The Weekly Volcanic Activity Report: June 28 - July 4, 2023

New activity/unrest was reported for 8 volcanoes from June 28 to July 4, 2023. During the same period, ongoing activity was reported for 15 volcanoes.

New activity/unrest

Fagradalsfjall, Iceland

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

Icelandic Meteorological Office (IMO) reported that inflation began in April in the western Reykjanes Peninsula, reaching a total of 3 cm, with rates up to about 1 cm per month. Data possibly indicated accumulating magma at 15 km depth beneath Fagradalsfjall. In June more than 1,000 earthquakes were recorded with most of them located beneath Reykjanestá, NE of Fagradalsfjall and SW of Kleifarvatn.

Seismicity intensified during 3-4 July. An earthquake swarm began at 1400 on 4 July and more than 1,600 earthquakes were detected beneath Fagradalsfjall, in the vicinity of the July 2022 dike intrusion, by mid-morning on 5 July. The earthquake locations became shallower within the first few hours of the swarm and by 5 July were at depths of 2-3 km. Seven of the earthquakes were above M 4, with the largest being M 4.6 recorded at 0821 on 5 July. At 1055 on 5 July IMO raised the Aviation Color Code to 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.

Klyuchevskoy, Central Kamchatka (Russia)

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

KVERT reported that a minor Strombolian eruption that began at Klyuchevskoy on 22 June continued through 29 June. A daily thermal anomaly was identified in satellite images. 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.

Kuchinoerabujima, Ryukyu Islands (Japan)

30.443°N, 130.217°E | Summit elev. 657 m

The number of shallow volcanic earthquakes gradually increased at Kuchinoerabujima, with a total of 100 events recorded during 17-26 June, prompting JMA to raise the Alert Level to 2 (on a scale of 1-5). During late on 26 June until 1834 on 27 June a total of 50 shallow volcanic earthquakes were recorded, an increased rate of events. At 1930 JMA raised the Alert Level to 3. Earthquakes continued to be recorded during the rest of the week; there were 41, 18, 9, and 9 events respectively recorded each day during 27-30 June, with most epicenters located near Furudake Crater, and some near Shindake Crater (just N of Furudake). Sulfur dioxide emissions remained at low levels and no changes were visible to the gas-and-steam emissions which rose as high as 100 m above the crater rim. No obvious changes at the geothermal area near the fissure on the W side of the Shindake were visible during daily field surveys during 28 June-1 July; weather clouds obscured views during 29-30 June. SAR radar data from 30 June revealed inflation within an area extending several hundred meters around the Furudake crater. The public was warned that ejected blocks and pyroclastic flows may impact areas within 2 km of Shindake.

Geological summary: A group of young stratovolcanoes forms the eastern end of the irregularly shaped island of Kuchinoerabujima in the northern Ryukyu Islands, 15 km W of Yakushima. The Furudake, Shindake, and Noikeyama cones were erupted from south to north, respectively, forming a composite cone with multiple craters. All historical eruptions have occurred from Shindake, although a lava flow from the S flank of Furudake that reached the coast has a very fresh morphology. Frequent explosive eruptions have taken place from Shindake since 1840; the largest of these was in December 1933. Several villages on the 4 x 12 km island are located within a few kilometers of the active crater and have suffered damage from eruptions.

Lokon-Empung, Sulawesi

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

PVMBG reported continuing daily emissions at Lokon-Empung during 28 June-4 July. White plumes with variable densities rose as high as 250 m above the crater rim and drifted S and W on most days. On 2 July white-and-gray plumes rose 100-300 m and drifted N and S. The volcano Alert Level remained at 2 (on a scale of 1-4) and the public was reminded not to approach Tompaluan Crater within a radius of 1.5 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 eruptive activity continued at Mayon during 27 June-4 July. Daily steam-and-gas emissions rose as high as 2.5 km above the crater and drifted multiple directions. Average daily measurements of sulfur dioxide emissions fluctuated between 595 and 1,002 tonnes per day. Slow lava effusion fed the growing dome and flows that advanced down the Mi-Isi (S) and Bonga (SE) drainages. Maximum lava flow lengths along the Mi-Isi drainage extended from 1.6 km on 28 June to 2.7 km by 2 July; the maximum in the Bonga drainage was 1.2 km during 27-28 June, reached 1.3 km on 29 June, and remained at that distance through 2 July. The dome remained unstable and produced incandescent rockfalls and pyroclastic density currents (PDCs, or pyroclastic flows) that sent material up to 4 km away from the crater; seismic stations recording 254-397 daily rockfall events and 4-17 daily PDC events (each lasting 2-4 min). An advisory report about increased activity on 30 June noted four dome-collapse PDC events between 1809 and 2000 that traveled 3-4 km down the Basud drainage, each lasted four minutes. Ashfall was reported during 29 June-1 July in Tabaco (about 13 km NW). The Disaster Response Operations Monitoring and Information Center (DROMIC) reported that as of 1800 on 3 July there were 18,717 people displaced from 26 barangays within the province of Albay, and overall 37,944 were affected. The Alert Level remained at 3 (on a 0-5 scale). Residents were reminded to stay away from the 6-km-radius Permanent Danger Zone (PDZ), and 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.

