Category Archives: Asia

Asia, Japan

Mount Fuji (Fujisan)

Leave a comment

Taking a break from eruptions and seismic activity in Iceland, and disasters, in this article, we are taking a look at subduction zone volcanism, with Mount Fuji as our example.

Mount Fuji is stratovolcano located 100km south west of Tokyo in Honshu, Japan, in the Fuji-Hakone national park. The main crater is 780 m diameter at the top, 100 -130 m diameter at its base, and 240 m deep. The highest point, the Kengamine Peak, 3776 m, was built during the Kengamine eruption c.2,300 years ago, the last known summit eruption.  The most recent eruption was the 1707 Hoei eruption.

Fujisan is one of Japan’s three holy mountains, the others being Mount Tate and Mount Haku. It was viewed as a living god and a bridge between Earth and Heaven by ancient peoples.  In the Shinto religion, Konohanasakuya-hime is a goddess representing fire and volcanoes.  There are shrines to her at the summit and foot of the volcano to calm volcanic fire. Buddists climb the volcano for spiritual meditation and enlightenment. 

Mount Fuji is a very popular tourist destination due to its natural beauty and climbing trails.  It was declared a world cultural site in 2013.

Fig 1: Photo by Ichio Moriya (Kanazawa University) of Fujisan with the Tokyo-Osaka highway. Hoeisan, the smaller cone on the SE flank (to the right), is a remant of Kofuji (Old Fuji). Source: Global Volcanism Program | Volcano Photo Collection — Image GVP-08934. This image is made available under the Creative Commons BY-NC 4.0 license terms.

Tokyo, the capital and economic centre of Japan and a major international finance centre, has a population of 14 million; the Greater Tokyo area has one of 33 million.  According to Wikipedia, in 2022, Tokyo’s gross regional product was US$887.9 billion, accounting for 21.2% of the country’s total economic output.  Of the total output, wholesale and retail was 21.5,  real estate (13.5%), professional, scientific and technical (12.2%), information and communications (11.7%), finance and insurance (7.6%), manufacturing (7.0%), and healthcare (6.7%). Agriculture, forestry and fishery, and mining combined accounted for less than 0.1% of the economic output. Lying near the boundary of three tectonic plates (the Okhotsk, Amur Philippine Sea Plates) and also on the Kantō Plain, Tokyo is at risk from earthquake and volcanic activity, and also floods, especially when typhoon rains swell the many rivers on the Plain.

Fig 2: Screenshot from Google Earth (https://earth.google.com/) showing built up areas near Mount Fuji.  Mount Fuji is the snow capped volcano in the left of the image.  Eagle eyed readers will spot that Mount Fuji is not the only volcano in the image.

While Tokyo is the largest conurbation near Mount Fuji, there are several heavily built up areas nearby, including the cities of Yokohama, Fujinomiya, Gotemba, Fujiyoshida, Fuji City, Fujikawaguchiko, Numazu, Kofu, Hakone and Odawara. The Smithsonian Institute National Museum of Natural History Global Volcanism Program (GVP) notes that a population of nearly 1 million live within 30km of the summit and just over 25 million live within 100 km.  At the time of writing, Google’s AI gives a figure of between 30 – 37 million for people living within 100km of the summit (multiple searches gave different answers but all were in this ball park).

Hazards

The main hazards posed by Mount Fuji, itself, which may cause fatalities and injuries, damage health, livestock, crops, buildings, infrastructure and communications are:

  • Eruptive products: ash, cinders, lapilli and lava. 
  • Lahars and flooding from rains, which may include typhoon rains.
  • Debris avalanche flows caused by volcanic or seismic activity.
  • Differing eruptive styles complicating predictions

Other local geological hazards include large destructive earthquakes as the region is tectonically very active. 

It is worth noting that because Mount Fuji is close to densely populated areas, including the capital the site of government and a large international financial market), the impact of any large future eruption could be not only be nationally but also globally significant.

The volcano is closely monitored by several agencies coordinated by the Japan Meteorological Agency.

