Volcanoes of the Solomon Islands – Part 1 of 2

Map of Solomon Islands and most of its volcanoes. Two active volcanoes are in yellow, Kavachi, center left, and Tinakula, lower right. Recently active volcanoes are in bright green. Dormant / extinct volcanoes are black. Bougainville Island in the upper left is part of Papua New Guinea, but also volcanic. New Georgia Island group center left is home to most of the volcanoes to be discussed in this post. Image screen capture from interactive map in Volcano Discovery

The Solomon Islands is a collection of six major islands and over 900 smaller islands in Oceania east of Papua New Guinea (PNG), NW of Vanuatu.  It has a population of just over 650,000.  The islands have been populated for at least 30,000 years, with multiple waves of more recent immigrants.  The first western discovery was by a Spanish explorer in 1568.  The islands became a British Protectorate in 1893.  There were extensive battles during WWII in the Solomons between Japanese, American and British military forces.  The islands became independent and self-governing 1975 – 1978.  The form of governance is a Constitutional Monarchy.

Tourist map of central Solomon Islands and travel routes into and out of the nation. Image courtesy Visit Solomons.com

The islands are volcanic, with at least 10 resident stratovolcanoes and 5 submarine volcanoes.  Granyia wrote an extensive 2017 post about Tinakula, an island stratovolcano which erupted in Oct 2017 located in the Santa Cruz Islands, on the far eastern end of the Solomons.  This time around, I will touch on a few of the other recently active volcanoes among the islands.  This is by no means a comprehensive list, as previously unknown submarine activity is being discovered every time someone conducts an oceanic survey in the Solomons.

Three of these volcanoes are currently active, the previously mentioned Tinakula, Savo and Kavachi.  Two others, Simbo and Nonda have active solfataras.  Since discovery by the Spanish, three of these volcanoes have had eruptions in the VEI 2 – 3 range, Savo, Tinakula and Kavachi.  The deadliest of these was a VEI 3 from Savo that killed over 1,000 in 1568.  Kavachi is a currently active submarine volcano that periodically builds ephemeral islands that quickly return back below the ocean surface.

Map of Santa Cruz Islands in far eastern section of the Solomon Islands. Image courtesy Wiki

This post will take a closer look at Cook, Savo, Kavachi, and Nonda. 

The distance between the westernmost and easternmost islands is 1,500 km.  The Santa Cruz Islands, are N of Vanuatu, and are separated from the rest of the islands by 200 km of ocean.  To the W, Bougainville is geographically part of the Solomon Islands, but politically part of PNG.  It also has multiple volcanoes.

Solomon Islands showing surrounding reefs. Image courtesy Oceana Expeditions

The climate is humid and tropical.  Jun – Aug is typically a bit cooler.  Nov – Apr has more frequent rainfall, with the total averaging over 305 cm yearly.  There is also the occasional cyclone.  The islands are typically covered with tropical rain forests.  Soils range from very fertile and productive volcanic soils to limestones from corals. 

Agricultural economic activity includes timber exports, palm oil exports, copra and cacao.  There is mining on Guadalcanal.  There is commercial fishing, tourism, and diving. 

Sadly, there was also ethnic violence and civil unrest 1998 – 2003.  The Solomons government was described a not a failed state, rather an unformed one.    

New Georgia Islands group. Major volcanoes are clearly visible on the islands. At least two seamounts are visible lower center left, just SW of the trench line which cuts the SW third of the image. Screen capture from Google Maps

The volcanoes are generally remote and typically monitored the old-fashioned way, by passing mariners and planes.  There volcanic front has migrated SW over the eons, with 12 recently active volcanoes (surface and undersea) concentrated around the New Georgia Islands.  This island grouping includes Vella Lavella, Ranongga, Kolombangara, New Georgia, Rendova, Vangunu and Nggatokae Islands.  Active volcanoes in this part of the Solomons are migrating to the SW into the ocean with at least four currently and recently active volcanoes.  Vogripa does not list any of the Solomons volcanoes with massive known eruptions, which may say more about the remoteness of the Solomons than anything else.  The region also has massive earthquakes due to the complex interaction of subducting and jostling microplates.

Heavily eroded cone of Maetambe Volcano on central Choiseul. Volcano is at the center of the image, just a bit SE of the island name in white. Screen capture from Google Maps

Volcanoes – Listed generally from NW to SE

Maetambe Volcano – Choiseul Island

Maetambe volcano is located on Choiseul Island, closest major island to Bougainville Island, PNG.  It has what appears to be relatively recent ash flows.  These have been dated to be a bit older as Pliocene to Pleistocene in age.  Volcano Discovery lists this as probably extinct, with no eruptions in the last 10 ka.  The volcano may be as old as 2.6 Ma.  Note that the volcanic front in this part of the Solomons has migrated SW. 

