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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 20th 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.
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.
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.
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.
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.