The Weekly Volcanic Activity Report: October 4 – 10, 2023

the weekly volcanic activity report

New activity/unrest was reported for 4 volcanoes from October 4 to 10, 2023. During the same period, ongoing activity was reported for 17 volcanoes.

New activity/unrest: Inielika, Flores Island | Klyuchevskoy, Central Kamchatka (Russia) | Ruby, Mariana Islands (USA) | Villarrica, Central Chile.

Ongoing activity: Aira, Kyushu (Japan) | Ebeko, Paramushir Island (Russia) | Great Sitkin, Andreanof Islands (USA) | Ibu, Halmahera | Katmai, Alaska | Lascar, Northern Chile | Lewotolok, Lembata Island | Mayon, Luzon (Philippines) | Merapi, Central Java | Nishinoshima, Izu Islands | Popocatepetl, Mexico | Semeru, Eastern Java | Sheveluch, Central Kamchatka (Russia) | Shishaldin, Fox Islands (USA) | Suwanosejima, Ryukyu Islands (Japan) | Ubinas, Peru | Whakaari/White Island, North Island (New Zealand).

New activity/unrest

Inielika, Flores Island

8.73°S, 120.98°E | Summit elev. 1559 m

PVMBG reported that seismicity at Inielika generally consisted of low levels of low-frequency earthquakes and 0-1 daily deep volcanic earthquakes. Seismicity began to increase on 29 September and remained elevated at least through 4 October. The daily number of deep volcanic earthquakes increased to an average of 9, though notably a total of 17 were recorded on 1 October and 18 were recorded on 3 October. The temperatures and gas concentrations at four hot spring locations had significantly decreased compared to July measurements. The Alert Level was raised to 2 (on a scale of 1-4) at 1000 on 4 October due to increased potential for a phreatic eruption; the public was warned to stay at least 1 km away from the summit crater and to stay away from solfatara zones.

Geological summary: Inielika is a broad, low volcano in central Flores Island that was constructed within the Lobobutu caldera. The complex summit contains ten craters, some of which are lake filled, in a 5 km2 area north of the city of Bajawa. The largest of these, Wolo Runu and Wolo Lega North, are 750 m wide. A phreatic explosion in 1905 formed a new crater, and was the volcano’s only eruption during the 20th century. Another eruption took place about a century later, in 2001. A chain of Pleistocene cinder cones, the Bajawa cinder cone complex, extends southward to Inierie.

Klyuchevskoy, Central Kamchatka (Russia)

56.056°N, 160.642°E | Summit elev. 4754 m

KVERT reported that the Strombolian eruption at Klyuchevskoy continued 28 September-11 October. Lava fountaining fed flows that alternately advanced down the Apakhonchichsky and Kozyrevsky drainages on the S and SE flanks. A daily bright thermal anomaly was identified in satellite images; the anomaly was larger during 8-9 October. On 11 October activity increased and gas-and-steam plumes containing a small amount of ash drifted 65 km NE. The Aviation Color Code was raised to Orange (the third level on a four-color scale). Dates and times are in UTC; specific events are in local time where noted.

Geological summary: Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka’s highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

Ruby, Mariana Islands (USA)

15.605°N, 145.572°E | Summit elev. 174 m

The US Geological Survey lowered both the Aviation Color Code and Volcano Alert Level for Ruby to Unassigned on 6 October, noting that eruptive activity was last detected during 14-15 September. The level of Unassigned reflected the lack of nearby monitoring instruments that could detect lower-level events.

Geological summary: Ruby is a basaltic submarine volcano that rises to within about 200 m of the ocean surface near the southern end of the Mariana arc NW of Saipan. An eruption was detected in 1966 by sonar signals (Norris and Johnson, 1969). Submarine explosions were heard in 1995, accompanied by a fish kill, sulfurous odors, bubbling water, and the detection of volcanic tremor.

