compiled by Corey Howell at The Wilderness Lodge, Peava Village, Gatokae Island, Western Province, Solomon Islands

W: thewildernesslodge.org

E: wilderness@uuplus.com