The Weekly Volcanic Activity Report: September 13 - 19, 2023

New activity/unrest was reported for 2 volcanoes from September 13 to 19, 2023. During the same period, ongoing activity was reported for 21 volcanoes.

New activity/unrest: Kilauea, Hawaiian Islands (USA) | Ruby, Mariana Islands (USA).

New activity/unrest

Kilauea, Hawaiian Islands (USA)

19.421°N, 155.287°W | Summit elev. 1222 m

HVO reported that the eruption located at the W side of the down-dropped block within Kilauea’s Halema`uma`u Crater had ceased after activity declined over a few days. During 12-14 September multiple active vents, that were roughly E-W-trending and spanned a distance of about 750 m, produced lava fountains that rose as high as 10 m. Ramparts built by spatter were almost 20 m tall on the S sides (downwind side) of the vents. Lava from the vents flowed onto the N and W parts of the crater floor on 12 September, onto the N and E parts on 13 September, and only onto the W part by 14 September; the distances of the active flows progressively decreased. The area N of the active vents had become perched and was 3 m higher than the surrounding surface. Sulfur dioxide emissions averaged 20,000 tonnes per day (t/d) on the afternoon of 13 September, down significantly from 190,000 t/d measured just after the onset of the eruption. Effusion rates had decreased but remained at high levels.

Vigorous spattering and lava fountains that rose 10-15 m were visible at the westernmost large spatter cone during 14-15 September. Minor spattering at the next cone to the E did not rise above its rim. Lava continued to flow from the vents and travel N and W, confined to the W part of the down-dropped block and the NE parts of Halema`uma`u. A laser rangefinder pointed at the W portion of the crater continued to record uplift from the magmatic intrusion beneath the caldera since the onset of the eruption; the total local uplift was 6 m by 13 September, 9 m by 14 September, and 10 m by 15 September. Field crews observed that eruptive activity had greatly diminished or ceased at several of the vents by the morning of 15 September. Lava was no longer flowing onto the crater floor but active lava was ponded in an area N of the vents. Intermittent spattering was visible overnight at the large, westernmost cone but beginning at around 0700 on 16 September webcam images recorded minor to no fountaining. By 1115 spattering ceased and by noon the ponded lava had stagnated. Tremor levels indicting fluid movement decreased during 15-16 September and retuned to pre-eruption levels by 1700 on 16 September. Sulfur dioxide emission rates had also decreased and were 800 t/d by 16 September, only slightly above the 100-200 t/d typical of non-eruptive periods. At 0902 on 17 September HVO lowered the Volcano Alert Level to Advisory (the second level on a four-level scale) and the Aviation Color Code was lowered to Yellow (the second color on a four-color scale).

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.

Ruby, Mariana Islands (USA)

15.605°N, 145.572°E | Summit elev. -209 m

The US Geological Survey reported that an eruption began at Ruby on 15 September. A submarine plume of discolored water was identified in satellite images at around 0650 but there was no activity above the water surface. Eruption signals began at 1427 on 15 September based on retrospective analysis of seismo-acoustic data from a geophysical monitoring station on Saipan, 50 km SE. The activity was also recorded on other regional geophysical monitoring networks in the Pacific. The submarine plume had detached from the source vent by the morning of 16 September and no additional activity was recorded by geophysical networks. The Volcano Alert Level was raised to Advisory (the second level on a four-level scale) and the Aviation Color Code was raised to Yellow (the second level on a four-color scale).

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). In 1995 submarine explosions were heard, accompanied by a fish kill, sulfurous odors, bubbling water, and the detection of volcanic tremor.

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 11-18 September and incandescence at the crater was observed nightly. Sulfur dioxide emissions averaged 1,900 tons per day on 11 September. An explosion at 0018 on 11 September produced an ash plume that rose 1.1 km above the crater rim and ejected large blocks 300-500 m from the crater. An eruptive event at 1642 produced an ash plume that rose 1.3 km. At 2211 on 13 September an explosion produced an ash plume that rose 1.7 km and drifted N and ejected large blocks 500-700 m from the crater. 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.

Dukono, Halmahera

1.6992°N, 127.8783°E | Summit elev. 1273 m

PVMBG reported that the eruption at Dukono was ongoing during 13-17 September. Dense white-and-gray plumes rose as high as 350 m above the summit and drifted E and W. The Alert Level remained at Level 2 (on a scale of 1-4), and the public was warned to remain outside of the 2-km exclusion zone.

