The Weekly Volcanic Activity Report: July 19 – 25, 2023

the weekly volcanic activity report

New activity/unrest was reported for 11 volcanoes. During the same period, ongoing activity was reported for 15 volcanoes.

New activity/unrest: Bagana, Bougainville (Papua New Guinea) | Dempo, Southeastern Sumatra | Fagradalsfjall, Iceland | Langila, New Britain (Papua New Guinea) | Lokon-Empung, Sulawesi | Mayon, Luzon (Philippines) | Nishinoshima, Izu Islands | Piton de la Fournaise, Reunion Island (France) | Shishaldin, Fox Islands (USA) | Ubinas, Peru | Ulawun, New Britain (Papua New Guinea).

Ongoing activity: Aira, Kyushu (Japan) | Cleveland, Chuginadak Island (USA) | Ebeko, Paramushir Island (Russia) | Great Sitkin, Andreanof Islands (USA) | Kanlaon, Philippines | Karangetang, Sangihe Islands | Klyuchevskoy, Central Kamchatka (Russia) | Krakatau, Sunda Strait | Lewotolok, Lembata Island | Merapi, Central Java | Reventador, Ecuador | Semeru, Eastern Java | Sheveluch, Central Kamchatka (Russia) | Suwanosejima, Ryukyu Islands (Japan) | Whakaari/White Island, North Island (New Zealand).

New activity/unrest

Bagana, Bougainville (Papua New Guinea)

6.137°S, 155.196°E | Summit elev. 1855 m

According to new articles, more than 7,000 people needed temporary accommodations due to the eruption at Bagana, with about 1,000 of those in evacuation shelters. Ashfall was deposited over a broad area, contaminating water supplies, affecting crops, and collapsing some roofs and houses in rural areas. Schools were temporarily shut down. The Alert Level was lowered to Stage 2 (on a four-level scale).

Geological summary: Bagana volcano, occupying a remote portion of central Bougainville Island, is one of Melanesia’s youngest and most active volcanoes. This massive symmetrical cone was largely constructed by an accumulation of viscous andesitic lava flows. The entire edifice could have been constructed in about 300 years at its present rate of lava production. Eruptive activity is frequent and characterized by non-explosive effusion of viscous lava that maintains a small lava dome in the summit crater, although explosive activity occasionally producing pyroclastic flows also occurs. Lava flows form dramatic, freshly preserved tongue-shaped lobes up to 50 m thick with prominent levees that descend the flanks on all sides.

Dempo, Southeastern Sumatra

4.016°S, 103.121°E | Summit elev. 3142 m

PVMBG reported that at 2115 on 25 July an eruption at Dempo produced a white-and-gray ash plume that rose at least 2 km above the summit and drifted S and SW. An eruptive event was recorded at 1547 on 26 July but weather conditions prevented views of the volcano. At 2115 PVMBG issued a Volcano Observatory Notice for Aviation (VONA) stating that activity was increasing. The Alert Level remained at 2 (on a scale of 1-4), and the public were reminded to stay 1 km away from the crater and as far as 2 km on the N flank.

Geological summary: Dempo is a stratovolcano that rises above the Pasumah Plain of SE Sumatra. The andesitic complex has two main peaks, Gunung Dempo and Gunung Marapi, constructed near the SE rim of a 3-km-wide amphitheater open to the north. The high point of the older Gunung Dempo crater rim is slightly lower, and lies at the SE end of the summit complex. The taller Marapi cone was constructed within the older crater. Remnants of seven craters are found at or near the summit, with volcanism migrating WNW over time. The active 750 x 1,100 m active crater cuts the NW side of the Marapi cone and contains a 400-m-wide lake at the far NW end. Eruptions recorded since 1817 have been small-to-moderate explosions that produced local ashfall.

