The Weekly Volcanic Activity Report: January 31 - February 6, 2024

New activity/unrest was reported for 4 volcanoes from January 31 – February 6, 2024. During the same period, ongoing activity was reported for 15 volcanoes.

New activity/unrest: Kilauea, Hawaiian Islands (USA) | Lewotobi, Flores Island | Mayon, Luzon (Philippines) | Poas, Costa Rica.

New activity/unrest

Kilauea, Hawaiian Islands (USA)

19.421°N, 155.287°W; summit elev. 1222 m

HVO reported that seismicity at Kilauea increased on 27 January and during 27-30 January the locations of the earthquakes became more widespread. Inflation at the summit was ongoing and remained at a high level. Sulfur dioxide gas emission rates were low. Seismicity intensified in the late hours of 30 January, just before midnight. By 0300 on 31 January, the network had recorded 25-30 earthquakes. The earthquakes were located at depths of 1.5-3 km in clusters that had migrated between the area just S of Halema`uma`u Crater and the region SW of the outer caldera boundary. The rate of inflation increased at around 0400. The seismic and deformation data suggested that magma was rising towards the surface, and as a result HVO raised the Volcano Alert Level to Watch (the second highest level on a four-level scale) and the Aviation Color Code to Orange (the second highest level on a four-color scale) at 0441. They noted that the patterns of earthquake activity and ground deformation were concentrated S of the caldera, so new eruptive activity could occur in or near Halema`uma`u Crater or the region S of the caldera.

Seismicity continued to intensify. During 0300-1755 on 31 January, over 500 earthquakes had been located, making a total of more 1,400 earthquakes recorded since 0900 on 27 January. The earthquakes occurred at a rate of 25-40 per hour. The events were located along the Koa’e fault system, SW of the summit. The magnitudes ranged from less than 1 to as high as 3.4; several of the earthquakes were large enough to be felt by HVO staff in the field and neighboring communities. The larger earthquakes triggered rockfalls in Halema`uma`u. About 20 microradians of inflation were detected by deformation instruments.

Seismicity decreased by the morning of 1 February, with 25-30 earthquakes per hour, and throughout the day the rate dropped further to 15-20 earthquakes per hour. The events continued to be located at depths of 1-4 km with epicenters in the vicinity of Pu’ukoa’e, 8-11 km SW of the caldera. Seismic and deformation data suggested that magma continued to move along the fault system. Models suggested that as much as 30 million cubic meters of magma had accumulated in the region SW of the caldera. Instruments detected almost 40 microradians of inflation by the morning on 1 February, but by 2 February the deformation data indicated deflation. Earthquake and ground deformation rates decreased significantly during 2-3 February, suggesting that the intrusion of magma had slowed or stopped and that the likelihood of an eruption had decreased. At 0810 on 3 February the Volcano Alert Level was lowered to Advisory, and the Aviation Color Code was lowered to Yellow.

Geological summary: Kilauea overlaps the E flank of the massive Mauna Loa shield volcano in the island of Hawaii. Eruptions are prominent in Polynesian legends; written documentation since 1820 records frequent summit and flank lava flow eruptions interspersed with periods of long-term lava lake activity at Halemaumau crater in the summit caldera until 1924. The 3 x 5 km caldera was formed in several stages about 1,500 years ago and during the 18th century; eruptions have also originated from the lengthy East and Southwest rift zones, which extend to the ocean in both directions. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1,100 years old; 70% of the surface is younger than 600 years. The long-term eruption from the East rift zone between 1983 and 2018 produced lava flows covering more than 100 km2, destroyed hundreds of houses, and added new coastline.

Lewotobi, Flores Island

8.542°S, 122.775°E; summit elev. 1703 m

PVMBG reported that the eruption at Lewotobi’s Laki-laki volcano was ongoing during 31 January-6 February. Incandescence at the summit and from the lava flow on the NE flank was visible in webcam images during the week. On 31 January dense white-and-gray ash plumes rose as high as 700 m above the summit and drifted N and NE. At 0825 on 2 February a white-and-gray ash plume rose 700 m and drifted N and a pyroclastic flow descended the N flank as far as 500 m. An eruptive event was recorded at 1248 but it was not observed. At 1429 a dense white-and-gray ash plume rose as high as 1.5 km and drifted N. White steam-and-gas plumes were visible on the other days rising to 500 m above the summit and drifting N, NE, and S; no emissions were observed on 4 February. The Alert Level remained at 3 (the second highest level on a scale of 1-4) and the public was warned to stay outside of the exclusion zone, defined as a 4-km radius around Laki-laki crater, 5 km to the NNE, and 6 km on the NE flanks.