Evolution

Fig 3: Image by TTL2698 of the geological cross-section of Fuji. Key: N2 (yellow) = Tertiary sedimentary rocks; αN2  (dark pink)  = Tertiary volcanic rocks; αQ1  (orange) = Komitake volcano; α-δQ1 (dark orange) = Ashitaka volcano; βQ2 (green) = Older Fuji volcano; αβQ2 (light green) = Younger Fuji volcano. Source: Geological cross-section of Fuji.png – Wikimedia Commons, published under CC BY-SA 3.0.

Mount Fuji last erupted in 1707-1708 with a large explosive eruption of VEI 5, preceded 49 days earlier by a the magnitude 8.7 Hoei earthquake on the Nankai Trough, a 900 km trough off the southern coast of Honshu where the Philippine Sea Plate subducts under the Amur and Okinawa Plates.  The eruption was Plinian, occurring on the SE flank of the volcano. Erupted products were mostly pyroclastic, starting with dacite pumice, followed by andesitic scoria, and, finally, basaltic scoria.  Ash fall several centimetres thick reached Edo (now Tokyo).  The ashfall damaged crops in the region causing widespread starvation.  Rainfall combined with ash deposits caused multiple lahars and flooding.  Most fatalities were caused by flooding, landslides and famine.  It took nearly 100 years for the region to recover.

While the last eruption was explosive, Mount Fuji has produced effusive eruptions in its past.  Studies of lavas show that Mount Fuji overlies older volcanoes.

Sen-komitake is an andesitic core discovered in 2004.  Andesitic activity started here 270,000 years ago ending 160,000 years ago.

Komitake – Fuji is a basaltic layer several hundred thousand years old.  Large basaltic lava flows started here started 700,000 years ago, ending 100,000 years ago, .

Old Fuji formed over Komitake – Fuji between100,000 to 17,000 years ago, the Hoshiyama stage.  Activity in this period is explosive with Plinian or sub-Plinian eruptions, dominated by ash clouds, heavy pyroclastic flows, mudflows, and massive scoria fall. Komitake – Fuji was nearly completely covered. Around 18,000 BC the edifice collapsed with a large debris avalanche flow to the southwest, forming the Tanukiko debris avalanche deposit.  This was followed by another collapse eastwards c. 12,000 BC forming the Umafusegawa debris avalanche deposit.

New Fuji formed over old Fuji during the Fujinomiya stage from 15,000 BC to 6,000 BC. The new edifice was constructed within the Tanukiko avalanche scar.  The eruptive style switched back to large effusive basaltic lava flows, including the Mishima, Obuchi and Saruhashi lava flows.  The Mishima lava flow is estimated to have a volume of 4.3 km3  and the Obuchi 1.1 km3.  The Saruhashi lava flow is the longest, extending more that 40 km from the summit.

From 6,000 BC to 3,600 BC, the Subashiri – a stage, activity declined considerably.  Only Fuji black soil round the volcano remains.

The Subashiri – b stage, from 3,600 BC to 1,700 BC, marked an increase in activity during which the current cone was built from thin basaltic lava flows up to 2,100 BC.  Effusive flank eruptions also occurred during this period.

The Subashi – c stage, 1,700 BC to 300 BC was marked by initial explosive basaltic Plinian or sub-Plinian eruptions from the summit, 1,700 BC to 1,300 BC, flowed by scoria cone forming flank eruptions, 1,300 BC to 1,000 BC,  The Gotemba debris avalanche flow occurred c.900 BC  removing the remains of the eastern flank of the Hoshiyama stage edifice.  Explosive summit basaltic eruptions became dominant again.

The Subashi – d stage runs from 300 BC to present. This stage is marked by frequent basaltic flank eruptions within 13.5 km of the summit. The last summit eruption, the Kengamine eruption, occurred c.2,300 years ago, after which activity has switched to flank eruptions, notably the Yufune 2 eruption 2,000-2,2000 years ago.  Both eruptions produced highly fluid basaltic lavas that generated extensive scoria fallouts. 