Fagradalsfjall, Iceland

63.895°N, 22.258°W | Summit elev. 250 m

IMO reported that lava continued to erupt from main vent at Fagradalsfjall during 19-26 July with no significant changes. Lava from the main vent, which was about 90 x 40 m, continued to advance SSW and sulfur dioxide plumes rose 1-2 km above the crater rim. Seismicity had decreased since the onset of the eruption and was concentrated at the N end of the dike and to the E of Keilir. The lava effusion rate averaged 8 cubic meters per second during 18-23 July based on calculations from the University of Iceland, the Icelandic Institute of Natural History, and the National Land Survey of Iceland. They also estimated that the total erupted volume was about 12.4 million cubic meters, and the flow field covered an area of about 1.2 square kilometers. According to a news article part of the N crater rim collapsed just before noon on 24 July, sending lava flows along a new channel, still mainly to the S but spreading more E. The hiking trails were no longer accessible 24 hours a day and were going to be closed at 1800 each day. Firefighters continued to control the burning vegetation set on fire by the lava. The Aviation Color Code remained at Orange (the third level on a four-color scale).

Geological summary: Although the Fagradalsfjall fissure swarm has previously been considered a split or secondary swarm of the Krýsuvík–Trölladyngja volcanic system, as of September 2022 Icelandic volcanologists managing the Catalogue of Icelandic Volcanoes made the decision to identify it as a distinct separate system. The recent eruptions and related reports have been reassigned here, and other content will be prepared and adjusted as appropriate.

Langila, New Britain (Papua New Guinea)

5.525°S, 148.42°E | Summit elev. 1330 m

The Darwin VAAC reported that ash plumes at Langila were visible in satellite images on 19 July rising 1.8-2.4 km (6,000-8,000 ft) a.s.l. and drifting SE.

Geological summary: Langila, one of the most active volcanoes of New Britain, consists of a group of four small overlapping composite basaltic-andesitic cones on the lower E flank of the extinct Talawe volcano in the Cape Gloucester area of NW New Britain. A rectangular, 2.5-km-long crater is breached widely to the SE; Langila was constructed NE of the breached crater of Talawe. An extensive lava field reaches the coast on the N and NE sides of Langila. Frequent mild-to-moderate explosive eruptions, sometimes accompanied by lava flows, have been recorded since the 19th century from three active craters at the summit. The youngest and smallest crater (no. 3 crater) was formed in 1960 and has a diameter of 150 m.

Lokon-Empung, Sulawesi

1.358°N, 124.792°E | Summit elev. 1580 m

PVMBG reported continuing daily steam-and-gas emissions at Lokon-Empung during 19-25 July. White plumes with variable densities rose as high as 250 m above the crater rim and drifted W and N. The Alert Level remained at 3 (on a scale of 1-4) and the public was reminded not to approach Tompaluan Crater within a radius of 2.5 km.

Geological summary: The Lokong-Empung volcanic complex, rising above the plain of Tondano in North Sulawesi, includes four peaks and an active crater. Lokon, the highest peak, has a flat craterless top. The morphologically younger Empung cone 2 km NE has a 400-m-wide, 150-m-deep crater that erupted last in the 18th century. A ridge extending 3 km WNW from Lokon includes the Tatawiran and Tetempangan peaks. All eruptions since 1829 have originated from Tompaluan, a 150 x 250 m crater in the saddle between Lokon and Empung. These eruptions have primarily produced small-to-moderate ash plumes that sometimes damaged croplands and houses, but lava-dome growth and pyroclastic flows have also occurred.