Geological summary: The Lewotobi “husband and wife” twin volcano (also known as Lewetobi) in eastern Flores Island is composed of the Lewotobi Lakilaki and Lewotobi Perempuan stratovolcanoes. Their summits are less than 2 km apart along a NW-SE line. The conical Lakilaki has been frequently active during the 19th and 20th centuries, while the taller and broader Perempuan has erupted only twice in historical time. Small lava domes have grown during the 20th century in both of the crescentic summit craters, which are open to the north. A prominent flank cone, Iliwokar, occurs on the E flank of Perampuan.

Mayon, Luzon (Philippines)

13.257°N, 123.685°E; summit elev. 2462 m

PHIVOLCS reported that unrest continued at Mayon during 31 January-6 February. Crater incandescence was visible daily. The seismic network recorded a few volcanic earthquakes and rockfall signals during the week. A phreatic explosion was recorded by the seismic network at 1647 on 4 February and lasted for two minutes and 49 seconds. The explosion produced an ash-and-steam plume that rose 1.2 km above the summit and drifted SW, ejected blocks onto the flanks, and generated pyroclastic density currents that descended the flanks. Booming noises were reported by residents. The Alert Level remained at 2 (on a 0-5 scale). Residents were reminded to stay away from the 6-km-radius Permanent Danger Zone (PDZ) and pilots were advised to avoid flying close to the summit.

Geological summary: Symmetrical Mayon, which rises above the Albay Gulf NW of Legazpi City, is the most active volcano of the Philippines. The steep upper slopes are capped by a small summit crater. Recorded eruptions since 1616 CE range from Strombolian to basaltic Plinian, with cyclical activity beginning with basaltic eruptions, followed by longer term andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often damaged populated lowland areas. A violent eruption in 1814 killed more than 1,200 people and devastated several towns.

Poas, Costa Rica

10.2°N, 84.233°W; summit elev. 2697 m

OVSICORI-UNA reported that small, frequent phreatic eruptions at Poás continued during 30 January-6 February. Data from the monitoring network indicated that around 600 events per day were occurring, though most of the events did not eject material more than 50 m high, and only a few ejected material more than 100 m. At 0712 on 4 February a phreatic eruption produced a plume of steam, sediments, and water that rose 200 m. The report noted that small eruptive events were occurring at a rate of 20-25 events per hour before the 0712 event, ceased afterwards, and then resumed to a rate of about 20 events per hour. On 6 February incandescence at the vent was visible in webcam images and was attributed to the combustion of native sulfur. This phenomenon was last visible in 2019.

Geological summary: The broad vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the complex stratovolcano extends to the lower N flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, last erupted about 7,500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world’s most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since an eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.

Ongoing activity

Ambae, Vanuatu

15.389°S, 167.835°E; summit elev. 1496 m

On 31 January the Vanuatu Meteorology and Geohazards Department (VMGD) reported that steam-and-gas emissions at Ambae were ongoing based on data from monitoring systems. The Alert Level remained at 2 (on a scale of 0-5), and the public was warned to stay outside of the Danger Zone, defined as a 2-km radius around the active vents in Lake Voui, and away from drainages during heavy rains.

Geological summary: The island of Ambae, also known as Aoba, is a massive 2,500 km3 basaltic shield that is the most voluminous volcano of the New Hebrides archipelago. A pronounced NE-SW-trending rift zone dotted with scoria cones gives the 16 x 38 km island an elongated form. A broad pyroclastic cone containing three crater lakes (Manaro Ngoru, Voui, and Manaro Lakua) is located at the summit within the youngest of at least two nested calderas, the largest of which is 6 km in diameter. That large central edifice is also called Manaro Voui or Lombenben volcano. Post-caldera explosive eruptions formed the summit craters about 360 years ago. A tuff cone was constructed within Lake Voui (or Vui) about 60 years later. The latest known flank eruption, about 300 years ago, destroyed the population of the Nduindui area near the western coast.

