The Weekly Volcanic Activity Report: August 13-19, 2026

New activity/unrest: Asosan, Japan | Etna, Italy | Karangetang, Indonesia | Klyuchevskoy, Russia | Krakatau, Indonesia | Sinabung, Indonesia.

Ongoing activity: Aira, Japan | Ambae, Vanuatu | Dukono, Indonesia | Great Sitkin, United States | Ibu, Indonesia | Kanlaon, Philippines | Kilauea, United States | Lewotobi, Indonesia | Lewotolok, Indonesia | Mayon, Philippines | Merapi, Indonesia | Nyamulagira, DR Congo | Rincon de la Vieja, Costa Rica | Sabancaya, Peru | Semeru, Indonesia.

New activity/unrest

Asosan, Japan

32.8849°N, 131.085°E; Elev. 1,592 m

The Japan Meteorological Agency (JMA) reported that the amplitude of volcanic tremors at Asosan began to increase at around 1900 on 12 August, fluctuated for a few days, and further intensified at 1500 on 14 August. During a field survey that same day scientists measured a high sulfur dioxide emission rate of 2,700 tons per day (t/d), notably increased from 700 t/d on 28 July and 1,200 t/d on 6 August. The Alert Level was raised to 3 (on a scale of 1-5) at 1545 and the public was warned that eruptive products may impact areas within 2 km of the crater. Continuous Global Navigation Satellite System (GNSS) data suggested that magma was accumulating beneath Kusasenri. Webcams show no significant changes in conditions within the crater; white plumes rose as high as 900 m above the Nakadake Crater I rim during 12-17 August.

Geological summary: The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan’s most active volcanoes. It was the location of Japan’s first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu’s most popular tourist destinations.

Etna, Italy

37.748°N, 14.999°E; Elev. 3,357 m

The Sezione di Catania – Osservatorio Etneo (INGV) reported eruptive activity at Etna’s summit craters during 10-16 August characterized by explosive activity and ash emissions at both Voragine Crater (VOR) and Northeast Crater (NEC), and effusive activity from several vents within the Valle del Bove. Explosive activity at VOR persisted during most of the week with ash emissions mainly drifting S and SE. Emissions significantly intensified during the afternoon of 13 August and Strombolian activity was visible the afternoon of 16 August. Explosive activity on 17 August generated a notable ash plume that rose around 6 km (19,700 ft) a.s.l. and drifted SE. Several intra-crater explosive episodes at NEC were recorded during the week. A brief explosion on 15 August produced an ash plume that drifted S. A series of short-lived explosions on 16 August produced ash plumes that drifted SE. Ash emissions intensified later that day.

Lava effusion from multiple vents was variable through the week. During 10-12 August flows from vents at 1,900 m, 2,090 m, and 2,750 m elevations were active, though by 13 August effusion at the 2,090 m elevation vent had ceased. Early on 14 August a pit crater formed at an elevation of 3,000 m and produced intermittent gas emissions for a brief period. Strombolian activity continued and the leading lava flows from the active vents advanced during 13-16 August, reaching an elevation of 1,395 m between Rocca delle Palombe and Rocca Musarra. On 17 August a new effusive vent opened in Valle del Bove, at an elevation of 2,350 m, which triggered the collapse of the E flank of the Monte Rittmann cone along with an ash emission. The new vent produced a lava flow that traveled 500 m and rapidly cooled. By the afternoon of 17 August, the lava field fed by multiple vents was generally cooling. The vent at 1,900 m elevation remained active and continued to effuse lava with the flow front reaching an elevation of approximately 1,600 m. Overall effusion during 7-17 August covered an approximate area of 1.7 square kilometers and had estimated volumes ranging from 5.6 to 7.6 × 10⁶ cubic meters. The volcano Alert Level remained at Yellow (the second lowest level on a four-level scale) according to the Dipartimento della Protezione Civile.

Geological summary: Mount Etna, towering above Catania on the island of Sicily, has one of the world’s longest documented records of volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.