Geological summary: Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia’s most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, have occurred since 1933. During a major eruption in 1550 CE, a lava flow filled in the strait between Halmahera and the N-flank Gunung Mamuya cone. This complex volcano presents a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also been active during historical time.

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 7-14 September. A thermal anomaly was identified in satellite images during 9-11 September; weather clouds obscured views on other days. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E), explosions during 10-11 and 13-14 September generated ash plumes that rose as high as 3 km (10,000 ft) a.s.l and drifted to the E. 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.

Fuego, South-Central Guatemala

14.473°N, 90.88°W | Summit elev. 3763 m

INSIVUMEH reported that 4-10 explosions per hour were recorded at Fuego during 13-19 September, generating ash-and-gas plumes that rose as high as 1.1 km above the crater rim. The ash plumes drifted as far as 30 km W and SW, causing minor ashfall in areas downwind including Morelia (9 km SW), Panimaché I and II (8 km SW), Palo Verde (10 km WSW), Sangre de Cristo (8 km W), El Porvenir (8 km SE), and Yepocapa (9 km WNW). Daily shock waves rattled structures in communities around the volcano and rumbling was often heard. Explosions caused daily block avalanches to descend the Ceniza (SSW), Seca (W), Trinidad (S), Taniluyá (SW), Honda, Las Lajas (SE), and/or El Jute (ESE) drainages. The explosions also ejected incandescent material as high as 200 m above the summit.

Geological summary: Volcán Fuego, one of Central America’s most active volcanoes, is also one of three large stratovolcanoes overlooking Guatemala’s former capital, Antigua. The scarp of an older edifice, Meseta, lies between Fuego and Acatenango to the north. Construction of Meseta dates back to about 230,000 years and continued until the late Pleistocene or early Holocene. Collapse of Meseta may have produced the massive Escuintla debris-avalanche deposit, which extends about 50 km onto the Pacific coastal plain. Growth of the modern Fuego volcano followed, continuing the southward migration of volcanism that began at the mostly andesitic Acatenango. Eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks. Frequent vigorous historical eruptions have been recorded since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows.

Gamalama, Halmahera

0.81°N, 127.3322°E | Summit elev. 1714 m

Although there was no eruptive activity reported, in a 19 September press release, PVMBG noted that the number of daily deep volcanic earthquakes at Gamalama increased in early September and remained above average. The seismic network recorded a total of 16 deep volcanic earthquake events on 8 September and an average of nine events per day through 18 September; 1-2 events per day are generally recorded. The number of earthquakes indicating emissions also increased during 8-18 September, though diffuse white plumes only rose as high as 100 m above the summit whereas typically they can rise as high as 300 m. PVMBG noted that the most likely hazard would be a phreatic event that could ejected material within the 1.5-km radius, though ash may be carried farther by wind. The Alert Level remained at 2 (on a scale of 1-4); visitors and residents were warned not to approach the crater within a 1.5-km radius.

Geological summary: Gamalama is a near-conical stratovolcano that comprises the entire island of Ternate off the western coast of Halmahera, and is one of Indonesia’s most active volcanoes. The island was a major regional center in the Portuguese and Dutch spice trade for several centuries, which contributed to the extensive documentation of activity. Three cones, progressively younger to the north, form the summit. Several maars and vents define a rift zone, parallel to the Halmahera island arc, that cuts the volcano; the S-flank Ngade maar formed after about 14,500–13,000 cal. BP (Faral et al., 2022). Eruptions, recorded frequently since the 16th century, typically originated from the summit craters, although flank eruptions have occurred in 1763, 1770, 1775, and 1962-63.

Great Sitkin, Andreanof Islands (USA)

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

AVO reported that slow lava effusion likely continued at Great Sitkin during 13-19 September, producing a thick flow in the summit crater that mainly expanded E. A few daily earthquakes were recorded by the seismic network and seismicity was characterized as low. Weather clouds often prevented satellite and webcam observations, though no activity was observed on a few of the days with partly cloudy weather. 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.