Ambrym, Vanuatu

16.25°S, 168.12°E; summit elev. 1334 m

The Vanuatu Meteorology and Geo-Hazards Department (VMGD) reported that lava effusion in Ambrym began on 13 January and lasted for four days, producing a lava flow in Benbow Crater. Since then, steam emissions were ongoing and observed through 31 January. The Alert Level remained at 2 (on a scale of 0-5). VMGD warned the public to stay outside of Permanent Danger Zone A, defined as a 1-km radius around Benbow Crater and a 2-km radius around Marum Crater, and to stay 500 m away from the ground cracks created by the December 2018 eruption.

Geological summary: Ambrym, a large basaltic volcano with a 12-km-wide caldera, is one of the most active volcanoes of the New Hebrides Arc. A thick, almost exclusively pyroclastic sequence, initially dacitic then basaltic, overlies lava flows of a pre-caldera shield volcano. The caldera was formed during a major Plinian eruption with dacitic pyroclastic flows about 1,900 years ago. Post-caldera eruptions, primarily from Marum and Benbow cones, have partially filled the caldera floor and produced lava flows that ponded on the floor or overflowed through gaps in the caldera rim. Post-caldera eruptions have also formed a series of scoria cones and maars along a fissure system oriented ENE-WSW. Eruptions have apparently occurred almost yearly during historical time from cones within the caldera or from flank vents. However, from 1850 to 1950, reporting was mostly limited to extra-caldera eruptions that would have affected local populations.

Awu, Sangihe Islands

3.689°N, 125.447°E; summit elev. 1318 m

In a press release for Awu, PVMBG reported that both the number and intensity of earthquake events increased during 29-31 January; the signals possibly indicated the movement of magma to shallower depths. Inflation had been recorded since June 2023 and was ongoing. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to stay at least 3 km away from the summit crater.

Geological summary: The massive Gunung Awu stratovolcano occupies the northern end of Great Sangihe Island, the largest of the Sangihe arc. Deep valleys that form passageways for lahars dissect the flanks of the volcano, which was constructed within a 4.5-km-wide caldera. Powerful explosive eruptions in 1711, 1812, 1856, 1892, and 1966 produced devastating pyroclastic flows and lahars that caused more than 8000 cumulative fatalities. Awu contained a summit crater lake that was 1 km wide and 172 m deep in 1922, but was largely ejected during the 1966 eruption.

Ebeko, Paramushir Island (Russia)

50.686°N, 156.014°E; summit elev. 1103 m

KVERT reported that moderate explosive activity was ongoing at Ebeko during 25 January-1 February. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E), explosions on 29 January and 1 February generated ash plumes that rose as high as 2 km (6,600 ft) a.s.l and drifted SE. The Aviation Color Code remained at Orange (the third level on a four-color scale). Dates are UTC; specific events are in local time where noted.

Geological summary: The flat-topped summit of the central cone of Ebeko volcano, one of the most active in the Kuril Islands, occupies the northern end of Paramushir Island. Three summit craters located along a SSW-NNE line form Ebeko volcano proper, at the northern end of a complex of five volcanic cones. Blocky lava flows extend west from Ebeko and SE from the neighboring Nezametnyi cone. The eastern part of the southern crater contains strong solfataras and a large boiling spring. The central crater is filled by a lake about 20 m deep whose shores are lined with steaming solfataras; the northern crater lies across a narrow, low barrier from the central crater and contains a small, cold crescentic lake. Historical activity, recorded since the late-18th century, has been restricted to small-to-moderate explosive eruptions from the summit craters. Intense fumarolic activity occurs in the summit craters, on the outer flanks of the cone, and in lateral explosion craters.

El Misti, Peru

16.294°S, 71.409°W; summit elev. 5822 m

Instituto Geofísico del Perú (IGP) reported that a lahar descended the NW flank of El Misti at 1640 on 5 February, impacting the Matagente drainage.