Piton de la Fournaise, Reunion Island (France)

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

OVPF reported that a seismic crisis at Piton de la Fournaise began at 0736 on 2 July and was accompanied by rapid deformation. Volcanic tremor began at 0830, signifying the arrival of magma at the surface, and fissures opened on the E flank. OVPF recommended a change in the Alert Level to 2-1, the lowest of two sub-levels in “Alert 2: ongoing eruption” (inside the Enclos Fouqué caldera); Alert 2 is the third level on a four-color eruption scale. An overflight was conducted, and three fissures were located at an elevation of about 2,000 m in an area N of Piton Vouvoul. Two fissures were near each other, and one was located to the NE; all three trended NE-SW. Lava from the two at the higher elevation traveled ENE and lava from the third fissure traveled E. Tremor decreased sharply and during 1145-1230 no surface activity was visible. Tremor was variable and again increased; a fourth fissure opened at around 1750 at the top of the Grandes Pentes on the SE flank, around 1,500 m elevation. The fissure was about 500 m long, trended NNW-SSE, and produced lava flows that traveled E.

By 0430 on 3 July the SE flank fissure was the most active of the two fissure areas, with lava flows traveling longer distances to the E than from the higher E-flank fissures. In general, the lava emission rate fluctuated between 7 and 27 meters per second (m/s), averaging 12 m/s, based on satellite data. Field teams made visual observations during 0800-1000 on 3 July and noted that the E-flank fissures were no longer active, producing only gas emissions. The lava flows from those fissures had stopped at around 1,700 m elevation. Active lava fountaining was building several cones along the SE-flank fissure. The lava flows continued to advance, reaching 650 m elevation, in an area about 2.4 km from the nearest road. A sharp decline in volcanic tremor amplitude was noted at 1012 and remained at lower levels. During 3-4 July the lava emission rate fluctuated between 5 and 20 m/s based on satellite data, and the flow front advanced at a rate of about 40 meters per hour based on webcam images. By 1424 on 4 July the lava flow was about 3.5 km long based on satellite image analysis.

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.

Taal, Luzon (Philippines)

14.002°N, 120.993°E | Summit elev. 311 m

PHIVOLCS reported continuing unrest at Taal during 26 June-4 July. Daily white steam-and-gas plumes, voluminous during the first half of the week, rose as high as 2.4 km above the lake and drifted NE, NW, S, and SW; voggy conditions were reported during 2-3 July. Upwelling gasses and hot fluids in the lake were periodically visible. Sulfur dioxide emissions were variable, averaging 7,480 (28 June), 1,165 (30 June), and 4,472 (3 July) tonnes per day. Two periods of volcanic tremor, each lasting 2-3 minutes long, and three volcanic earthquakes were recorded during 26-29 June. There were 9-11 daily volcanic earthquakes recorded during 29 June-2 July, including 1-8 periods of volcanic tremor, each lasting 1-14 minutes. One volcanic earthquake was recorded during 2-3 July. 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 of its most powerful historical eruptions. Though not topographically prominent, its prehistorical eruptions have greatly changed the landscape of SW Luzon. 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, and several eruptive centers lie submerged beneath the lake. 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

IGP and INGEMMET reported that the eruption at Ubinas continued during 26 June-4 July. A thermal anomaly in the crater was detected for the first time on 26 June and continued to be periodically detected through 4 July. According to IGP there were 98 Volcano-tectonic (VT) earthquakes indicating rock fracturing and 52 long-period (LP) earthquakes signifying the movement of gas and magma recorded during 26-28 June. Earthquakes indicting emissions decreased. Ash-and-gas emissions were visible in webcam images rising as high as 1 km above the crater rim and drifting NW, W, and SW. Seismic activity significantly increased during 29-30 June with 173 VT earthquakes, 351 LP events, and harmonic tremor, which signified rising magma. Ash-and-gas plumes rose 800 m and drifted SW, NW, NE, and E. Sulfur dioxide emissions were 600-1,150 tons per day (t/d). The Gobierno Regional de Moquegua raised the Alert Level to Orange (the third level on a four-color scale) on 30 June based on the recommendation from IGP and INGEMMET.