Karangetang, Indonesia

2.781°N, 125.407°E; Elev. 1,797 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) and a news source reported that an eruption at Karangetang’s North Crater (Kawah Dua) continued during 12-19 August. Lava began to effuse from North Crater on 9 August, advancing about 700 m S into the saddle between the North and South (Kawah Utama or Main) craters, then advanced W for about 400 m and NNW for about 1 km, igniting vegetation fires. Lava flows continued to be active during 12-18 August and descended 1 km SW. Rumbling was often heard, which was sometimes accompanied by grayish-white puffs that rose as high as 150 m and drifted NNE. Residents in Pehe Village reported that vegetation between the Kinali and Hiung rivers had ignited and was burning. The Alert Level remained at 2 (on a scale of 1-4) and the public was advised to stay 1.5 km away from both craters, with an extension to 2.5 km on the NW and SW flanks of North Crater.

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, Russia

56.056°N, 160.642°E; Elev. 4,754 m

The Kamchatkan Volcanic Eruption Response Team (KVERT) reported that a new eruption at Klyuchevskoy began with Strombolian explosions and lava fountaining at the summit crater on 15 August. The temperature of a thermal anomaly identified in satellite images began increasing at 1541. Activity continued on 16 August and at 2236 the Aviation Color Code (ACC) was raised to Yellow (the second lowest level on a four-color scale). A series of large collapses began in the Apakhonchichsky drainage on the SE flank at 2320 and lasted about 30 minutes. Ash clouds from the collapse and possible explosions rose 7-8 km (22,960-26,250 ft) a.s.l. and drifted 50 km E, though according to the Tokyo Volcanic Ash Advisory Center (VAAC) ash plumes may have risen as high as 9.1 km (30,000 ft) a.s.l. The ACC was raised to Orange at 2343. Strombolian explosions and lava fountaining continued on 17 August and collapsed hot material descended the Apakhonchichsky drainage. Ash plumes rose 6 km (19,680 ft) a.s.l. and drifted 420 km ESE. Gas-and-ash plumes rose to 5.5 km (18,100 ft) a.s.l. on 18 August and drifted 400 km ESE. Dates and times are provided in Coordinated Universal Time (UTC); specific events are indicated in local time where specified.

Geological summary: Klyuchevskoy is the highest and most active volcano on the Kamchatka Peninsula. Since its origin about 6,000 years ago, this symmetrical, basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during approximately the past 3,000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 and 3,600 m elevation. Eruptions recorded since the late 17th century have resulted in frequent changes to the morphology of the 700-m-wide summit crater. These eruptions over the past 400 years have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

Krakatau, Indonesia

6.1009°S, 105.4233°E; Elev. 285 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported ongoing eruptive activity at Krakatau during 13-20 August. White-and-gray plumes rose as high as 150 m above the summit on 13 August and drifted in various directions. No emissions were observed the next day. During 16-18 August white, gray, and black plumes rose as high as 400 m above the summit and drifted mainly NW, N, NE, and E. Multiple eruptive events per day were recorded during 16-17 August, and several webcam images showed incandescent material being ejected above the crater. According to a news report, residents of Tejang Village (20 km NNE) on Sebesi Island reported ashfall during 16-18 August and adverse health effects due to ash in the air. The Alert Level remained at 3 (on a scale of 1-4) and the public was advised to stay 3 km away from summit.

Geological summary: The renowned Krakatau (frequently misnamed as Krakatoa) volcano lies in the Sunda Strait between Java and Sumatra. Collapse of an older edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of that volcano are preserved in Verlaten and Lang Islands; subsequently the Rakata, Danan, and Perbuwatan cones were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption caused more than 36,000 fatalities, most as a result of tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former Danan and Perbuwatan cones. Anak Krakatau has been the site of frequent eruptions since 1927.