 The two most recent largest eruptions are the 864 AD – 866 AD Jogan eruption and also the 1707 Hoei eruption that we have already mentioned.  The Jogan eruption was a VEI 3, occurring on the northwest flank near Nagaoyama, discharging 1.5 km3 of basaltic Aokigahara Lava Flow. The lava flowed into Lake Senoumi, splitting it into two smaller lakes, Lake Saiko and Lake Shōjiko.  Ash and lapilli emitted from the summit, with fallout reaching as far as Edo Bay and Kai Province.  The eruption buried villages, destroyed homes and caused a number of fatalities.

Magmas

Mount Fuji lies on the north end of the Izu-Bonin-Mariana Arc, near the junction with the South Western Japan Arc and North Eastern Japan Arc.  Unlike other arc volcanoes with intermediate and felsic lavas, basaltic lavas dominate.

It is thought that Mount Fuji has two magma reservoirs: the first, a basaltic one, with a depth of c.20 km at the bottom of the granitic middle crust of the Philippine Sea Plate, and the second, a more silicic one with a depth of  8 -9 km.  The lower magma reservoir is deeper than that of other arc volcanoes whose reservoirs tend to be less than 10 km deep.

Analysis of the chemical composition of Mount Fuji’s lavas showed that new activity in the Subashiri period was driven be an injection of basaltic magma 5,600 years ago.  The eruptive style was stable with effusive eruptions until 3,450 years ago when the style changed from effusive to explosive.  The transition from effusive to explosive is thought to be driven by a change in the water content of the parental magmas.

Tectonic Setting

Mount Fuji lies near the triple junction of the Philippine Sea Plate, Amur Plate and Okhotsk Plates. The Philippine Sea Plate subducts under the Amur Plate.  The Pacific Plate also subducts under the region. 

Fig 4: Plates near Mount Fuji.  Image extracted from File:Tectonic plates boundaries detailed-en.svg – Wikimedia Commons, published under CC BY-SA 4.0.  Plate names in black added by the author where the screenshot has excluded them.

Seismic Activity

Our focus here is tectonic activity in the region, not magmatic activity (we do not have access to the data for the latter).  We looked at the area 39°N,133.5°E to 30°N, 147°E from 1st January 2006 to 24th August 2026. 

Our plots show the dominance of the subduction of the Pacific Plate in the area. In the geoscatter plot we can also just about see the triple junction near Mount Fuji delineated in shallow (purple) earthquakes.

What we cannot see clearly in any of our plots is the subduction of the Philippine Sea Plate; however, this is visible in our plot of the area to the west, 39.63°N, 153.14°E to 28.60°N, 124.75°E, where we can see subduction under the Okinawa Plate (Shallow 6.8 magnitude Earthquake South of Kumamoto, Japan, 28th July 2026). This implies that the Philippine Sea Plate may not subduct under the Amur Plate but has a different type of boundary, which may. or may not. contribute to the basaltic magmas of Mount Fuji.

Fig 5: Geoscatter plot by the author of earthquakes between 39°N,133.5°E and 30°N, 147°E from 1st January 2006 to 24th August 2026.  Colour of earthquakes with magnitude less than 6 denotes depth: purple, 0-33km, blue 33-70km, green 70-150km, yellow, 150-300km. orange, 300-500km, red ≥500km. Yellow stars are earthquakes between 6.0 and 7.0 magnitude.  Red stars are earthquakes with magnitude ≥ 7.0. The cyan triangle is the rough location of Mount Fuji.  © Copyright remains with the author, all rights reserved, 2026.
Fig 6: Scatter plot by the author of earthquakes between 39°N,133.5°E and 30°N, 147°E from 1st January 2006 to 24th August 2026.  Colour of earthquakes with magnitude less than 6 denotes depth: purple, 0-33km, blue 33-70km, green 70-150km, yellow, 150-300km. orange, 300-500km, red ≥500km. Yellow stars are earthquakes between 6.0 and 7.0 magnitude.  Red stars are earthquakes with magnitude ≥ 7.0. The cyan triangle is the rough location of Mount Fuji. © Copyright remains with the author, all rights reserved, 2026.

Armchair Volcanologist

© Copyright remains with the author, all rights reserved, 2026.