Geological summary: El Misti is a symmetrical andesitic stratovolcano with nested summit craters that towers above the city of Arequipa, Peru. The modern symmetrical cone, constructed within a small 1.5 x 2 km wide summit caldera that formed between about 13,700 and 11,300 years ago, caps older Pleistocene volcanoes that underwent caldera collapse about 50,000 years ago. A large scoria cone has grown with the 830-m-wide outer summit crater. At least 20 tephra-fall deposits and numerous pyroclastic-flow deposits have been documented during the past 50,000 years, including a pyroclastic flow that traveled 12 km to the south about 2000 years ago. The most recent activity has been dominantly pyroclastic, and strong winds have formed a parabolic dune field of volcanic ash extending up to 20 km downwind. An eruption in the 15th century affected nearby Inca inhabitants. Some reports of historical eruptions may represent increased fumarolic activity.

Great Sitkin, Andreanof Islands (USA)

52.076°N, 176.13°W; summit elev. 1740 m

AVO reported that slow lava effusion continued at Great Sitkin during 31 January-6 February with growth concentrated at the center of the flow in the summit crater. A few small volcanic earthquakes were recorded by the seismic network each day. Weather clouds obscured satellite and webcam views during most of the week. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Geological summary: The Great Sitkin volcano forms much of the northern side of Great Sitkin Island. A younger parasitic volcano capped by a small, 0.8 x 1.2 km ice-filled summit caldera was constructed within a large late-Pleistocene or early Holocene scarp formed by massive edifice failure that truncated an ancestral volcano and produced a submarine debris avalanche. Deposits from this and an older debris avalanche from a source to the south cover a broad area of the ocean floor north of the volcano. The summit lies along the eastern rim of the younger collapse scarp. Deposits from an earlier caldera-forming eruption of unknown age cover the flanks of the island to a depth up to 6 m. The small younger caldera was partially filled by lava domes emplaced in 1945 and 1974, and five small older flank lava domes, two of which lie on the coastline, were constructed along northwest- and NNW-trending lines. Hot springs, mud pots, and fumaroles occur near the head of Big Fox Creek, south of the volcano. Historical eruptions have been recorded since the late-19th century.

Ibu, Halmahera

1.488°N, 127.63°E; summit elev. 1325 m

PVMBG reported that Ibu continued to erupt during 17-23 January. White-and-gray ash emissions rose 200-1,500 m above the summit and drifted in multiple directions. An eruptive event at 2200 on 2 February produced a white, gray, and black ash plume that rose as high as 2 km above the summit and drifted mainly SW. Booming noises were heard at the observation post. According to a news article, incandescent material was ejected 600 m above the summit and as far as 1 km to the N, NW, W, and S. The Alert Level remained at 2 (the second highest level on a four-level scale), with the public advised to stay outside of the 2 km hazard zone and 3.5 km away from the N area of the active crater.

Geological summary: The truncated summit of Gunung Ibu stratovolcano along the NW coast of Halmahera Island has large nested summit craters. The inner crater, 1 km wide and 400 m deep, has contained several small crater lakes. The 1.2-km-wide outer crater is breached on the N, creating a steep-walled valley. A large cone grew ENE of the summit, and a smaller one to the WSW has fed a lava flow down the W flank. A group of maars is located below the N and W flanks. The first observed and recorded eruption was a small explosion from the summit crater in 1911. Eruptive activity began again in December 1998, producing a lava dome that eventually covered much of the floor of the inner summit crater along with ongoing explosive ash emissions.

Lewotolok, Lembata Island

8.274°S, 123.508°E; summit elev. 1431 m

PVMBG reported that the eruption at Lewotolok continued during 31 January-6 February. White gas-and-steam plumes rose as high as 200 m above the summit and drifted NE, E, and SE on most days. Ejected incandescent material fell around the crater area on 2 February. White-and-gray plumes rose 50-100 m above the summit and drifted E on 5 February. The Alert Level remained at 2 (on a scale of 1-4) and the public was warned to stay at least 2 km away from the summit crater.

Geological summary: The Lewotolok (or Lewotolo) stratovolcano occupies the eastern end of an elongated peninsula extending north into the Flores Sea, connected to Lembata (formerly Lomblen) Island by a narrow isthmus. It is symmetrical when viewed from the north and east. A small cone with a 130-m-wide crater constructed at the SE side of a larger crater forms the volcano’s high point. Many lava flows have reached the coastline. Eruptions recorded since 1660 have consisted of explosive activity from the summit crater.