Sinabung, Indonesia

3.17°N, 98.392°E; Elev. 2,460 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that seismicity at Sinabung is continuing to increase. There was a notable increase in the number of deep volcanic earthquakes and signals indicating emissions during 1-12 August. Additionally, some low-frequency and hybrid earthquakes were detected. Emissions had become denser, were grayish-white, and rose as high as 1 km above the summit. The Alert Level remained at 2 (on a scale of 1-4), though at 1000 on 13 August the exclusion zone was increased to 3 km from the summit and 4.5 km on the SE flank.

Geological summary: Gunung Sinabung is a Pleistocene-to-Holocene stratovolcano with many lava flows on its flanks. The migration of summit vents along a N-S line gives the summit crater complex an elongated form. The youngest crater of this conical andesitic-to-dacitic edifice is at the southern end of the four overlapping summit craters. The youngest deposit is a SE-flank pyroclastic flow 14C dated by Hendrasto et al. (2012) at 740-880 CE. An unconfirmed eruption was noted in 1881, and solfataric activity was seen at the summit and upper flanks in 1912. No confirmed historical eruptions were recorded prior to explosive eruptions during August-September 2010 that produced ash plumes to 5 km above the summit.

Ongoing activity

Aira, Japan

31.5772°N, 130.6589°E; Elev. 1,117 m

The Japan Meteorological Agency (JMA) reported ongoing eruptive activity at Minamidake Crater (Aira Caldera’s Sakurajima volcano) during 10-17 August. Crater incandescence was visible in nighttime webcam images. The monitoring networks recorded a total of 14 eruptive events and one explosion. Eruptive events during 10-15 August generated ash plumes that rose as high as 1.8 km above the summit and drifted in multiple directions. Emissions were sometimes continuous, notably during 0020-0150 on 12 August, during 1906-2220 on 14 August, and during 1019-1150 on 15 August. An explosion at 2232 on 13 August ejected large blocks 800-1,100 m from the vent; plume characteristics were not reported. The Alert Level remained at 3 (on a 5-level scale), and the public was warned to be cautious within 2 km of both the Minimadake and Showa 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.

Ambae, Vanuatu

15.389°S, 167.835°E; Elev. 1,496 m

The Wellington Volcanic Ash Advisory Center (VAAC) reported that daily ash-and-gas plumes at Ambae were identified in satellite and webcam images during 13-18 August rising 1.5-4.6 km (5,000-15,000 ft) a.s.l. and drifting in multiple directions. Occasionally the ash emissions were intermittent, and sulfur dioxide plumes were also occasionally identified. Weather clouds sometimes obscured views. The Alert Level remained at 3 (on a scale of 0-5), and the public was warned to stay outside of Danger Zone B, defined as a 3-km radius around the active vents in Lake Voui, and to stay 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 with numerous 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.

Dukono, Indonesia

1.6992°N, 127.8783°E; Elev. 1,273 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that eruptive activity at Dukono continued during 13-19 August. White plumes rose as high as 400 m above the summit on 13 August. On the other days white-and-gray ash plume rose as high as 1.5 km above the summit and drifted in various directions. The Alert Level remained at Level 2 (on a scale of 1-4) and the public was warned to stay 4 km away from the Malupang Warirang Crater.

Geological summary: The Dukono complex in northern Halmahera is on an edifice with a broad, low profile containing multiple peaks and overlapping craters. Almost 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 Gunung Mamuya cone, 10 km NE. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also had reported eruptions.

Great Sitkin, United States

52.076°N, 176.13°W; Elev. 1,740 m

The Alaska Volcano Observatory (AVO) reported that slow lava effusion continued to feed a thick flow in Great Sitkin’s summit crater during 12-19 August based on webcam and satellite images. The flow advanced mainly E. Minor earthquakes were detected daily, likely associated with rockfalls on the growing dome. Weather clouds often obscured webcam and satellite 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 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 older edifice and produced a submarine debris avalanche. Deposits from this and an even 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. Eruptions have been recorded since the late-19th century.