Sources

USGS for raw earthquake data: Earthquake Hazards Program | U.S. Geological Survey

Yamamoto, T., Nakano, S. & Ishizuka, Y. Temporal variations of magma composition, eruption style and rate at Fuji Volcano, Japan. Earth Planets Space 73, 169 (2021). https://doi.org/10.1186/s40623-021-01505-1

Yosuke Aokia, Kae Tsunematsu , Mitsuhiro Yoshimoto, Recent progress of geophysical and geological studies of Mt. Fuji Volcano, Japan, Earth-Science Reviews

Volume 194, July 2019, Pages 264-282. https://doi.org/10.1016/j.earscirev.2019.05.003

Yamamoto, T., Nakada, S., Extreme Volcanic Risks 2: Mount Fuji, Volcanic Hazards, Risks and Disasters, 2015, Chapter 14, ISBN 978-0-12-396453-3

Wikipedia: Mount Fuji – Wikipedia

Global Volcanism Program, 2026. Fujisan (283030) in [Database] Volcanoes of the World (v. 5.4.0; 7 Aug 2026). Distributed by Smithsonian Institution, compiled by Venzke, E. https://doi.org/10.5479/si.GVP.VOTW5-2026.5.4 . Specific link to Fujisan: Global Volcanism Program | Fujisan

Wikipedia: Tokyo – Wikipedia

Asia, Japan

Shallow 6.8 magnitude Earthquake South of Kumamoto, Japan, 28th July 2026

1 Comment

On 28th July 2026 a 7.1 magnitude (USGS 6.8 magnitude) earthquake struck Uto, south of Kumamoto, Kyushu.  At the time of writing, 34 fatalities had been reported, with 123 injured and 9,000 people displaced.  The earthquake was widely felt, including as far afield as China. In 2016 the area was hit by three large earthquakes: a 6.2 and 6.0, followed by a 7.0 the following day. Our thoughts are with the victims, their families and friends, and everyone else impacted.

Fig 1: Inside Aeon Mall, 警察庁, CC BY 4.0, via Wikimedia Commons

Shinichi Sakai, from the Earthquake Research Institute, University of Tokyo, has said that the earthquake may have been caused by slip on the southern portion of the Hinagu Fault. During the 2016 Kumamoto earthquakes, only the northern extent of the Hinagu Fault slipped. The Hinagu Fault is located in the southern section of  Futagawa-Hinagu fault zone, the Futugawa Fault to the north.  This fault zone lies at the southern end of the Japan Median Tectonic Line, Japan’s longest fault system, which begins near Ibaraki Prefecture on the Pacific coast of Honshu and  runs parallel to Japan’s volcanic arc to Kyūshū.

Fig 2  Shake map  for  2026 6.8  Kumamoto Earthquake  by USGS, Published in the public domain, via Wikimedia Commons.

The Geospatial Information Authority of Japan reported ground deformation: in Yatsushiro, the Sencho geographic reference point was displaced 0.84 m (2 ft 9 in) northeast, and the Izumi station recorded a 0.17 m (6.7 in) movement southward; in Kumamoto, the Jonan station recorded 0.4 m (1 ft 4 in) of displacement to the north.   Surface ruptures along the Hinagu Fault damaged roads, bridges, and buildings. 

Some of the fatalities and injuries were caused by the collapse of the second floor of Aeon Mall Kumamoto, followed by an explosion; a factory chimney, part of the 19th century Yatsushiro-gūshrine and part of bridge collapsed in Yatsushiro; fires were also reported in Yatsushiro.  Damage to rail infrastructure occurred; a freight train derailed near Yatsushiro Station;  there were more than 200 reports of snapped rails and collapsed sound barriers; bent rails were reported at a train depot in Kumamoto and between Matsubashi and Ogawa stations on the Kagoshima Main Line. Landslides occurred on Mount Mayuyama.  48,300 homes lost power in Kumamoto Prefecture; businesses were also impacted. Kumamoto Castle, which was undergoing restoration work following the 2016 Kumamoto earthquakes, was extensively damaged.

Tectonic Setting

The Japanese Archipelago comprises 5 main islands, Hokkaido, Honshu, Shikoku, Kyushu and Okinawa. and c.14,000 smaller islands. Its geology is dominated by the subduction of the Pacific Plate in the north and the subduction of the Philippine Sea Plate in the south.  Japan is seismically very active and home to  c.100 active volcanoes.