Marapi, Central Sumatra

0.38°S, 100.474°E; summit elev. 2885 m

PVMBG reported that eruptive activity at Marapi (on Sumatra) was ongoing during 31 January-6 February. White gas-and-steam plumes rose as high as 400 m above the summit and drifted in multiple directions during 31 January-4 February. According to the Darwin VAAC an ash plume rose 400 m above the crater at 0430 on 3 February, though weather conditions prevented identification in satellite data. PVMBG noted that white-and-gray ash plumes rose 100-500 m above the summit and drifted S, SW, and W on 5 February. According to a news source, residents reported vibrations and noises from the volcano from an eruptive event at 1516 on 5 February. The Darwin VAAC reported that at 1528 and 1702 on 6 February ash plumes were identified in satellite images rising as high as 800 m above the summit and drifting S. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 4.5 km away from the active crater.

Geological summary: Gunung Marapi, not to be confused with the better-known Merapi volcano on Java, is Sumatra’s most active volcano. This massive complex stratovolcano rises 2,000 m above the Bukittinggi Plain in the Padang Highlands. A broad summit contains multiple partially overlapping summit craters constructed within the small 1.4-km-wide Bancah caldera. The summit craters are located along an ENE-WSW line, with volcanism migrating to the west. More than 50 eruptions, typically consisting of small-to-moderate explosive activity, have been recorded since the end of the 18th century; no lava flows outside the summit craters have been reported in historical time.

Merapi, Central Java

7.54°S, 110.446°E; summit elev. 2910 m

BPPTKG reported that the eruption at Merapi (on Java) continued during 26 January-1 February. Seismicity remained at high levels. The SW lava dome produced 143 lava avalanches, triple in number compared to the previous week, that descended the S and SW flanks: three traveled S as far as 1 km down the upper part of the Boyong drainage and 140 traveled SW as far as 1.7 km down the upper part of the Bebeng drainage. A total of 10 pyroclastic flows descended the Bebeng drainage, traveling as far as 2.4 km. Morphological changes to the SW lava dome identified in webcam images were due to continuing effusion and collapses of material. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 3-7 km away from the summit, based on location.

Geological summary: Merapi, one of Indonesia’s most active volcanoes, lies in one of the world’s most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2,000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequent growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities.

Semeru, Eastern Java

8.108°S, 112.922°E; summit elev. 3657 m

PVMBG reported that eruptive activity continued at Semeru during 31 January-6 February. Daily gray-and-white ash plumes rose 500-1,300 m above the summit and drifted W, N, and NE. The Alert Level remained at 3 (the third highest level on a scale of 1-4). The public was warned to stay at least 5 km away from the summit in all directions, 13 km from the summit to the SE, 500 m from the banks of the Kobokan drainage as far as 17 km from the summit, and to avoid other drainages including the Bang, Kembar, and Sat, due to lahar, avalanche, and pyroclastic flow hazards.

Geological summary: Semeru, the highest volcano on Java, and one of its most active, lies at the southern end of a volcanic massif extending north to the Tengger caldera. The steep-sided volcano, also referred to as Mahameru (Great Mountain), rises above coastal plains to the south. Gunung Semeru was constructed south of the overlapping Ajek-ajek and Jambangan calderas. A line of lake-filled maars was constructed along a N-S trend cutting through the summit, and cinder cones and lava domes occupy the eastern and NE flanks. Summit topography is complicated by the shifting of craters from NW to SE. Frequent 19th and 20th century eruptions were dominated by small-to-moderate explosions from the summit crater, with occasional lava flows and larger explosive eruptions accompanied by pyroclastic flows that have reached the lower flanks of the volcano.

Sheveluch, Central Kamchatka (Russia)

56.653°N, 161.36°E; summit elev. 3283 m

KVERT reported that the eruption at Sheveluch continued during 25 January-1 February with a daily thermal anomaly identified in satellite images. The Aviation Color Code remained at Orange (the third level on a four-color scale). Dates are based on UTC times; specific events are in local time where noted.