Ibu, Indonesia

1.4941°N, 127.6324°E; Elev. 1,357 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that activity at Ibu continued during 13-19 August, with daily eruptive events recorded by the seismic network. Gray or white-to-gray ash plumes rose 300-800 m above the summit and drifted in multiple directions, especially towards the N and NE on most days; emissions were not visible on 19 August. The Alert Level remained at 2 (the second lowest level on a four-level scale) and the public was advised to stay 2 km away from the active crater and 3.5 km away from the N crater wall opening.

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.

Kanlaon, Philippines

10.4096°N, 123.13°E; Elev. 2,422 m

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) reported continuing eruptive activity at Kanlaon during 12-18 August. The seismic network recorded 0-7 daily volcanic earthquakes; the counts included 1-3 daily periods of tremor during 14-15 and 17 August, lasting two minutes to one hour and 34 minutes. Sulfur dioxide emissions ranged from 887 to 3,304 tonnes per day. Volcanic emissions rose as high as 200 m above the summit and drifted NNE, ENE, and E. A grayish ash emission lasting 92 minutes on 13 August rose 200 m above the summit and drifted ENE. On 14 August there were five ash emissions and on 15 August there were three ash emissions, each lasting five minutes to just over an hour. One of the 14 August ash emissions, at 0549, was grayish and rose 200 m above the summit and drifted N. On 17 August one ash emission was recorded for 94 minutes. The Alert Level remained at 2 (on a scale of 0-5); the public was warned to stay out of the 4-km-radius Permanent Danger Zone (PDZ) and pilots were advised to avoid flying close to the summit.

Geological summary: Kanlaon volcano (also spelled Canlaon) forms the highest point on the Philippine island of Negros. The massive andesitic stratovolcano is covered with fissure-controlled pyroclastic cones and craters, many of which are filled by lakes. The largest debris avalanche known in the Philippines traveled 33 km SW from Kanlaon. The summit contains a 2-km-wide, elongated northern caldera with a crater lake and a smaller but higher active vent, Lugud crater, to the south. Eruptions recorded since 1866 have typically consisted of phreatic explosions of small-to-moderate size that produce minor local ashfall.

Kilauea, United States

19.421°N, 155.287°W; Elev. 1,222 m

The Hawaiian Volcano Observatory (HVO) reported that the eruption within Kilauea’s Kaluapele summit caldera, characterized by episodic fountaining, incandescence, and intermittent spatter from craters along the SW margin of Halema`uma`u Crater, continued at variable levels during 13-18 August. The 53rd episode of lava fountaining began at 1545 on 12 August and ended at 0123 on 13 August, after 9.6 hours of continuous activity. The average effusion rate was 135 cubic meters per second; the highest peak was 230 cubic meters per second, occurring at around 1715. An estimated 6 million cubic meters of lava erupted and covered 40-50 percent of the Halema`uma`u Crater floor. The S vent did not produce a fountain, but instead emitted flames. Large lava overflows occurred at the S vent at 1526 and 1538, each lasting approximately 5-6 minutes. A small flow occurred at the W vent (previously referred to as a new collapse feature) at 1531 and lasted for 28 minutes, ending 14 minutes after the start of the fountaining episode. Two more flows, from the S vent and the W vent, began at 1602 and 1603, respectively. The flow from the S vent only lasted three minutes. In contrast, the flow at the W vent lasted 14 minutes and intensified until it finally overflowed and drained into the S vent.

Weak-to-moderate intermittent incandescence at the N vent was observed during 13-14 and 17-18 August, while the S vent appeared dark. A few weak flashes of glow occurred at the W vent during 17-18 August. During most of the week weather conditions from Hurricane Lala obscured views. The Volcano Alert Level remained at Advisory (the second lowest level on a four-level scale) and the Aviation Color Code remained at Yellow (the second lowest color on a four-color scale).