Karangetang, Sangihe Islands

2.781°N, 125.407°E | Summit elev. 1797 m

PVMBG reported that dense white gas-and-steam plumes from Karangetang were visible on most days during 13-19 September rising as high as 300 m above Main and North craters and drifting mainly NW, N, and NE. Weather clouds sometimes prevented views of the summit. According to news articles, seismicity during 1-7 September indicated lava from the SW side of Main Crater (S crater) continued to effuse but at a decreased rate, and that the number of earthquakes indicating avalanches had also decreased, according to PVMBG. Lava avalanches traveled as far as 1.5 km down the Batuawang and Kahetang drainages on the S flank and rarely descended the SW flank. Lava effusion at Main Crater was not visible during 8-15 September, though sounds of avalanches were sometimes intense, and rumbling was also occasionally heard. Incandescence emanated from both Main and North craters. The number of avalanches continued to decrease. The Alert Level remained at 3 (on a scale of 1-4) and the public were advised to stay 2.5 km away from Main Crater with an extension to 3.5 km on the S and SE flanks.

Geological summary: Karangetang (Api Siau) volcano lies at the northern end of the island of Siau, about 125 km NNE of the NE-most point of Sulawesi. The stratovolcano contains five summit craters along a N-S line. It is one of Indonesia’s most active volcanoes, with more than 40 eruptions recorded since 1675 and many additional small eruptions that were not documented (Neumann van Padang, 1951). Twentieth-century eruptions have included frequent explosive activity sometimes accompanied by pyroclastic flows and lahars. Lava dome growth has occurred in the summit craters; collapse of lava flow fronts have produced pyroclastic flows.

Klyuchevskoy, Central Kamchatka (Russia)

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

KVERT reported that the explosive Strombolian eruption at Klyuchevskoy continued during 7-14 September. A daily bright thermal anomaly was identified in satellite images. Lava fountaining fed flows that advanced down the Apakhonchichsky and Kozyrevsky drainages on the SE flank. Plumes of resuspended ash drifted 550 km E and SE during 9-11 September. The Aviation Color Code remained at Yellow (the second level on a four-color scale). Dates are based on UTC times; 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.

Lewotolok, Lembata Island

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

PVMBG reported that the eruption at Lewotolok continued during 12-19 September. According to the Darwin VAAC an ash plume rose 600 m above the summit and drifted WNW on 12 September. PVMBG noted that white-and-gray plumes rose 250-400 m above the summit and drifted W and NW on 13 and 16 September. White steam-and-gas plumes rose as high as 300 m and drifted W and NW on the other days. Webcam images captured incandescent material being ejected above the summit at 0101 on 13 September and summit incandescence at 1830 on 16 September. 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 the eruption at Mayon continued during 12-19 September. 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 rockfalls and pyroclastic density currents (PDCs, or pyroclastic flows) that descended the flanks as far as 4 km. Each day seismic stations recorded 101-160 rockfall events, 1-6 PDC events, and 3-12 daily volcanic earthquakes. During 12-13 September the volcanic earthquake signals included one indicating an ash emission and a tremor event that lasted one minute. Daily sulfur dioxide emissions averaged between 765 and 1,551 tonnes per day, with the highest value recorded on 16 September. Electronic Distance Measuring (EDM), precise leveling, continuous GPS, and electronic tilt monitoring data showed that the volcano remained generally inflated relative to baseline levels; tilt and GPS monitoring data indicated pronounced inflation of the mid SE flank since the beginning of August 2023. 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 8-14 September and seismicity remained at elevated levels. The SW lava dome produced a total of 162 lava avalanches that descended the S and SW flanks; 10 traveled as far as 1.5 km down the upper part of the Boyong drainage, 151 traveled as far as 2 km down the upper Bebeng drainage, and one traveled 1.2 km down the Sat/Putih drainage. Morphological changes to the SW lava dome were due to continuing 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.

Santa Maria, Southwestern Guatemala

14.757°N, 91.552°W | Summit elev. 3745 m

INSIVUMEH reported that eruptive activity continued at Santa Maria’s Santiaguito lava dome complex during 12-19 September. Incandescence from the dome was visible during most nights and early mornings, and occasionally from the lava flow on the WSW flank. Lava extrusion continued. Daily weak-to-moderate explosions generated gas-and-ash plumes that rose 900-1,000 m above the dome and drifted NW, W, and SW. Some explosions triggered incandescent avalanches that descended the dome’s flanks in all directions, and occasionally into drainages on the S, SE, and E flanks. Deposits from block-and-ash-flows accumulated on top of the lava flows in the Zanjón, Seco, and San Isidro drainages.