Fig 3:  Amur Plate by Alataristarion, CC BY-SA 4.0 , via Wikimedia Commons.  The Okinawa Plate is the small plate between the Philippine Sea Plate and the Yangtze Plate.

Kyushu Island, itself, lies on the rift boundary between the Amur and Okinawa Plate to the west of the subduction of the Philippine Sea Place under these plates.   

The Amur Plate is a small tectonic plate located on the eastern edge of the Eurasian Plate.  It has clearly defined boundaries on the the south by the Qinling suture zone in central China and the Baikal Rift Zone and Stanovoy Mountains on the north. The eastern boundary is with the Okhotsk Plate. The plate is moving anti-clockwise, according to GPS measurements.

The Okinawa Plate is another small continental tectonic plate. To its north is the Amur Plate.  On its eastern margin the Philippine Sea Plate subducts at the Ryuku Trench.  On its western edge there a divergent boundary with the Yangstze Plate.

The Philippine Sea Plate, comprising oceanic lithosphere, lies beneath the Philippine Sea, to the east of the Philippines.  The Philippine Sea plate, the Amur Plate, and the Okhotsk plate meet near Mount Fuji in Japan.

Seismicity

We plotted earthquakes occurring from 1st January 2006 to 30th July 2026 10:00am between 39.63°N, 153.14°E to 28.60°N, 124.75°E.  Our download from USGS contained 17,396 events. The plots clearly show the subduction zones.

Fig 4: Geoscatter plot by the author of earthquakes occurring from 1st January 2006 to 30th July 2026 10:00am between 39.63°N, 153.14°E to 28.60°N, 124.75°E.  For earthquakes of magnitude less than 6.5, colour denotes depth:  purple, 0-33km, blue 33-70km, green 70-150km, yellow, 150-300km. orange, 300-500km, red ≥500km. © remains with the author, all rights reserved, 2026. Yellow stars are earthquakes between 6.5 and 6.8 magnitude.  Orange stars are earthquakes with magnitude ≥ 6.8. © Copyright remains with the author, all rights reserved, 2026.
Fig 5: 3D scatter plot by the author of earthquakes occurring from 1st January 2006 to 30th July 2026 10:00am between 39.63°N, 153.14°E to 28.60°N, 124.75°E.  For earthquakes of magnitude less than 6.5, colour denotes depth:  purple, 0-33km, blue 33-70km, green 70-150km, yellow, 150-300km. orange, 300-500km, red ≥500km. © Copyright remains with the author, all rights reserved, 2026.

Thank you for visiting.

Armchair Volcanologist

© Copyright remains with the author, all rights reserved, 2026.

Sources:

USGS for raw earthquake data: Earthquake Hazards Program | U.S. Geological Survey

Wikipedia: 2026 Kumamoto earthquake – Wikipedia

Asia, Philippines

Philippine Earthquake, Magnitude 7.8 08/06/2026

On 8th June 2026 at 07:37 (local time) a 7.8 magitude earthquake occurred 32 km south west of Maasim in Sarangi Province, off the coast of Mindanao Island, Philippines, with a depth of 33 km.  Tragically, at the time of writing reports suggest that at least 55  people were killed, 38 missing, 1,120 injured, with 390,000 people impacted.  Severe infrastructure damage has impacted rescue and recovery services.  A tsunami, with waves ranging from a few centimetres to 1.4 metres, was recorded.  Our thoughts are with all those affected now and in the coming months.

Fig 1: Location of the 7.8 Philppines earthquake.  Source PhiVolcs: PRIMER ON THE 08 JUNE 2026 MAGNITUDE (MW) 7.8 OFFSHORE SARANGANI EARTHQUAKE | PHIVOLCS

Tectonic Setting

The Philippines  is an archipelago made up of c.7,641 islands.  It lies on the Philippine Mobile Belt, a zone lying above two opposing subduction zones: the Sunda Plate along the western edge at the Manila, Negros and Cotabato Trenches ; and, the Philippine Sea Plate on the eastern edge along the Philippine Trench and the East Luzon Trough. The Philippine Mobile Belt, itself, is the result of oblique collision between the westward-moving Philippine Sea Plate and the eastern margin of the Sunda Plate. It is rapidly deforming, made up of fragments of continental and oceanic crust.