Paraso thermal area on Nonda volcano, Vella LaVella Island. Image courtesy M Petterson, Jan 2016

Nonda Volcano – New Georgia Islands

Nonda is the youngest volcanic feature on Vella Lavella Island some 80 km SSW of Maetambe.  It is a lava dome inside a well-preserved crater.  There are no known historical eruptions, though inhabitants reported smoke and explosive activity around the time of a major earthquake in 1959.  The island has several fairly recent, overlapping volcanic centers.  The Paraso thermal area on the island has solfataras, hot springs, and boiling mud pots.

Satellite view of Vella Lavella Island oriented generally to the NE. Neighboring Kolombangara volcano and island clearly visible upper right corner of the image. Nondo volcano is the volcano with the breached cone emptying to the NE. Image courtesy Wikimapia

Vella Lavella Island is a volcanic island surrounded in many places by a coral reef.  The highest elevation is Mount Tambisala at 790 m.  Nonda is 750 m.  Smaller rivers on the island draining the flanks of the volcanoes allow residents to irrigate crops.  Villages are almost exclusively on the coast.  The island is wet, tropical and prone to earthquakes and cyclones.  Excavations have found pieces of pottery dating as old as 3,000 – 2,000 years.  There was active fighting on the island during WWII, including a major naval battle in 1943.  Following the battle, the US Navy developed an airfield on the island used by VMF214, the Black Sheep squadron led by “Pappy” Boyington. 

Kolombangara Volcano – New Georgia Islands

Kolombangara is a relatively new stratovolcano some 60 km SE from Nonda in the new Georgia group of islands in the south central Solomons.  It forms an almost circular 30 km diameter volcanic island.  Its summit has a 4 km diameter caldera breached to the SE.  The island has around 80 rivers and streams draining its flanks.  There are young scoria cones on its western and NE flanks and hot springs near the peak on the southern side of the island.  There are no known historic eruptions from this volcano and last eruption date is unknown.  It is considered to be an extinct volcano by the Solomon Encyclopedia. 

Topographic map of Kolombangara Island looking generally to the NW. 3D representation of the island via Go Tours Travel

The volcano itself tops out at 1,800 m, among the highest volcano on the Solomons outside Guadalcanal.  While the island has been logged, a conservation area was set up in 2008.  There is no logging above 400 m on the volcano.  Visitors hike to the volcanic crater, birdwatch, enjoy the jungle and snorkeling in the coral reefs surrounding the island.  There are guesthouses and lodges that cater to visitors.  Over the course of the last century, residents have abandoned village and burial sites on the mountain and settled close to the coast. 

Possible representation of what the reported eruption of Cook Volcano looked like in 1964. No photos exist of the Cook eruptions, so I borrowed this photo of Kavachi to be discussed later as an example. To reiterate, this is Kavachi rather than Cook. Image courtesy Eyos Expeditions, July 2014

Cook Volcano – New Georgia Islands

Cook volcano is a possible submarine volcano in the western Solomons, around 30 km S of Kolombangara.  It was reported by the HMS Cook in 1963.  There was an eruption that breached the surface observed in May 1964, creating a “mountain of black water,” discolored water, and pumice clasts that washed ashore on neighboring Munda Island.  This volcano is not accepted as part of the Smithsonian GVP database.  Two eruptions from this volcano were reported in 1964 and 1991.  Both were reported by the Australian navy.  The second eruption created a small ephemeral island.  Activity continued for a couple weeks in May 1991.

Cook was originally marked on a British Admiralty chart as a 36 m deep shoal after the survey vessel, HMS Cook reported an uncharted submarine disturbance including a sulfur smell Dec 1963.  The disturbance took place a few kilometers off Munda Point on southern New Georgia Island.  The shoal itself was detected at night using what today would be viewed as primitive, backup depth sounding equipment.  A strong earthquake took place in the same general area some 20 days later.  May 1965 two villagers in a canoe saw a large mass of water rise from the same general area and fall back into the sea.  Detailed marine geophysical surveys in 1979 and 1981 failed to detect anything large enough on the sea floor in the region to have a summit at 36 m below the surface.  Current speculation is that the disturbances might have been hydrothermal system blowouts from the sea floor 1,300 m below the surface, perhaps related to seismic activity and sea floor faulting.  Chapter 11 of Fire Mountains of the Islands concludes that Cook volcano may be a modern myth.