Mayon, Luzon (Philippines)

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

PHIVOLCS reported that the eruption at Mayon continued during 19-25 July, with slow lava effusion from the summit crater feeding lava flows on the S, SE, and E flanks. The length of the lava flow in the Mi-Isi (S) drainage remained at 2.8 km and the flow in the Bonga (SE) drainage advanced to 2.8 km by 23 July. The lava flow in the Basud drainage on the E flank did not advance, remaining 600 m long. Collapses at the lava dome and from the lava flows produced incandescent rockfalls and pyroclastic density currents (PDCs, or pyroclastic flows) that descended the Mi-Isi, Bonga, and Basud drainages as far as 4 km. Seismicity was dominated by weak low-frequency volcanic earthquakes (LFVQs) originating from a shallow source and were associated with a rapid release of volcanic gases from the summit crater. Some of the events produced audible thunder-like sounds and short dark ash plumes that drifted SW. Between 1733 on 18 July and 0434 on 19 July there were 30 of these events (called “ashing” by PHIVOLCS) recorded by seismic, infrasound, and visual and thermal monitors; each lasted 20-40 seconds long and generated ash plumes that rose 150-300 m above the summit. Sulfur dioxide emissions were reported on most days; variable amounts averaged between 1,581 and 3,135 tonnes per day, with the highest value recorded on 24 July. Each day seismic stations recorded 137-175 rockfall events, 3-4 PDC events, and 5-304 LFVQs. During 19-20 the network recorded three ashing events. At 1956 on 21 July a short-lived (28 seconds) ejection of lava was accompanied by seismic and infrasound signals. The Disaster Response Operations Monitoring and Information Center (DROMIC) reported that as of 1800 on 24 July there were 5,372 families, or 18,782 individuals, that were either in evacuation shelters or staying in other types of alternative housing. 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.

Nishinoshima, Izu Islands

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

The Tokyo VAAC reported that an ash plume from Nishinoshima was seen by a pilot and identified in a satellite image at 0630 on 21 July drifting S at an altitude of 3 km (10,000 ft) a.s.l.

Geological summary: The small island of Nishinoshima was enlarged when several new islands coalesced during an eruption in 1973-74. Another eruption that began offshore in 2013 completely covered the previous exposed surface and enlarged the island again. Water discoloration has been observed on several occasions since. The island is the summit of a massive submarine volcano that has prominent satellitic 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.

Piton de la Fournaise, Reunion Island (France)

21.244°S, 55.708°E | Summit elev. 2632 m

OVPF reported that the eruption that began on 2 July at Piton de la Fournaise was ongoing during 19-25 July, though weather conditions often obscured views. The active cone was about 30 m tall and located on the upper part of Grandes Pentes, SE of Enclos Fouqué, at approximately 1,720 m a.s.l. Volcano-tectonic earthquake events fluctuated throughout the week but remained low relative to the onset of the eruption. The lava lake in the cone was low and lava was occasionally ejected above the rim. Lava was mainly transported through lava tubes and was not visible immediately near the cone. The longest part of the flow did not advance and remained stalled 1.8 km from the road, but the flow field continued to widen and thicken. Breakouts were visible in areas between 1,300 m and 1,500 m elevation. The total volume of lava effused since the beginning of the eruption was an estimated 8.5 +/- 3 million cubic meters by 22 July.

Geological summary: Piton de la Fournaise is a massive basaltic shield volcano on the French island of Réunion in the western Indian Ocean. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three scarps formed at about 250,000, 65,000, and less than 5,000 years ago by progressive eastward slumping, leaving caldera-sized embayments open to the E and SE. Numerous pyroclastic cones are present on the floor of the scarps and their outer flanks. Most recorded eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest scarp, which is about 9 km wide and about 13 km from the western wall to the ocean on the E side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures outside the scarps.

Shishaldin, Fox Islands (USA)

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

AVO reported that the effusive and explosive eruption at Shishaldin was continuing during 18-25 July. Satellite images acquired on 18 July, after a period of activity where ash plumes rose to 9.1 km (30,000 ft) a.s.l., showed ash deposits extending to the SW as well as to the SSE where they reached the shore of Unimak Island. Pyroclastic flow deposits up to 3 km long were visible on the N, E, and S flanks, and deposits from lahars triggered by those events extended farther down the flanks. Weather clouds often obscured webcam and satellite views of the summit during 19-21 July, though elevated surface temperatures consistent with low-level eruptive activity in the summit crater were visible in some clear images. Seismicity was low and no infrasound signals indicating explosive activity were detected.