Geological summary: Kilauea overlaps the E flank of the massive Mauna Loa shield volcano in the Island of Hawai`i. 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 Halema`uma`u 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, Indonesia

8.542°S, 122.775°E; Elev. 1,703 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that eruptive activity continued at Lewotobi Laki-Laki during 13-18 August. Multiple daily gray ash plumes rose 200-1,000 m above the summit and drifted NW, W, and SW. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 5 km away from the center of Laki-Laki.

Geological summary: The Lewotobi edifice in eastern Flores Island is composed of the two adjacent Lewotobi Laki-laki and Lewotobi Perempuan stratovolcanoes (the “husband and wife”). Their summits are less than 2 km apart along a NW-SE line. The conical Laki-laki to the NW has been frequently active during the 19th and 20th centuries, while the taller and broader Perempuan has had observed eruptions in 1921 and 1935. Small lava domes have grown during the 20th century in both of the summit craters, which are open to the north. A prominent cone, Iliwokar, occurs on the E flank of Perampuan.

Lewotolok, Indonesia

8.274°S, 123.508°E; Elev. 1,431 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported increasing eruptive activity at Lewotolok during 13-19 August. White plumes rose as high as 500 m above the summit and drifted in multiple directions. Incandescent material was ejected above the summit and onto the flanks daily, as far as 400 m S and 500 m SE. Ash plumes rose 500 m above the summit and drifted SW at 1317 on 15 August and rose 400 m above the summit and drifted W at 1900 that same day. Real-time Seismic Amplitude Measurements (RSAM) data showed a sharp increase on 16 August. White-and-gray plumes rose as high as 500 m on 17 August. Observers reported that during the morning of 18 August lava had flowed over the crater rim and traveled 400 m down the S flank. The flow had advanced through the day and by the evening was 1.2 km long. The Alert Level remained at 2 (on a scale of 1-4). The public was warned to stay 2 km away from the summit, but on 19 August the exclusion zone was expanded to 3 km on the S and SE flanks.

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, Philippines

13.257°N, 123.685°E; Elev. 2,462 m

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) reported that the eruption at Mayon continued at low levels during 12-17 August. Each day the seismic network recorded 4-11 volcanic earthquakes; one rockfall was recorded each day on 15 and 18 August. An ash emission was visible on 12 August. Sulfur dioxide emissions (SO₂) averaged 1,857-3,2957 tonnes per day (t/d) over this reporting period, but increased on 17 August to 8,393 t/d, well above the average of 2,532 t/d recorded since 5 August. The abrupt rise followed recent inflation of the N and E flanks recorded by electronic tilt deformation stations. Emissions declined to an average of 6,878 t/d on 18 August. The Alert Level remained at 2 (on a 0-5 scale) and the public was 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 periods of andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic density currents 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, Indonesia

7.54°S, 110.446°E; Elev. 2,910 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that the eruption at Merapi (on Java) continued during 13-20 August with lava avalanches produced by the active lava dome on the upper SW flank. The seismic network recorded as many as nine lava avalanches per day that traveled as far as 1.9 km down the Sat/Putih and Krasak, drainages on the SW flank. 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.

Nyamulagira, DR Congo

1.408°S, 29.2°E; Elev. 3,058 m

The eruption at Nyamulagira continued during July and August based on satellite data. Incandescence on the floor of the summit caldera was visible in multiple partly or mostly cloudy satellite images. Active lava flows on the NNW and NW flanks, near the crater rim, were identified in a 20 July image and an active flow on the SW flank was visible in a 9 August image. The active parts of the flows were apparent in a beautifully clear 14 August image. Hot spots on the NNW flow were located as far as 700 m from the crater rim, a few hotspots on the NW flow were around 460 m from the crater rim, and the SW flow was mostly hot and about 2.8 km long.