Villarrica, Central Chile

39.42°S, 71.93°W | Summit elev. 2847 m

On 6 October SERNAGEOMIN lowered the Volcanic Alert Level for Villarrica to Yellow (the second level on a four-level scale), noting that activity had returned to moderate and more stable levels during the previous few days. The frequency and intensity of emissions had declined; gas emissions rose to low heights and sometimes contained small amounts of tephra. Nighttime crater incandescence was observed, and Strombolian explosions ejected material onto the upper flanks. The public was warned to stay at least 2 km away from the crater. SENAPRED maintained the Alert Level at Yellow (the middle level on a three-color scale) for the communities of Villarrica, Pucón (16 km N), Curarrehue, and Panguipulli.

Geological summary: The glacier-covered Villarrica stratovolcano, in the northern Lakes District of central Chile, is ~15 km south of the city of Pucon. A 2-km-wide caldera that formed about 3,500 years ago is located at the base of the presently active, dominantly basaltic to basaltic-andesite cone at the NW margin of a 6-km-wide Pleistocene caldera. More than 30 scoria cones and fissure vents are present on the flanks. Plinian eruptions and pyroclastic flows that have extended up to 20 km from the volcano were produced during the Holocene. Lava flows up to 18 km long have issued from summit and flank vents. Eruptions documented since 1558 CE have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. Glaciers cover 40 km2 of the volcano, and lahars have damaged towns on its flanks.

Ongoing activity

Aira, Kyushu (Japan)

31.5772°N, 130.6589°E | Summit elev. 1117 m

JMA reported ongoing activity at Minamidake Crater (Aira Caldera’s Sakurajima volcano) during 2-9 October, with incandescence at the crater observed nightly. An explosion at 2228 on 4 October produced an ash plume that rose as high as 1.5 km above the crater rim and drifted S and ejected large blocks 600-900 m from the crater. A very small eruptive event was recorded during 6-9 October. The Alert Level remained at 3 (on a 5-level scale), and the public was warned to stay 2 km away from both craters.

Geological summary: The Aira caldera in the northern half of Kagoshima Bay contains the post-caldera Sakurajima volcano, one of Japan’s most active. Eruption of the voluminous Ito pyroclastic flow accompanied formation of the 17 x 23 km caldera about 22,000 years ago. The smaller Wakamiko caldera was formed during the early Holocene in the NE corner of the caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim and built an island that was joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4,850 years ago, after which eruptions took place at Minamidake. Frequent eruptions since the 8th century have deposited ash on the city of Kagoshima, located across Kagoshima Bay only 8 km from the summit. The largest recorded eruption took place during 1471-76.

Ebeko, Paramushir Island (Russia)

50.686°N, 156.014°E | Summit elev. 1103 m

KVERT reported that moderate explosive activity at Ebeko was ongoing during 28 September-5 October. A thermal anomaly was identified in satellite images on 30 September and 2 October; weather clouds obscured views on other days. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E), explosions on 4 October generated ash plumes that rose as high as 2.5 km (8,200 ft) a.s.l and drifted to the E and SE. 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 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.

Great Sitkin, Andreanof Islands (USA)

52.076°N, 176.13°W | Summit elev. 1740 m

AVO reported that slow lava effusion at Great Sitkin was confirmed by a radar image from 3 October and likely continued through 10 October. Seismicity was characterized as low, with only a few daily earthquakes recorded by the seismic network during 3-7 October. Weakly elevated surface temperatures were identified in satellite data during 8-10 October. Weather clouds sometimes obscured views. 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 4-10 October. White-and-gray ash emissions rose as high as 1.1 km above the summit during 4-6 October and drifted in multiple directions. The Alert Level remained at a 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.

Katmai, Alaska

58.279°N, 154.9533°W | Summit elev. 2047 m

AVO reported that during 3-4 and 9 October strong winds in the vicinity of Katmai and the Valley of Ten Thousand Smokes dispersed unconsolidated ash up to 1.5 km (5,000 ft) a.s.l. to the W and SE. The ash was originally deposited during the Novarupta-Katmai eruption in 1912. The Volcano Alert Level remained at Normal (the lowest level on a four-level scale) and the Aviation Color Code remained at Green (the lowest level on a four-color scale).