Elevated surface temperatures detected in satellite images overnight during 21-22 July, despite weather cloud cover, were consistent with increased lava effusion. Sulfur dioxide emissions were detected in satellite data midday on 22 July. In a special notice issued at 1653 on 22 July AVO noted that eruptive activity had intensified over the previous six hours, characterized by a steady increase in seismic tremor and intermittent infrasound signals consistent with small explosions. Pilots first reported low-level ash plumes at around 1900. By 2330 the ash plume had risen to 9 km (30,000 ft) a.s.l. based on additional pilot reports and satellite images. The Aviation Color Code was raised to Red (the highest color on a four-color scale) and the Volcano Alert Level was raised to Warning (the highest level on a four-level scale) at 2343. Ash emissions were sustained for just over an hour (from 2320 on 22 July to 0030 on 23 July) and rose as high as 11 km (36,100 ft) a.s.l.; by the end of the period ash plume altitudes had declined to 4.6 km (15,000 ft) a.s.l. Seismic tremor peaked at 0030 on 23 July and then began to rapidly decline at 0109. Activity had significantly declined, and tremor levels were low, by 0418; AVO lowered the Volcano Alert Level to Watch and the Aviation Color Code to Orange. The ash plume had detached and was drifting NE along the Alaska Peninsula. Bursts of increased seismicity were detected by the seismic network throughout the morning but overall remained at low levels. Elevated surface temperatures were identified in satellite images until about 0600. During 23-24 July pilots reported seeing vigorous steam-and-gas plumes rising to about 3 km (10,000 ft) a.s.l.; the plumes may have contained minor amounts of ash. Seismicity was low.

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.

Ubinas, Peru

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

Instituto Geofísico del Perú (IGP) and Instituto Geológico Minero y Metalúrgico (INGEMMET) reported that the eruption at Ubinas continued during 19-25 July. According to IGP there were 46 volcano-tectonic earthquakes indicating rock fracturing and 122 long-period earthquakes signifying the movement of gas and magma recorded by the seismic network during 17-23 July. In addition, there were seven seismic signals associated with major explosive events, and 9-14 hours of seismic signals related to ash emissions.

Both IGP and INGEMMET reported a few notable explosions and ash plumes during the week. At 0530 on 20 July an explosion produced an ash plume that rose 3-4.5 km above the crater rim and drifted W and SW. Another explosion the next day, at 0922 on 21 July, produced an ash-and-gas plume that rose 5 km above the crater rim. Ashfall was reported in Querapi (4.5 km SE), Ubinas (6.5 km SSE), Tonohaya (7 km SSE), Anascapa (11 km SE), Sacohaya, San Miguel (10 km SE), Escacha, Huatagua (14 km SE), Huarina, Escacha (9 km SE), Matalaque (17 km SSE), Logén, Santa Lucía de Salinas, and Salinas de Moche. An explosion at 1323 on 22 July generated an ash plume that rose 5.5 km 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.

Ulawun, New Britain (Papua New Guinea)

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

RVO reported that minor ash emissions at Ulawun began on 18 July, and during the morning of 19 July brown-to-gray emissions with low ash content were rising a few hundred meters above the crater rim and drifting SE. During 20-25 July steam-and-gas plumes with minor-to-moderate amounts of ash rose from the summit crater and rapidly dispersed. The emissions drifted in various directions, but mainly NW; minor ashfall was reported in areas downwind. Sulfur dioxide emissions were detected in satellite images on 21 and 24 July. Seismicity had begun increasing on 16 July, with RSAM values climbing at a slow but erratic rate, and peaking on 18 July. Afterwards RSAM values decreased and remained at low levels (150-200); seismicity was dominated by continuous volcanic tremors. RSAM values steadily increased to 550 during 0400-1400 on 22 July and fluctuated at moderate levels of 300-350 through 23 July. Values were variable on 24 July between values of 400 to 700. The Alert Level remained at Stage 1 (the lowest level on a four-level scale).