Fig 2:  Map of Philippine Faults by Gubernatoria, published under CC BY 2.5 AU <https://creativecommons.org/licenses/by/2.5/au/deed.en&gt;, via Wikimedia Commons

The 7.8 earthquake was reverse thrust and attributed to movement at the Cotabato Trench.

The archipelago has three main geological features:

  • The 1,200-kilometer-long Philippine Fault Zone; a  strike-slip fault system which accommodates much of the shearing force caused by the colliding plates.  It is seismically active producing large earthquakes, including the destructive M7.6 Luzon earthquake of 1990.
  • Volcanism from the subduction. The Philippines is home to numerous active volcanoes, e.g., Taal, Mayon and Mount Pinatubo
  • A complex structure containing a mixture of ancient metamorphic rocks (dating back to the Jurassic and Cretaceous periods), early volcanic arcs, and microcontinental blocks.
  • The 7.8 earthquake is attributed to movement at the Cotabato Trench.

All in all, an interesting are to study seismicity.

Our Plots

We looked at the area 4.4150°N, 116.16°E  to  21.1218°N, 137.90°E for the period 1st January 2016 to 11th June 2026 (07:33 am).  Our raw data was downloaded publicly available earthquake data from USGS, a total of 7,357 earthquakes with a  minimum magnitude of 3.7 and maximum depth of c.668 km. 

Fig 3: Geoscatter plot of earthquakes occurring between 4.4150°N, 116.16°E  to  21.1218°N, 137.90°E for the period 1st January 2016 to 11th June 2026 (07:33 am).  Earthquakes with magnitude ≥ 7.0 are shown as yellow stars; the magnitude 7.8 earthquake is shown as an orange star.  Smaller earthquakes are coloured by depth as per the legend; their transparency has been increased so we can see the land. © copyright remains with the author; all rights reserved, 2026.

In our Geoscatter plot, we can clearly see the seismicity on the Manila Trench, west of Luzon, the Philippine Trench east of the Philippines, the Philippine Fault Zone to the west of the Philippine Trench and other trenches. Activity along the Philippine Trench dominates the plot.  Most of the earthquakes with magnitude greater than 7.0 are associated with subduction at the Philippine Trench.

We can also see some deeper activity  in the southern part of the plot.  We think that this is related to the fully subducted Molucca Sea Plate which lies to the south of the Philippine Mobile Belt.  The Molucca Sea Plate lies between the southeastward subducting Sangihe Plate and the northwestward subducting Halmahera Plate; the collision zone is thought to be arc to arc collision rather than the more usual arc to continent collision.    This shows better in our scatter plot below.

Fig  4:  Video of 3D scatter plot of of earthquakes occurring between 4.4150°N, 116.16°E  to  21.1218°N, 137.90°E for the period 1st January 2016 to 11th June 2026 (07:33 am).  Earthquakes with magnitude ≥ 7.0 are shown as yellow stars; the magnitude 7.8 earthquake is shown as a black star.  Smaller earthquakes are coloured by depth as per the legend. © copyright remains with the author; all rights reserved, 2026.

In the video we can see that most of the magnitude seven and over earthquakes occur in the region between 0 to 100 km in the southern part of the region and a few are occurring at a depth of over 600 km.  The former are mostly associated with the Philippine Fault Zone and the Philippine Trench.

We hope you find the earthquake plots useful. 

Once again, our thoughts are with all those impacted by the earthquake.

Armchair Volcanologist

© copyright remains with the author; all rights reserved, 2026.

Sources:

USGS:  https://earthquake.usgs.gov/earthquakes

China Daily Asia: Philippine quake death toll reaches 55, search on for 38 missing

PhiVolcs: PRIMER ON THE 08 JUNE 2026 MAGNITUDE (MW) 7.8 OFFSHORE SARANGANI EARTHQUAKE | PHIVOLCS