Geological summary: Africa’s most active volcano, Nyamulagira (also known as Nyamuragira), is a massive high-potassium basaltic shield about 25 km N of Lake Kivu and 13 km NNW of the steep-sided Nyiragongo volcano. The summit is truncated by a small 2 x 2.3 km caldera that has walls up to about 100 m high. Documented eruptions have occurred within the summit caldera, as well as from the numerous flank fissures and cinder cones. A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption. Recent lava flows extend down the flanks more than 30 km from the summit as far as Lake Kivu; extensive lava flows from this volcano have covered 1,500 km2 of the western branch of the East African Rift.

Rincon de la Vieja, Costa Rica

10.8314°N, 85.3364°W; Elev. 1,729 m

The Observatorio Vulcanológico y Sismológico de Costa Rica-Universidad Nacional (OVSICORI-UNA) reported that small phreatic eruptions at Rincón de la Vieja were recorded by the seismic and infrasound networks at 1516 on 13 August and at 1050 on 19 August, but not visually observed. A possible small phreatic eruption was recorded at 2220 on 13 August. The Alert Level remained at 3 (Caution) and the Aviation Color Code remained Orange.

Geological summary: Rincón de la Vieja is a volcanic complex in the Guanacaste Range of NW Costa Rica. Sometimes referred to as the Rincon de la Vieja-Santa María Volcanic Complex, it consists of a slightly arcuate 20-km-long ridge of 12 craters and pyroclastic cones constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the “Colossus of Guanacaste,” it has an estimated volume of 130 km3 and contains at least nine major eruptive centers. The Santa María cone, the highest peak of the complex, is located on the E side of the ridge and has a lake within the 400-m-diameter crater. A Plinian eruption producing the 0.25 km3 Río Blanca tephra about 3,500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous reported eruptions possibly dating back to the 16th century, have been from the active crater, near the center of the complex, with an acidic 300-m-diameter lake.

Sabancaya, Peru

15.787°S, 71.857°W; Elev. 5,960 m

The Instituto Geofísico del Perú’s (IGP) Centro Vulcanológico Nacional (CENVUL) reported continuing eruptive activity at Sabancaya during 10-16 August. The seismic network detected 41 seismic events associated with the movement of magmatic fluids, along with earthquakes indicating internal rock fracturing; no volcanic explosions occurred during the period. Gas, steam, and ash emissions periodically rose as high as 600 m above the summit and drifted less than 10 km E and SE. Moderate sulfur dioxide (SO₂) emissions averaged 838 tonnes per day, and seven thermal anomalies (each 1 MW or less) associated with the lava dome were identified. The Alert Level remained at Orange (the third level on a four-color scale) and the public was warned to stay outside of a 12 km radius from the summit.

Geological summary: Sabancaya, located in the saddle NE of Ampato and SE of Hualca Hualca volcanoes, is the youngest of these volcanic centers and the only one to have erupted in historical time. The oldest of the three, Nevado Hualca Hualca, is of probable late-Pliocene to early Pleistocene age. The name Sabancaya (meaning “tongue of fire” in the Quechua language) first appeared in records in 1595 CE, suggesting activity prior to that date. Holocene activity has consisted of Plinian eruptions followed by emission of voluminous andesitic and dacitic lava flows, which form an extensive apron around the volcano on all sides but the south. Records of observed eruptions date back to 1750 CE.

Semeru, Indonesia

8.108°S, 112.922°E; Elev. 3,657 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that activity continued at Semeru during 13-19 August, with daily eruptive events recorded by the seismic network. Daily white-to-gray or gray ash plumes rose 300-1,200 m above the summit and drifted multiple directions. The Alert Level remained at 3 (the second lowest level on a scale of 1-4) and the public was warned to stay at least 5 km away from the Jonggring Saloko Crater in all directions, 13 km from the summit on the SE flank along the Kobokan drainage, and 500 m from the banks of the Kobokan drainage as far as 17 km SE of the summit.

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.

References:

¹ Smithsonian Institution / US Geological Survey Weekly Volcanic Activity Report – GVP – August 13-19, 2026 – Managing Editor: Sally Sennert