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.

Ongoing activity

Aira, Kyushu (Japan)

31.593°N, 130.657°E | Summit elev. 1117 m

JMA reported ongoing activity at both Minamidake Crater and Showa Crater (Aira Caldera’s Sakurajima volcano) during 16-24 July. Very small eruptive events occasionally occurred at Minamidake and incandescence was observed at night. An eruptive event at Showa on 16 July produced an ash plume that rose 1.2 km above the crater rim and drifted N. An explosion at the same crater at 2314 produced an ash plume that rose 1.8 km above the crater rim and drifted N, and also ejected blocks 300-500 m from the vent. Explosions at 1224 and 1232 on 17 July generated ash plumes that rose 2-2.5 km and drifted N, with blocks ejected 500-800 m from the vent. At 2044 on 17 July an ash plume from an explosion rose 1.2 km and drifted N. Sulfur dioxide emissions were very high, averaging 3,200 tons per day on 20 July. 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 Aira caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim of Aira caldera and built an island that was finally joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4850 years ago, after which eruptions took place at Minamidake. Frequent historical eruptions, recorded since the 8th century, have deposited ash on Kagoshima, one of Kyushu’s largest cities, located across Kagoshima Bay only 8 km from the summit. The largest historical eruption took place during 1471-76.

Cleveland, Chuginadak Island (USA)

52.825°N, 169.944°W | Summit elev. 1730 m

AVO reported that numerous earthquakes at Cleveland have been detected by the local seismic network during the previous week and 37 of the events were large enough to be located. Earthquake hypocenters shallowed from depths of less than 18 km during the beginning to depths less than 6 km by the end of the week. The earthquakes were small, at magnitudes less than 2, but the rate of events was unusual for Cleveland. The seismicity along with elevated surface temperatures at the summit crater frequently identified in satellite images and continued gas-and-steam emissions suggested an increased likelihood of a future eruption. The Volcano Alert Level for Cleveland to Advisory (the second level on a four-level scale) and the Aviation Color Code to Yellow (the second color on a four-color scale) at 1218 on 19 July. Earthquakes continued to be detected (but were too small to be located) during 21-23 July. Weather clouds mostly obscured views of the volcano in satellite and web camera images, though minor steaming from the summit occurred during 23-24 July.

Geological summary: The beautifully symmetrical Mount Cleveland stratovolcano is situated at the western end of the uninhabited Chuginadak Island. It lies SE across Carlisle Pass strait from Carlisle volcano and NE across Chuginadak Pass strait from Herbert volcano. Joined to the rest of Chuginadak Island by a low isthmus, Cleveland is the highest of the Islands of the Four Mountains group and is one of the most active of the Aleutian Islands. The native name, Chuginadak, refers to the Aleut goddess of fire, who was thought to reside on the volcano. Numerous large lava flows descend the steep-sided flanks. It is possible that some 18th-to-19th century eruptions attributed to Carlisle should be ascribed to Cleveland (Miller et al., 1998). In 1944 it produced the only known fatality from an Aleutian eruption. Recent eruptions have been characterized by short-lived explosive ash emissions, at times accompanied by lava fountaining and lava flows down the flanks.

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 13-20 July. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E), explosions during 17-19 July generated ash plumes that rose as high as 4.5 km (14,800 ft) a.s.l and drifted to the NW and SE. Thermal anomalies were identified in satellite images on 17 and 19 July; weather clouds obscured views on other days. 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 continued at Great Sitkin during 19-25 July, producing a thick lava flow in the summit crater. About 10-20 daily local earthquakes were recorded by the seismic network during 19-23 July, and about 20 low-frequency seismic events were detected during 21-22 July. Weather clouds often obscured satellite and webcam views, though a clear image from 19 July showed minor steaming from the lava surface and minimal change to the overall lava flow extent. Minor steaming was again visible in satellite images during 22-24 July. 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.