IGP noted that ash emissions were continuously observed in satellite and webcam images during 30 June-1 July and drifted more than 10 km S and SE. During 1-2 July there were 72 VT events and 114 LP events; seismic signals indicating emissions decreased on 2 July. Ash-and-gas plumes rose as high as 1.7 km above the crater rim and drifted SE, S, SW, and NW. Ashfall was reported in Ubinas (6.5 km SSE) and Ouerapi (4.5 km SE). During 2-3 July INGEMMET noted that ash-and-gas plumes rose 400 m and drifted SW, causing ashfall in areas within 5 km downwind. Sulfur dioxide emissions were 700 t/d.

Activity significantly increased on 4 July. IGP counted 16 seismic signals associated with explosive activity. According to INGEMMET an explosion ejected ballistics and produced an ash-and-steam plume that rose 5.5 km and drifted SW and S. Ashfall was recorded in Querapi, Ubinas, Sacohaya (7 km SSE), Anascapa (11 km SE), San Miguel (10 km SE), Tonohaya (7 km SSE), Huatahua, Huarina, Escacha (9 km SE), and Matalaque (17 km SSE), and was most significant within 5 km of the volcano. IGP noted that ash fell within a radius of 20 km and deposits were 1 mm thick in towns in the district of Ubinas.

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.

Ongoing activity

Cotopaxi, Ecuador

0.677°S, 78.436°W | Summit elev. 5911 m

IG reported that moderate eruptive activity continued at Cotopaxi during 27 June-4 July. Seismic stations recorded long-period earthquakes (LPs) and eruption tremors daily; volcano-tectonic earthquakes (VTs) were detected during 27-28 and 30 June and 3-4 July. Snow and ice melted from the summit and triggered small lahars that descended the Agualongo drainage during the afternoons of 27 and 29 June and the NW flank during the afternoon of 1 July. Frequent degassing episodes were observed during 27 June-1 July; weather clouds sometimes obscured views of the summit. Ash plumes were observed in webcam and satellite images and described in aviation notices issued by the Washington VAAC during 2-3 July. The plumes rose 500-1,000 m above the crater and drifted W; ashfall was reported in El Rosal (34 km SW), Ticatilín (15 km WSW), San Agustín del Callo (16 km WSW), San Ramón (16 km WSW), and Rumipamba de Villacís (19 km WSW), all within the parish of Mulaló. The Secretaría de Gestión de Riesgos maintained the Alert Level at Yellow (the second highest level on a four-color scale).

Geological summary: The symmetrical, glacier-covered, Cotopaxi stratovolcano is Ecuador’s most well-known volcano and one of its most active. The steep-sided cone is capped by nested summit craters, the largest of which is about 550 x 800 m in diameter. Deep valleys scoured by lahars radiate from the summit of the andesitic volcano, and large andesitic lava flows extend to its base. The modern edifice has been constructed since a major collapse sometime prior to about 5,000 years ago. Pyroclastic flows (often confused in historical accounts with lava flows) have accompanied many explosive eruptions, and lahars have frequently devastated adjacent valleys. Strong eruptions took place in 1744, 1768, and 1877. Pyroclastic flows descended all sides of the volcano in 1877, and lahars traveled more than 100 km into the Pacific Ocean and western Amazon basin. Smaller eruptions have been frequent since that time.

Fuego, South-Central Guatemala

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

INSIVUMEH reported that 1-3 explosions per hour were recorded at Fuego most days during 27 June-4 July. Explosions generated gas-and-ash plumes that rose as high as 800 m above the crater rim and drifted as far as 30 km SW, W, and NW. The explosions occasionally triggered weak-to-moderate avalanches that descended the Ceniza, Santa Teresa, and Las Lajas ravines. Ashfall was reported each day in areas downwind including Finca Asuncion (12 km SW), El Porvenir (8 km SE), Panimanché I and II (8 km SW), Morelia (9 km SW), Santa Sofía (12 km SW), Yucales (12 km SW), Finca Palo Verde (10 km WSW), Sangre de Cristo (8 km W), Yepocapa (9 km WNW), La Rochela (8 km SSW), and Ceylan (8 km S).

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.