Geological summary: Symmetrical, forest-covered Santa María volcano is part of a chain of large stratovolcanoes that rise above the Pacific coastal plain of Guatemala. The sharp-topped, conical profile is cut on the SW flank by a 1.5-km-wide crater. The oval-shaped crater extends from just below the summit to the lower flank, and was formed during a catastrophic eruption in 1902. The renowned Plinian eruption of 1902 that devastated much of SW Guatemala followed a long repose period after construction of the large basaltic-andesite stratovolcano. The massive dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four vents, with activity progressing W towards the most recent, Caliente. Dome growth has been accompanied by almost continuous minor explosions, with periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.

Semeru, Eastern Java

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

PVMBG reported that eruptive activity continued at Semeru during 13-19 September. White-and-gray ash plumes rose 200-300 m above the summit and drifted W on 14 September. According to the Darwin VAAC a diffuse ash plume was identified in a satellite image rising to 4.2 km (14,000 ft) a.s.l. (610 m above the summit) and drifting SW at 0640 on 15 September. 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 7-14 September. Thermal anomalies were identified in satellite images on all days except 14 September (due to weather clouds). Plumes of resuspended ash drifted 160 km SE and E during 9-11 September. 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 13-19 September. Eruptive activity increased during 13-14 September. Elevated surface temperatures began to be identified in satellite images during the afternoon of 13 September and they increased later that night. Seismic tremor amplitudes began to increase at around 1800 and small explosions were detected in seismic and infrasound data. Incandescent lava at the summit was seen in a webcam image at 0134 on 14 September during a period of elevated tremor. No ash emissions were visible though high weather clouds may have obscured them.

Seismic tremor began to increase sometime around 0900 on 15 September and rapidly intensified. An explosive eruption began at around 1710, prompting AVO to the Aviation Color Code to Red (the highest color on a four-color scale) and the Volcano Alert Level to Warning (the highest level on a four-level scale). Within about 30 minutes ash plumes drifted E below a weather cloud deck at 8.2 km (27,000 ft) a.s.l., unseen in satellite views. The National Weather Service estimated that an ash-rich plume rose as high as 12.8 km (42,000 ft) a.s.l. and produced volcanic lightning. The upper parts of the plume detached by 1830, at about the same time that seismicity dramatically decreased. Lightning was again detected beginning around 1930, suggesting that ash emissions continued. Ongoing explosions were detected in infrasound data, at a lower level than during the most energetic phase of this event. Trace amounts of ash fell in False Pass (38 km ENE) during 1800-2030. Lightning was last detected at 2048. By 2124 the intensity of the eruption had decreased, and ash emissions were likely rising to altitudes less than 6.7 km (22,000 ft) a.s.l. Seismicity returned to pre-eruption levels; at 1244 on 16 September AVO lowered the Volcano Alert Level to Watch and the Aviation Color Code to Orange. A plume of sulfur dioxide emitted during 14-15 September was detected over the North Pacific. Seismicity remained elevated with tremor and small daily earthquakes occurring over 16-18 September. Elevated surface temperatures at the summit were identified in satellite data and minor steam emissions were visible in webcam views.

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 11-18 September. Eruptive events at 0511 and 1228 on 15 September produced ash plumes that rose 1-1.8 km above the crater rim and drifted N and NW, respectively. Blocks were ejected as far as 300 m from the crater. 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.

Taal, Luzon (Philippines)

14.0106°N, 120.9975°E | Summit elev. 311 m

PHIVOLCS reported ongoing unrest at Taal during 13-18 September. Daily emissions of gas-and-steam rose from Main Crater Lake generally as high as 2.4 km, were sometimes voluminous, and drifted ENE, ESE, SW, and NW. Upwelling gasses and fluids in the lake were visible during daily observations. During 14-18 September there were 2-4 daily volcanic earthquakes recorded by the seismic network, including 1-3 daily periods of tremor each lasting 1-2 minutes long. Sulfur dioxide emissions averaged 3,264 tonnes per day on 15 September and coupled with taller steam-and-gas plumes that rose as high as 3 km, caused vog over Taal Lake beginning at around 1000. PHIVOLCS noted that vog had been affecting the Taal region since the first week of September. The Alert Level remained at 1 (on a scale of 0-5), and PHIVOLCS reminded the public that the entire Taal Volcano Island was a Permanent Danger Zone (PDZ).