Geological summary: The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1,300 km3 andesitic volcano is one of Kamchatka’s largest and most active volcanic structures, with at least 60 large eruptions during the Holocene. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes occur on its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large open caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Stromboli, Aeolian Islands (Italy)

38.789°N, 15.213°E; summit elev. 924 m

INGV reported that eruptive activity continued at Stromboli during 29 January-4 February. Webcam images showed Strombolian activity at three vents in Area N (one at N1 and two at N2), within the upper part of the Sciara del Fuoco, and from two vents at S2 in Area C-S (South-Central Crater) in the crater terrace. Weather conditions sometimes prevented webcam views. Low-intensity explosions occurred at a rate of 2-5 per hour at Area N2 and ejected mainly coarse material (bombs and lapilli) as high as 80 m above the vents. Variable-intensity explosions in sector S2 (Area C-S) averaged 5-9 per hour from the vents, ejecting a mix of coarse material higher than 150 m. The Dipartimento della Protezione Civile maintained the Alert Level at Yellow (the second highest level on a four-level scale).

Geological summary: Spectacular incandescent nighttime explosions at Stromboli have long attracted visitors to the “Lighthouse of the Mediterranean” in the NE Aeolian Islands. This volcano has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period took place between about 13,000 and 5,000 years ago. The active summit vents are located at the head of the Sciara del Fuoco, a prominent scarp that formed about 5,000 years ago due to a series of slope failures which extends to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild Strombolian explosions, sometimes accompanied by lava flows, have been recorded for more than a millennium.

Suwanosejima, Ryukyu Islands (Japan)

29.638°N, 129.714°E; summit elev. 796 m

JMA reported that the eruption at Suwanosejima’s Ontake Crater continued during 29 January-5 February. Crater incandescence was observed in webcam images nightly and rumbling was occasionally heard in Toshima village (3.5 km SSW). A total of three explosions were recorded during the week, ejecting large blocks as far as 300 m from the vent. The first explosion, at 1135 on 29 January, produced an ash plume that rose 1 km above the crater rim and drifted SE. The second explosion was recorded at 0950 on 31 January, though details about emissions were unknown. The third explosion, at 2223 on 31 January, generated an ash plume that rose 500 m and drifted E. The Alert Level remained at 2 (on a 5-level scale) and the public was warned to stay at least 1 km away from the crater.

Geological summary: The 8-km-long island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two historically active summit craters. The summit is truncated by a large breached crater extending to the sea on the east flank that was formed by edifice collapse. One of Japan’s most frequently active volcanoes, it was in a state of intermittent Strombolian activity from Otake, the NE summit crater, between 1949 and 1996, after which periods of inactivity lengthened. The largest recorded eruption took place in 1813-14, when thick scoria deposits blanketed residential areas, and the SW crater produced two lava flows that reached the western coast. At the end of the eruption the summit of Otake collapsed, forming a large debris avalanche and creating the open Sakuchi caldera, which extends to the eastern coast. The island remained uninhabited for about 70 years after the 1813-1814 eruption. Lava flows reached the eastern coast of the island in 1884. Only about 50 people live on the island.

Yasur, Vanuatu

19.532°S, 169.447°E; summit elev. 361 m

On 31 January the Vanuatu Meteorology and Geohazards Department (VMGD) reported that activity at Yasur continued at a level of “major unrest,” as defined by the Alert Level 2 status (on a scale of 0-5) during the month. Recent satellite observations indicated an increase in steam, gas, and ash emissions from the summit crater. Explosions continued, with some ejecting bombs that landed back in and around the crater. The public was reminded to not enter the restricted area within 600 m around the boundaries of the Permanent Exclusion Zone, defined by Danger Zone A on the hazard map.

Geological summary: Yasur has exhibited essentially continuous Strombolian and Vulcanian activity at least since Captain Cook observed ash eruptions in 1774. This style of activity may have continued for the past 800 years. Located at the SE tip of Tanna Island in Vanuatu, this pyroclastic cone has a nearly circular, 400-m-wide summit crater. The active cone is largely contained within the small Yenkahe caldera, and is the youngest of a group of Holocene volcanic centers constructed over the down-dropped NE flank of the Pleistocene Tukosmeru volcano. The Yenkahe horst is located within the Siwi ring fracture, a 4-km-wide open feature associated with eruption of the andesitic Siwi pyroclastic sequence. Active tectonism along the Yenkahe horst accompanying eruptions has raised Port Resolution harbor more than 20 m during the past century.

References:

¹ Smithsonian Institution / US Geological Survey – Weekly Volcanic Activity Report – January 31 – February 6, 2024 – Managing Editor: Sally Sennert.

Featured image credit: TW

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