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 27 June-4 July. Periodic radar images confirmed that the flow field expanded to the east within the summit crater. Minor seismicity was ongoing, and a few daily small earthquakes were recorded. Elevated surface temperatures were identified in satellite images during 27-28 June and 1-2 July and minor steaming was visible in satellite and webcam views during 1-3 July; weather clouds sometimes obscured webcam and satellite views on the other days. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level 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 daily dense white gas-and-steam plumes from Karangetang were visible rising as high as 400 m and drifting NE, NW, and W during 28 June-4 July. Periodic webcam images published in the reports showed incandescence at Main Crater (S crater) and from material on the flanks of Main Crater; an image from 1732 on 1 July suggested that a pyroclastic flow descended the SE flank as evident from a linear plume of ash-and-gas rising along its path. Incandescent material extended about 1 km down the S flank and about 600 m down the SSW and SW flanks in a Sentinel satellite image from 2 July. 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.

Kilauea, Hawaiian Islands (USA)

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

On 30 June HVO stated that Kilauea was no longer erupting. Lava supply to the lake ceased on 19 June and sulfur dioxide emissions had decreased to near pre-eruption background levels. Seismicity was also low. The Volcano Alert Level was lowered 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). The report noted that gradual inflation was detected at summit tiltmeters during 19-30 June. Incandescence from previously erupted lava was visible in overnight webcam images during 29-30 June; the lava continued to cool.

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.

Lewotolok, Lembata Island

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

PVMBG reported that the eruption at Lewotolok continued during 28 June-4 July. Emissions mainly consisted of dense white steam-and-gas plumes that rose as high as 800 m above the summit and drifted NW, W, SW, and SE. During 30 June-1 July white-and-gray ash plumes rose 200-700 m above the summit and drifted E, SE, S, and SW. Incandescent material being ejected above the summit was visible in webcam images from 1859 on 29 June, 2227 on 30 June, 0103 on 2 July, and 2339 on 3 July. 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 23-29 June and seismicity remained at elevated levels. The SW lava dome produced 130 lava avalanches that traveled as far as 2 km down the SW flank (upstream in the Boyong drainage) and one that traveled 300 m NW down the Senowo 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.

Popocatepetl, Mexico

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

CENAPRED reported that ongoing activity at Popocatépetl during 27 June-4 July included 29-72 daily steam-and-gas emissions, sometimes containing minor amounts of ash. Seismic activity was characterized as daily periods of high-frequency events and variable amplitude tremors, harmonic tremor, and both minor and moderate explosions. During 27-28 June there were three major and two minor explosions, along with emissions of steam, gas, and ash that rose 1 km above the crater and drifted to the WNW and NW; minor ashfall was reported over that time in Ixtapaluca (42 km NW), Valle de Chalco (44 km NW), and Nezahualcóyotl (54 km NW) in the State of Mexico. Two moderate explosions were recorded during 28-29 June; plumes of steam, gas, and ash rose as high as 1.6 km above the crater and drifted to the W, WNW, and NW, causing minor ashfall in Amecameca de Juárez (18 km NW), Ozumba (18 km W), Temamatla (32 km NW) and moderate ashfall in Tenango del Aire (29 km NW) in the State of Mexico. During 30 June-1 July emissions of steam, gas and ash rose 1 km above the crater and drifted to the NW, and ashfall was reported in Atlautla (16 km W), Chalco and Tlalmanalco (27 km NW), and moderate in Amecameca and Cocotitlan (34 km NW) in the state of Mexico.

Two moderate explosions were again recorded during 1-2 July, and emissions of steam, gas, and ash rose as high as 1.6 km and drifted to the SSW, SW, WSW, and NW. Minor ashfall was reported in Atlautla, Ecatzingo (15 km SW), Yecapixtla (30 km SW), Ocuituco (23 km SW), Tetela del Volcán (18 km SSW), Hueyapan (17 km SW), Cuautla (43 km SW), and Ayala (48 km SW) in the state of Morelos. During 2-3 July emissions of steam, gas, and ash rose 1.3 km above the crater and drifted to the SW and W. The Alert Level remained at Yellow, Phase Two (the middle level on a three-color scale) and the public was warned to stay 12 km away from the crater.

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

Rincon de la Vieja, Costa Rica

10.83°N, 85.324°W | Summit elev. 1916 m

OVSICORI-UNA reported periodic small phreatic events at Rincón de la Vieja during 28 June-4 July. Small phreatic events were recorded at 0156 on 1 July, 0305 on 2 July, and 0229 on 4 July. A more notable event at 0635 on 4 July produced a gas-and-steam plume that rose 700 m above the crater rim and drifted W; the plume was seen by residents in Liberia (21 km SW).

Geological summary: Rincón de la Vieja, the largest volcano in NW Costa Rica, is a remote volcanic complex in the Guanacaste Range. The volcano consists of an elongated, arcuate NW-SE-trending ridge 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. Activity has migrated to the SE, where the youngest-looking craters are located. The twin cone of Santa María volcano, the highest peak of the complex, is located at the eastern end of a smaller, 5-km-wide caldera and has a 500-m-wide 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 historical eruptions possibly dating back to the 16th century, have been from the prominent active crater containing a 500-m-wide acid lake located ENE of Von Seebach crater.