Geological summary: Taal is one of the most active volcanoes in the Philippines and has produced some powerful eruptions. The 15 x 20 km Talisay (Taal) caldera is largely filled by Lake Taal, whose 267 km2 surface lies only 3 m above sea level. The maximum depth of the lake is 160 m, with several submerged eruptive centers. The 5-km-wide Volcano Island in north-central Lake Taal is the location of all observed eruptions. The island is composed of coalescing small stratovolcanoes, tuff rings, and scoria cones. Powerful pyroclastic flows and surges have caused many fatalities.

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 11-17 September at low-to-moderate levels. There were daily averages of 144 volcano-tectonic earthquakes indicating rock fracturing and 86 long-period earthquakes signifying the movement of gas and magma. One explosion was recorded on 14 September. INGEMMET noted that sulfur dioxide emissions were at low levels during 14-15 September, averaging 900 tons per day. Ash-and-steam plumes rose 1.6 km above the crater rim and drifted SE and NE, causing ashfall in areas within 5 km downwind. IGP noted that seismic signals associated with ash emissions were recorded for an average of three hours per day during 14-16 September. Ash, gas, and steam emissions visible in webcam images rose as high as 2.6 km above the crater rim and drifted as far as 15 km NE, E, and SE. Deformation data indicated a slight trend of inflation with variations less than 5 mm. 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.

Ulawun, New Britain (Papua New Guinea)

5.05°S, 151.33°E | Summit elev. 2334 m

Rabaul Volcano Observatory (RVO) reported a small eruption at Ulawun during 14-15 September. Minor incandescence at the summit crater was first visible at around 2107 on 14 September from Ulamona Observatory. The incandescence intensified, and eruption plumes reflecting the glow were visible in webcam images drifting NE. Starting at about 0004 and lasting to about 0800 on 15 September there were brief periods when the plumes appeared darker, likely due to denser and more intense emissions. The plumes drifted W and WSW. Rumbling noises were reported, though they became less frequent by 0800. The Alert Level was raised to Stage 2 (the second level on the four-level scale).

Staff from the West New Britain Provincial Disaster Office conducted a field inspection on 15 September and found only minor ashfall around the volcano. During 0800 on 15 September to 1430 on 19 September the volcano was quiet; small volumes of diffuse white emissions sometimes rose from the summit and drifted W and WSW. On 19 September RVO recommended that the Alert Level should be lowered to Stage 1.

Increased seismicity coincided with the eruption. During most of 14 September RSAM values were 200-300, though they began to increase at about 1955 and reached a value of around 800 by midnight. RSAM continued to increase; values reached 1,600 by 0100 on 15 September, rapidly increased during 0100-0200, and reached a value of 4,060 almost two hours later at 0300. Seismicity was dominated by continuous low-frequency volcanic tremors. Seismicity began to decline at 0700, reached background levels by 0900, and remained low with values of 200-450. During 16-19 September seismicity was characterized by low level volcanic tremors with sporadic occurrences of discrete, small, low-frequency volcanic events. RSAM values were around 200.

Geological summary: The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea’s most frequently active. The volcano, also known as the Father, rises above the N coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1,000 m is unvegetated. A prominent E-W escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and E flanks. A steep-walled valley cuts the NW side, and a flank lava-flow complex lies to the south of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater.

Villarrica, Central Chile

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

SERNAGEOMIN reported that the eruption in Villarrica’s summit crater was ongoing during 13-19 September. Long-period (LP) earthquakes were recorded at 0622 on 15 September and at 0426 and 0723 on 16 September; weather conditions prevented views of the summit during these events. An LP earthquake at 0130 on 18 September was associated with crater incandescence and a gas-and-steam plume that rose 120 m above the crater rim. The Volcanic Alert level remained at Yellow (the second highest on a four-level scale) according to SERNAGEOMIN and the public was warned to stay 500 m 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.

Yasur, Vanuatu

19.532°S, 169.447°E | Summit elev. 361 m

Vanuatu Meteorology and Geohazards Department (VMGD) reported that Yasur emitted a substantial ash cloud during 1400-1700 on 12 September based on reports from nearby observers. The plumes drifted SE; VMGD warned that areas around White Sands, 3 km N, may experience impacts from ashfall and gas. The volcano had returned to normal levels by the next day. The Alert Level remained at 2 (the middle level on a scale of 0-4).

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:

Smithsonian Institution / US Geological Survey Weekly Volcanic Activity Report – September 13 – 19, 2023 – Managing Editor: Sally Sennert.

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