Manus Island, Papua New Guinea, inundated with pumice following eruption of Titan Ridge submarine volcano.

A series of eruptions from the Titan Ridge submarine volcano, beneath the Bismarck Sea in the southwest Pacific Ocean, has produced a large volume of pumice (a light volcanic rock, produced by the rapid cooling of gas rich lava from submarine eruptions, which can float on the sea), much of which has washed up onto the shores of Manus Island, the largest of the Admiralty Islands and a province of Papua New Guinea. This has caused serious problems for the local population, as it has formed a barrier between them and the sea, too dense to push a boat through, but too quicksand-like to walk across. This in turn has prevented them from harvesting fish and other seafood, the main staples of the island, as well as forcing them to become entirely dependent on the islands limited supply of freshwater for washing and hygiene, rather than bathing in the sea. The large accumulations of pumice are also likely to have smothered local coral reef ecosystems, harming longer-term fishing prospects in the region.

Residents of Manus Island on a beach covered by pumice. ABC.

Pumice forms when hot lava from submarine volcanic eruptions encounters seawater and cools rapidly, simultaneously crystalising and degassing to form a lightweight volcanic rock with many gas filled vesicles (bubbles) within it, which often floats on the sea surface. Big submarine eruptions can produce large volumes of pumice, forming rafts of pumice that cover hundreds of square kilometres, and drift on the ocean surface for months before dissipating or washing ashore. 

Titan Ridge, also known as the Central Bismarck Sea Volcano, is located about 125 km to the southeast of Manus, on the northern edge of the South Bismarck Plate. It is located on the boundary between the Willaumez Transform Fault and an unnamed section of area of seafloor spreading, where the South Bismarck and Pacific plates are being pulled apart, while at the same time the Pacific Plate is moving to the west and the South Bismarck Plate to the east. Here fresh material from the upper mantle is rising up through the fault and being erupted from the volcano as volcanic material, primarily pumice caused by the rapid cooling of a liquid melt containing dissolved gasses. 

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Magnitude 6.8 Earthquake beneath the Hubbard Glacier on the border between Alaska and Canada's Yukon Territory.

The Alaska Earthquake Centre recorded a Magnitude 6.8 Earthquake at a depth of 3 km, beneath the Hubbard Glacier on the border between Alaska and Canada's Yukon Territory, slightly after 11.40 am Alaskan Standard Time (slightly before 8.40 pm GMT) on Saturday 6 December 2025. Earthquakes Canada recorded the same event as a Magnitude 7.0 Earthquake at a depth of 10 km. There are no reports of any damage or casualties associated with this event, but people have reported feeling it over a wide area of eastern Alaska, the Yukon, British Colombia, and parts of Washington State.

The approximate location of the 6 December 2025 Hubbard Glacier Earthquake. USGS.

Alaska lies on the North American Plate, with the Pacific Plate underlying the ocean to the south. The Aleutian Trench runs along much of the south coast of Alaska, with the Pacific Plate being subducted beneath this and passing under Alaska as it sinks into the Earth. Off the coast of southeast Alaska the Pacific and North American Plates pass one-another horizontally, with the Pacific Plate moving northward and the North American to the south (a transform plate margin). This is not a smooth process, and the plates frequently stick together, then break apart as the pressure builds up, causing Earthquakes.

How the subduction of the Pacific Plate beneath the North American Plate fuels the volcanoes of Alaska. Alaska Volcano Observatory.

Witness accounts of quakes can help geologists to understand these events and the rock structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) you can report it to the United States Geological Survey here, or Earthquakes Canada here.

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Magnitude 7.0 Earthquake off the coast of Northern California.

The United States Geological Survey recorded a Magnitude 7.0 Earthquake at a depth of about 10.0 km a little  over 50 km off Cape Mendocino in Humboldt County, California, slightly before 10.45 am local time (slightly before 6.45 pm GMT) on Thursday 5 December 2024. There are no reports of any casualties associated with this event, but the size and location of the Earthquake led to a tsunami being issued, advising about half a million people in California to seek high ground (in the event no tsunami was recorded), and minor damage to highways and buildings were recorded in several places, as well as disruption to power networks which left about 10 000 people in Humbolt County without power. The initial Earthquake has been followed by a large number of aftershocks, with the USGS estimating there is a 5% chance of another quake with a Magnitude of 6.0 or greater occurring in the same area within a week, and a 34% chance of a quake with a Magnitude of 5.0 or greater occurring.

The approximate location of the 5 December 2024 California Earthquake. USGS.