Kanlaon, Philippines

10.412°N, 123.132°E | Summit elev. 2435 m

PHIVOLCS issued a special notice for Kanlaon at 1000 on 21 July, noting increased seismicity. The seismic network detected 35 volcano-tectonic earthquakes between 2200 on 20 July and 0906 on 21 July at depths of 12-15 km beneath the summit crater. The earthquakes had local magnitudes of 0.9-2.3. Ground deformation data from continuous GPS and electronic tilt data had been recording inflation at the mid-flanks of the volcano since March. Sulfur dioxide emissions at the summit crater averaged 786 tonnes per day (t/d) on 18 July and 230 t/d on 21 July, slightly higher than the average of 566 t/d measured in March. The number of volcano-tectonic earthquakes decreased during the rest of the week; there were 16 recorded during 21-22 July and 1-2 daily earthquakes during 23-25 July. The Alert Level remained at 1 (on a scale of 0-5) and PHIVOLCS reminded the public to remain outside of the 4-km-radius Permanent Danger Zone.

Geological summary: Kanlaon volcano (also spelled Canlaon), the most active of the central Philippines, forms the highest point on the island of Negros. The massive andesitic stratovolcano is dotted 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, historically active vent, Lugud crater, to the south. Historical eruptions, recorded since 1866, have typically consisted of phreatic explosions of small-to-moderate size that produce minor ashfalls near the volcano.

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 rising as high as 100 m and drifting E, NE, NW, and W on most days during 19-25 July. The Darwin VAAC noted that ash plumes rose as high as 2.4 km (8,000 ft) a.s.l. at 1710 on 21 July, at 1530 on 22 July, and at 0850 on 23 July, that drifted NE and E. According to a news source, lava avalanches traveled more than 1.7 km down the Kahetang drainage, 1 km down the Batuawang and Batang drainages, 800 m down the Timbelang drainage, and about 1.5 km down the West Beha drainage during 21-22 July. Dense gray-to-white plumes sometimes accompanied the lava avalanches. 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 minor Strombolian eruption at Klyuchevskoy continued during 13-20 July and a daily bright thermal anomaly was identified in satellite images. A new lava flow was first seen on 19 July advancing down the Apakhonchich drainage on the SE flank. The Aviation Color Code remained at Yellow (the second level on a four-color scale).

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.

Krakatau, Sunda Strait

6.102°S, 105.423°E | Summit elev. 155 m

PVMBG reported that daily white gas-and-steam plumes rose as high as 200 m above Krakatau’s summit during 19-25 July and drifted N, NW, W, and SW. At 0843 on 20 July dense dark gray ash plumes rose 500 m above the summit and drifted NW, followed by similar plumes during 0851-0852 that rose 2 km. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay at least 5 km away from the crater.

Geological summary: The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral 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 Rakata, Danan, and Perbuwatan volcanoes 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 cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.

Lewotolok, Lembata Island

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

PVMBG reported that the eruption at Lewotolok continued during 19-25 July. Daily dense white steam-and-gas plumes rose as high as 500 m above the summit and drifted SE, NW, W, and SW. On 21 July white-and-gray plumes rose as high as 500 m and drifted SW, W, and NW. 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.

Merapi, Central Java

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

BPPTKG reported that the eruption at Merapi (on Java) continued during 14-20 July and seismicity remained at elevated levels. The SW lava dome produced a total of 281 lava avalanches that descended multiple flanks; one avalanche traveled 1 km down the Sat/Putih drainage, two traveled as far as 500 m down the Senowo drainage, eight traveled a maximum distance of 2 km down the SW flank upstream from the Boyong drainage, and 270 traveled as far as 1.8 km down the Bebeng. Morphological changes to the SW lava dome were due to continuing collapses of material. The Darwin VAAC reported that multiple minor ash plumes were identified in satellite images on 19 July rising to 3.7 km (12,000 ft) a.s.l. and drifting S and SW. The emissions were more diffuse towards the end of the day and at 2350 on 19 July and 0600 on 20 July were only visible in webcam images. 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.