Saltwater Lake Ove in the foreground from the rim of Ngusunu crater on the W coast of Simbo island. Image courtesy Chris Lyne, 2005, via Smithsonian GVP

Simbo Volcano – New Georgia Islands

Simbo is a small island in western Solomons some 70 km SW of Kolombangara.  Simbo Island is actually two islands, the small one known as Nusa Simbo, and the larger one as Simbo (Mandegugusu).  The active volcano is locally known as Ove and tops out at 335 m.  It has a string of three truncated andesitic volcanic centers.  The volcanoes date around 2.3 Ma, though there are native accounts of explosive eruption and enlargement of the Ngusunu crater on the SW coast of the island around the turn of the 20^th century.  There are press reports of activity that forced evacuation of villages close to the crater due to volcanic activity in the early 1900s.  A M 8.1 nearby earthquake to the N in 2007 sent a 12 km tsunami onto Simbo Island that destroyed two villages on the northern side of the island and killed 10 residents. 

Fumarole region on the side of Simbo volcano. Note the sulfur laced on the slope and the lack of anything growing on the hot area. Image courtesy Solomon Star News, Feb 2015

The southern half of the island is thermally active with fault related fumarole areas and hot springs near saltwater Lake Ove on the western coast near Mount Patukio.  The lake’s waters are a mixture of reds and yellows, with a trace of sulfur in the air.  There is an undersea geyser near the shore which will occasionally blow a steam column through the surf.  There are fault related fumarole areas and hot springs along the western coast and along the eastern coast near Mount Patukio.  A 1945 visit observed megapodes dig burrows and lay their eggs on volcanically warmed soil.  Although the eggs are buried up to a meter below the surface, they are considered local delicacies to the point where residents have decimated megapode populations on Simbo and Savo by taking too many of them.

Seaside thermal vents on Simbo Island. Image courtesy Kerrie Kennedy, Flickr, Jan 2005

Volcanic activity for Simbo, Kana Keoki and Coleman seamounts is driven by the subduction of the Woodlark spreading center beneath the Pacific Plate / Solomons Block.  This reoriented around 2 Ma, fragmenting into a series of short ESE trending segments.  The segments continued to spread until around 0.5 Ma.  The Simbo transform propagated northwards along the W side of the trench, forming a trench-trench triple junction that leaked sufficient mantle fluids to build Simbo Ridge.  As the Pacific Plate approached, the area E of northern Simbo Ridge tilted northwards, sheared, elevated, and allowed arc-related magmas sourced beneath the Pacific Plate to build three large stratovolcanoes on the subducting Indo-Australian Plate, Simbo at the northern end of the Simbo Ridge, Kana Keoki and Coleman seamounts on the SE end of the Ghizo Ridge. 

View across the ocean toward Rendova Volcano and Island. Image courtesy ABC News, Sept 2019

Rendova Volcano – New Georgia Islands

Rendova island is a Pliocene to Pleistocene basaltic volcano on Rendova Island, some 44 km SE of Cook.  It created the northern half of the island.  The cone is well eroded and has no known recent eruptions.  The most recent eruption is older than 10 ka.  The volcano is younger than 2.6 Ma.  It is a basaltic volcano.  The southern part of the island consists of uplifted submarine lavas.  It is considered to be an extinct volcano by the Solomon Encyclopedia. 

Next

Part 2 will be posted in two weeks. It will cover the remaining volcanoes, tectonics and conclusion. I am reproducing the Additional Information section in both posts.

Additional information

WorldData.info – Volcanoes on the Solomon Islands

Volcano Discovery – Volcanoes of the Solomon Islands (16 volcanoes)

WOVO.org – Honiara Solomon Islands

The eruptive history and volcanic hazards of Savo, Solomon Islands, Petterson, et al, 2003

Smithsonian GVP – Kavachi

Fire Mountains of the Islands – 11.  Cooke-Ravian and a Volcanic Resurgence: 1971 – 1979

Exploring the “Sharkcano”: Biogeochemical Observations of the Kavachi Submarine Volcano (Solomon Islands), B Phillips, Oct 2016

Oceanography, Vol 26, Number 4 – Exploring the “Sharkcano”, Phillips, et al, 2016

The elusive Cook volcano and other submarine forearc volcanoes in the Solomon Islands, Exon, et al, 1986

Kavachi, and active forearc volcano in the western Solomon Islands reported eruptions between 1950 and 1982, Johnson and Tuni, 1987

Global tectonic significance of the Solomon Islands and the Ontong Java Plateau convergent zone, Mann and Taira, Oct 2003

Post 8 Ma reconstruction of Papua New Guinea and Solomon Islands:  Microplate tectonics in a convergent plate boundary setting, Holm, et al, Mar 2016

The role of slab melting in the petrogenesis of high-Mg andesites: Evidence from Simbo volcano, Solomon Islands, Konig, et al, Oct 2007  

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