Sangay, Ecuador

2.005°S, 78.341°W | Summit elev. 5286 m

IG reported a high level of eruptive activity at Sangay during 27 June-4 July. Seismic stations recorded 311-923 daily explosions. Crater incandescence was visible in late-night webcam images on 28 June and 2-4 July. Gas, steam, and ash plumes were observed in webcam images or described in aviation notices issued by the Washington VAAC based on satellite images, though weather clouds sometimes prevented views. Emissions rose 0.7-2.1 km above the crater rim and drifted SW, W, and NW during 28-30 June and 2-4 July. Explosions ejected incandescent material that traveled down the SW flank as far as 1.8 km below the crater overnight during 3-4 July. Secretaría de Gestión de Riesgos maintained the Alert Level at Yellow (the second highest level on a four-color scale).

Geological summary: The isolated Sangay volcano, located east of the Andean crest, is the southernmost of Ecuador’s volcanoes and its most active. The steep-sided, glacier-covered, dominantly andesitic volcano grew within the open calderas of two previous edifices which were destroyed by collapse to the east, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. It towers above the tropical jungle on the east side; on the other sides flat plains of ash have been eroded by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of an eruption was in 1628. Almost continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The almost constant activity has caused frequent changes to the morphology of the summit crater complex.

Santa Maria, Southwestern Guatemala

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

INSIVUMEH reported that the eruption at Santa Maria’s Santiaguito lava dome complex continued during 27 June-4 July. Lava dome effusion generated avalanches, pyroclastic density currents (PDC) on all flanks, and fed active lava flows. Daily weak-to-moderate explosions also caused avalanches on all flanks. Explosive activity was highest during 28-29 June with 40 events that produced W- and NW-drifting ash plumes. Almost daily emissions of steam, gas, and sometimes ash rose as high as 1 km above the dome and drifted in multiple directions. Incandescence at the crater and along lava flow margins was visible during most nights and early mornings.

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 the eruption at Semeru continued during 27 June-4 July. During 29-30 June white plumes of variable density rose as high as 100 m above the summit and drifted in multiple directions. Cloudy weather prevented observations during 27-28 June and 1-2 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 eruptive activity continued at Sheveluch during 22-29 June. Daily thermal anomalies were observed in satellite images and intense fumarolic activity was visible from both the active crater and the active lava dome. Aviation notices were issued during 26-27 June due to resuspended ash from the SE flank that sent plumes up to 3 km a.s.l. and drifted as far as 277 km ESE. The Aviation Color Code remained at Orange (the second highest level on a four-color scale). Dates are based on UTC times; specific events are in local time where noted.

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

Stromboli, Aeolian Islands (Italy)

38.789°N, 15.213°E | Summit elev. 924 m

INGV reported that eruptive activity continued at Stromboli during 26 June-2 July. Strombolian activity was observed at summit craters, Area North (Area N) and Area Central-South (Area CS), within the crater terrace, in webcam images. Explosive activity was mainly observed at Area CS (one vent in Sector S1 and three vents in Sector S2). High-pressure degassing sometimes accompanied by the ejection of coarse material was observed at sector S1. An average of 7-9 explosions per hour ejected bombs and lapilli mixed with ash at sector S2. At two vents (one in sector N1 and one in N2) in Area N, an average of 3-5 explosions per hour ejected a mixture of coarse and fine material up to 80 m above the vents. Unstable material detached from an area at the base of crater Area N and triggered moderate landslides that descended the Sciara del Fuoco. The Dipartimento della Protezione Civile maintained the Alert Level at Yellow (the second highest level on a four-level scale).

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

Suwanosejima, Ryukyu Islands (Japan)

29.638°N, 129.714°E | Summit elev. 796 m

JMA reported that minor eruptive activity continued at Suwanosejima’s Ontake crater during 28 June-3 July. Eruptions were recorded during 28-29 June and on 2 July. Ash plumes at 0952 and 1638 on 28 June rose up to 1.2 km above the crater and drifted NE. The next day, at 1232 and 2129 on 29 June, ash plumes rose up to 1 km above the crater and drifted NE. Ash plumes rose to 1.5 km and drifted NE at 2025 on 2 July. 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.

References:

Smithsonian Institution / US Geological Survey Weekly Volcanic Activity Report – June 28 – July 5, 2023 – Managing Editor: Sally Sennert

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