California is extremely prone to Earthquakes due to the presence of the San Andreas Fault, a tectonic plate margin that effectively bisects the state. The west of California, including Santa Barbara and Los Angeles, is located on the Pacific Plate, and is moving to the northwest. The east of California, including Fresno and Bakersfield is on the North American Plate, and is moving to the southeast. The plates do not move smoothly past one-another, but constantly stick together then break apart as the pressure builds up. This has led to a network of smaller faults that criss-cross the state, so that Earthquakes can effectively occur anywhere.

Goods knocked from shelves in Hoby's Market & Deli in Scotia, California, following a Magnitude 7.0 Earthquake on 5 December 2024. Dylan McNeil/The Times Standard/AP.

However, the 5 December 2024 Earthquake happened close to the southern part of the Mendocino Fracture Zone, a westward extension of the San Andreas Fault, where the Gorda Plate to the north is moving westward relative to the Pacific Plate to the south. Along this boundary the rocks of the two plates continuously stick together, then become stressed as the motion of the two plates draws them apart. This stress builds up until the rocks are forcibly snapped apart, which we experience as Earthquakes.

A crack is seen on Blue Slide Road in Rio Dell, California, following a Magnitude 7.0 Earthquake on 5 December 2024. City of Rio Dell/ABC News.

The Gorda Plate, along with the Explorer and Juan de Fuca Plates are remnants of an ancient oceanic plate, the Fallaron Plate which has almost completely disappeared beneath North America. The Fallaron Plate formerly diverged from the Pacific Plate along the Fallaron Ridge, but as the plate has been subducted both it and the ridge have broken up. The remnants of the plate are now the Explorer Plate in the north, then the Juan de Fuca Plate, then the Gorda Plate in the south. This borders onto the Pacific Plate along the Mendocino Fracture Zone, which extends on land as the San Andreas Fault.

North of California the San Andreas Fault becomes the Mendocino Fracture Zone. USGS.

Witness accounts of quakes can help geologists to understand these events and the rock structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) you can report it to the USGS here. 

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Magnitude 5.2 Earthquake in Kern County, California.

The United States Geological Survey recorded a Magnitude 5.2 Earthquake at a depth of about 11.7 km roughly 23 km to the southwest of Lamont in Kern County, California, slightly before 9.10 pm local time on Tuesday 6 August 2024 (slightly before 4.10 am on Wednesday 7 August, GMT). There are no reports of any damage or injuries relating to this quake, but people have reported feeling it across much of southern California.

The approximate location of the 6 August 2024 County Earthquake. USGS.

California is extremely prone to Earthquakes due to the presence of the San Andreas Fault, a tectonic plate margin that effectively bisects the state. The west of California, including Santa Barbara and Los Angeles, is located on the Pacific Plate, and is moving to the northwest. The east of California, including Fresno and Bakersfield is on the North American Plate, and is moving to the southeast. The plates do not move smoothly past one-another, but constantly stick together then break apart as the pressure builds up. This has led to a network of smaller faults that criss-cross the state, so that Earthquakes can effectively occur anywhere.

Tectonic boundaries and faults in California and the surrounding area. USGS.

Witness accounts of Earthquakes can help geologists to understand these events and the underlying structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) then you can report it to the United States Geological Survey here.

See also...

Magnitude 4.1 Earthquake in San Diego County, California.

The United States Geological Survey recorded a Magnitude 4.1 Earthquake at a depth of about 13.3 km roughly 5 km to the west of the Palomar Observatory in San Diego County, California, slightly after 9.45 am local time (slightly before 5.45 pm GMT) on Sunday 30 January 2022. There are no reports of any damage or injuries relating to this quake, but people have reported feeling it across much of southern California, and in parts of northwest Mexico.

 

The approximate location of the 30 January 2022 San Diego County Earthquake. USGS.

California is extremely prone to Earthquakes due to the presence of the San Andreas Fault, a tectonic plate margin that effectively bisects the state. The west of California, including Santa Barbara and Los Angeles, is located on the Pacific Plate, and is moving to the northwest. The east of California, including Fresno and Bakersfield is on the North American Plate, and is moving to the southeast. The plates do not move smoothly past one-another, but constantly stick together then break apart as the pressure builds up. This has led to a network of smaller faults that criss-cross the state, so that Earthquakes can effectively occur anywhere.

 

Tectonic boundaries and faults in California and the surrounding area. USGS.

Witness accounts of Earthquakes can help geologists to understand these events and the underlying structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) then you can report it to the United States Geological Survey here.

See also...

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