Reventador, Ecuador

0.077°S, 77.656°W | Summit elev. 3562 m

IG-EPN reported that the eruption at Reventador was ongoing during 18-25 July. Seismicity was characterized by 16-40 daily explosions, long-period earthquakes, harmonic tremor, and tremor associated with emissions. Weather clouds often hindered visual observations, though crater incandescence was visible on most nights and early mornings, and material was seen descending the flanks. Ash-and-gas plumes rose 400 m above the crater rim and drifted NW on 19 July. Crater incandescence was visible during the night of 20-21 July and incandescent blocks rolled 500 m down the flanks. An explosion at 0804 on 22 July produced a plume with moderate amounts of ash that rose 500 m above the crater rim. An explosion at 0509 on 23 July ejected incandescent material onto the flanks that descended 500 m. Ash emissions on 24 July rose less than 200 m and drifted NW. Incandescent material was ejected as far as 400 m onto the flanks. Servicio Nacional de Gestión de Riesgos y Emergencias (SNGRE) maintained the Alert Level at Orange (the second highest level on a four-color scale).

Geological summary: Volcán El Reventador is the most frequently active of a chain of Ecuadorian volcanoes in the Cordillera Real, well east of the principal volcanic axis. The forested, dominantly andesitic stratovolcano has 4-km-wide avalanche scarp open to the E formed by edifice collapse. A young, unvegetated, cone rises from the amphitheater floor about 1,300 m to a height comparable to the rim. It has been the source of numerous lava flows as well as explosive eruptions visible from Quito, about 90 km ESE. Frequent lahars in this region of heavy rainfall have constructed a debris plain on the eastern floor of the scarp. The largest recorded eruption took place in 2002, producing a 17-km-high eruption column, pyroclastic flows that traveled up to 8 km, and lava flows from summit and flank vents.

Semeru, Eastern Java

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

PVMBG reported that eruptive activity continued at Semeru during 19-25 July. White-and-gray ash emissions that were sometimes dense rose as high as 800 m above the summit and drifted in multiple directions during 19-20 and 22-24 July. 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 13-20 July. Intense fumarolic activity was visible at the active dome, and daily thermal anomalies were identified in satellite images. The Aviation Color Code remained at Orange (the third level on a four-color scale). Dates are based on UTC times; specific events are in local time where noted.

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

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 17-24 July. Multiple eruptive events during 19 and 21-24 July produced ash plumes that rose as high as 1.5 km above the crater rim. Some of the plumes drifted N and NW. 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. The Alert Level remained at 2 (on a 5-level scale) and residents were warned to stay 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.

Whakaari/White Island, North Island (New Zealand)

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

On 20 July GeoNet reported that continuing unrest at Whakaari/White Island was characterized by low-level gas-and-steam emissions and decreasing temperatures during the previous month. The temperatures at the large vents declined from 240 degrees Celsius in March to 120 degrees in late June. During an overflight on 18 July steam-and-gas plumes were observed rising from the same vents in the active crater area as previously observed and the discharge rates were relatively unchanged. No evidence of ash emissions or eruptive activity were observed.

After the remaining monitoring instruments on the island failed, observations were made during overflights, from the webcam located on Whakatane, and using satellite data. Significant changes in deformation or sulfur dioxide emissions were not detected in satellite data over the past few months. 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 the Alert Levels reflected the level of unrest at the volcano but also considered the greater level of uncertainty in activity 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.


Smithsonian Institution / US Geological Survey Weekly Volcanic Activity Report – July 19 – 25, 2023 – Managing Editor: Sally Sennert.


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