Geological summary: Katmai was initially considered to be the source of the Valley of Ten Thousand Smokes ash flow in 1912. However, the 3 x 4 km caldera of 1912 is now known to have formed as a result of the voluminous eruption at nearby Novarupta volcano. The edifice had four NE-SW-trending summits, most of which were truncated by the 1912 collapse. Two or more large explosive eruptions took place during the late Pleistocene. Most of the two overlapping pre-1912 Katmai volcanoes are Pleistocene, but Holocene lava flows from a flank vent descend the SE flank of the SW edifice into the Katmai River canyon. The steep walled young caldera has a jagged rim that rises 500-1,000 m above the caldera floor and contains a deep lake. Lake waters have covered a small post-collapse lava dome (Horseshoe Island) that was seen on the caldera floor at the time of the initial ascent to the caldera rim in 1916.

Lascar, Northern Chile

23.37°S, 67.73°W | Summit elev. 5592 m

On 6 October SERNAGEOMIN reported that the Alert Level for Láscar had been lowered to Green (the lowest level on a four-color scale) because activity had returned to baseline levels. During 16-30 September sulfur dioxide gas emissions were low, averaging 565 tons per day (t/d) with a maximum of 1,109 t/d on 28 September. Passive, low-energy, whitish gas continued to be emitted, rising as high as 600 m above the crater rim on 28 September. Thermal anomalies continued to be absent in satellite data and deformation was not detected. The public was warned to stay at least 500 m away from the crater. SENAPRED declared a “preventative early warning” for San Pedro de Atacama (70 km NW) and maintained a safety perimeter of 3 km around the volcano.

Geological summary: Láscar is the most active volcano of the northern Chilean Andes. The andesitic-to-dacitic stratovolcano contains six overlapping summit craters. Prominent lava flows descend its NW flanks. An older, higher stratovolcano 5 km E, Volcán Aguas Calientes, displays a well-developed summit crater and a probable Holocene lava flow near its summit (de Silva and Francis, 1991). Láscar consists of two major edifices; activity began at the eastern volcano and then shifted to the western cone. The largest eruption took place about 26,500 years ago, and following the eruption of the Tumbres scoria flow about 9000 years ago, activity shifted back to the eastern edifice, where three overlapping craters were formed. Frequent small-to-moderate explosive eruptions have been recorded since the mid-19th century, along with periodic larger eruptions that produced ashfall hundreds of kilometers away. The largest historical eruption took place in 1993, producing pyroclastic flows to 8.5 km NW of the summit and ashfall in Buenos Aires.

Lewotolok, Lembata Island

8.274°S, 123.508°E | Summit elev. 1431 m

PVMBG reported that the eruption at Lewotolok continued during 4-10 October. White-and-gray ash plumes rose 250 m above the summit and drifted N and NW on 4 October. The next day a Volcano Observatory Notices for Aviation (VONA) was issued for a gray ash plume that rose as high as 700 m and drifted W. Ash plumes rose 200-500 m and drifted N, NW, and W on 8 and 10 October. On the other days during the week white steam-and-gas plumes were visible rising as high as 500 m and drifting N, NW, and W. At 2024 on 9 October a webcam image captured incandescent material being ejected above the summit. 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.

Mayon, Luzon (Philippines)

13.257°N, 123.685°E | Summit elev. 2462 m

PHIVOLCS reported that slow lava effusion at Mayon’s summit crater continued during 3-10 October. The lengths of the lava flow in the Mi-Isi (S), Bonga (SE), and Basud (E) drainages remained at 2.8 km, 3.4 km, and 1.1 km, respectively. Collapses at the lava dome and from the margins of the lava flows produced incandescent rockfalls and occasional pyroclastic density currents (PDCs, or pyroclastic flows) that descended the flanks as far as 4 km. Each day seismic stations recorded 92-180 rockfall events, 0-6 PDC events, and 4-30 daily volcanic earthquakes. Sulfur dioxide emissions measured almost daily averaged between 690 and 1,969 tonnes per day, with the highest value recorded on 3 October. The Alert Level remained at 3 (on a 0-5 scale) and residents were reminded to stay away from the 6-km-radius Permanent Danger Zone (PDZ). PHIVOLCS recommended that civil aviation authorities advise pilots 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.

Merapi, Central Java

7.54°S, 110.446°E | Summit elev. 2910 m

BPPTKG reported that the eruption at Merapi (on Java) continued during 29 September-5 October and seismicity remained at elevated levels. The SW lava dome produced a total of 177 lava avalanches that descended the S and SW flanks; 21 traveled as far as 1.6 km down the upper part of the Boyong drainage, 155 traveled as far as 2 km down the upper Bebeng drainage, and one traveled 700 m down the Senowo drainage. Morphological changes to the SW lava dome were due to continuing collapses of material; based on webcam images the SW dome had grown slightly taller while the dome in the summit crater remained unchanged. 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.

Nishinoshima, Izu Islands

27.247°N, 140.874°E | Summit elev. 100 m

A small eruption at Nishinoshima’s central crater was observed during an overflight conducted by the Japan Coast Guard on 4 October. Gray ash-and-gas plumes rose to 1.5 km (4,900 ft) a.s.l. Gas emissions from the central crater were at similar levels to those seen on 20 September, though gas emissions had increased at the fumaroles widely distributed along the E and N parts of the island. Dark reddish-brown-to-green discolored water was visible around most of the island.

Geological summary: The small island of Nishinoshima was enlarged when several new islands coalesced during an eruption in 1973-74. Multiple eruptions that began in 2013 completely covered the previous exposed surface and continued to enlarge the island. The island is the summit of a massive submarine volcano that has prominent peaks to the S, W, and NE. The summit of the southern cone rises to within 214 m of the ocean surface 9 km SSE.

Popocatepetl, Mexico

19.023°N, 98.622°W | Summit elev. 5393 m

CENAPRED reported that eruptive activity continued at Popocatépetl during 3-10 October. Long-period events totaling 54-590 per day were accompanied by steam-and-gas plumes that sometimes contained minor amounts of ash. Some of the plumes drifted NW and W; cloudy weather conditions prevented visual observations on several of the days. The Alert Level remained at Yellow, Phase Two (the middle level on a three-color scale) and the public was warned to stay 12 km away from the crater.

Geological summary: Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America’s 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

Semeru, Eastern Java

8.108°S, 112.922°E | Summit elev. 3657 m

PVMBG reported that eruptive activity continued at Semeru during 4-10 October. Weather conditions sometimes prevented visual observations. Dense white-and-gray ash plumes rose 500-700 m above the summit and drifted S and SW at 0710 on 5 October and 0704 on 9 October. White steam-and-gas plumes were visible rising 200 m above the summit and drifting S, SW, W, and NW on 7 October. Eruptive events at 0759, 1852, and 1933 on 10 October produced dense white-and-gray ash plumes that rose 400-500 m and drifted N. The Alert Level remained at 3 (third highest 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 28 September-5 October. Thermal anomalies were identified in satellite images during 28-29 September and 1-2 and 5 October; observations on other days were obscured by weather clouds. 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.

Shishaldin, Fox Islands (USA)

54.756°N, 163.97°W | Summit elev. 2857 m

AVO reported that the eruption at Shishaldin continued during 4-10 October. After the significant explosive event on 3 October, ash plumes continued to be produced for over eight hours until around 1400. Hot rock avalanches had descended the SW and NE flanks; two explosion craters located at the base of the NE deposits, about 3.2 km from the crater rim, were the sources of persistent ash. During 3-4 October small, local ash plumes from occasional collapse events were visible in webcam images. Seismicity remained elevated during 4-10 October with small frequent earthquakes. Gas emissions were occasionally visible, though weather clouds occasionally prevented views. Elevated surface temperatures were identified in satellite images during 8-10 October. 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 symmetrical glacier-covered Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. It is the westernmost of three large stratovolcanoes in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning “mountain which points the way when I am lost.” Constructed atop an older glacially dissected edifice, it is largely basaltic in composition. Remnants of an older ancestral volcano are exposed on the W and NE sides at 1,500-1,800 m elevation. There are over two dozen pyroclastic cones on its NW flank, which is blanketed by massive aa lava flows. Frequent explosive activity, primarily consisting of Strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century. A steam plume often rises from the summit crater.

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 2-9 October. Crater incandescence was visible nightly, and blocks were ejected as far as 600 m from the crater. Explosions at 0304, 2141, and 2359 on 2 October, at 0112 on 3 October, and 1326 on 6 October produced ash plumes that rose as high as 1 km above the crater rim and drifted SW and W. An explosion was recorded at 0428 on 3 October, though emission details were unknown. 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.

Ubinas, Peru

16.355°S, 70.903°W | Summit elev. 5672 m

Instituto Geofísico del Perú (IGP) reported that the eruption at Ubinas continued during 3-9 October at low to moderate levels. There were daily averages of 155 volcano-tectonic earthquakes indicating rock fracturing and 27 long-period earthquakes signifying the movement of gas and magma. In addition, seismic signals associated with ash emissions were recorded for a total of 25 hours during the week. On 4 October IGP reported that an ash plume drifted more than 15 km SW and S. According to the Washington VAAC small, diffuse ash plumes identified in satellite images drifted N, E, SE, and S at altitudes of 5.5-7.6 km (18,000-25,000 ft) a.s.l. during 4-8 October. IGP noted that on 7 October a steam, gas, and ash plume rose as high as 1.9 km above the crater rim and drifted NE, E, and SE. The Alert Level remained at Orange (the third level on a four-color scale) and the public was warned to stay 4 km away from the crater.

Geological summary: A small, 1.4-km-wide caldera cuts the top of Ubinas, Perú’s most active volcano, giving it a truncated appearance. It is the northernmost of three young volcanoes located along a regional structural lineament about 50 km behind the main volcanic front. The growth and destruction of Ubinas I was followed by construction of Ubinas II beginning in the mid-Pleistocene. The upper slopes of the andesitic-to-rhyolitic Ubinas II stratovolcano are composed primarily of andesitic and trachyandesitic lava flows and steepen to nearly 45 degrees. The steep-walled, 150-m-deep summit caldera contains an ash cone with a 500-m-wide funnel-shaped vent that is 200 m deep. Debris-avalanche deposits from the collapse of the SE flank about 3,700 years ago extend 10 km from the volcano. Widespread Plinian pumice-fall deposits include one of Holocene age about 1,000 years ago. Holocene lava flows are visible on the flanks, but historical activity, documented since the 16th century, has consisted of intermittent minor-to-moderate explosive eruptions.

Whakaari/White Island, North Island (New Zealand)

37.52°S, 177.18°E | Summit elev. 294 m

On 10 October GeoNet reported that activity at Whakaari/White Island was characterized by minor steam-and-gas emissions during the past few months based on gas and observational overflights. The active vents located on the W shore of the lake continued to produce steam-and-gas plumes that were sometimes tall (particularly on 8 October) due to local atmospheric conditions. Gas emissions were within normal ranges and there was no evidence of ash emissions or eruptions. Temperatures at the larger vents declined from more than 240 degrees Celsius in March, around 120 degrees during June-August, to 95 degrees in October. Minor morphological changes were due to erosion. During a 4 October observation flight scientists saw a rockfall from Troup Head on the E end of the island, with rocks descending both the N and S sides of the ridge. The Volcanic Alert Level remained at 2 (on a scale of 0-5) and the Aviation Color Code remained at Yellow (the second level on a four-color scale). GeoNet noted that Alert Levels reflect the level of unrest at the volcano but also consider the greater level of uncertainty due to the current lack of consistent and useful real-time data.

Geological summary: The uninhabited Whakaari/White Island is the 2 x 2.4 km emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes. The SE side of the crater is open at sea level, with the recent activity centered about 1 km from the shore close to the rear crater wall. Volckner Rocks, sea stacks that are remnants of a lava dome, lie 5 km NW. Descriptions of volcanism since 1826 have included intermittent moderate phreatic, phreatomagmatic, and Strombolian eruptions; activity there also forms a prominent part of Maori legends. The formation of many new vents during the 19th and 20th centuries caused rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project. Explosive activity in December 2019 took place while tourists were present, resulting in many fatalities. The official government name Whakaari/White Island is a combination of the full Maori name of Te Puia o Whakaari (“The Dramatic Volcano”) and White Island (referencing the constant steam plume) given by Captain James Cook in 1769.

References:

Smithsonian Institution / US Geological Survey Weekly Volcanic Activity Report – October 4 – 10, 2023 – Managing Editor: Sally Sennert.

Featured image credit: The Watchers

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