The Weekly Volcanic Activity Report: July 5 – 11, 2023

the weekly volcanic activity report

New activity/unrest was reported for 12 volcanoes. During the same period, ongoing activity was reported for 11 volcanoes.

New activity/unrest: Bagana, Bougainville (Papua New Guinea) | Eldey, Reykjanes Peninsula | Fagradalsfjall, Iceland | Kirishimayama, Kyushu (Japan) | Klyuchevskoy, Central Kamchatka (Russia) | Kuchinoerabujima, Ryukyu Islands (Japan) | Mayon, Luzon (Philippines) | Nishinoshima, Izu Islands | Piton de la Fournaise, Reunion Island (France) | San Cristobal, Sierra de los Marrabios | Shishaldin, Fox Islands (USA) | Ubinas, Peru.

Ongoing activity: Ebeko, Paramushir Island (Russia) | Etna, Sicily (Italy) | Fuego, South-Central Guatemala | Great Sitkin, Andreanof Islands (USA) | Karangetang, Sangihe Islands | Merapi, Central Java | Popocatepetl, Mexico | Santa Maria, Southwestern Guatemala | Semeru, Eastern Java | Sheveluch, Central Kamchatka (Russia) | Tofua, Tonga Ridge.

New activity/unrest

Bagana, Bougainville (Papua New Guinea)

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

An explosive eruption at Bagana on 7 July send a large ash, gas, and steam plume to high altitudes and caused significant ashfall in local communities. A report issued by the Autonomous Bougainville Government (Torokina District, Education Section) on 10 July noted that significant ash began falling during 2000-2100 on 7 July and covered most areas in the Vuakovi, Gotana (9 km SW), Koromaketo, Laruma and Atsilima villages. By about 2200 on 7 July the eruption plume had reached upper tropospheric altitudes based on satellite images. Sulfur dioxide detections in satellite images from 8 July indicated that the plume, likely a mixture of gases, ice, and ash, had risen to 16-18 km (52,500-59,100 ft) a.s.l., reaching the tropopause. Ashfall reportedly continued until 9 July. The ashfall covered vegetation, destroying bushes and gardens, and contaminated rivers and streams used for washing and drinking water; residents drank from coconuts and used fresh ground water accessible through bamboo pipes.

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.

Eldey, Reykjanes Peninsula

63.733°N, 23°W | Summit elev. 70 m

Icelandic Meteorological Office (IMO) reported that at 2330 on 6 July earthquake activity increased in an area close to Eldey and by 1500 on 7 July the seismic network had detected over 480 events. The earthquakes were located at depths of around 8 km, with several of the events over M 3 and six over M 4; the largest event was a M 4.5 recorded at 0506 on 7 July. Activity that strong had not previously been detected in conjunction with seismic swarms related to magma intrusions in Fagradalsfjall. The Aviation Color Code was raised to Yellow (the second level on a four-color scale). On 11 July IMO noted that seismicity had decreased during the past few days so at 1640 the Aviation Color Code was lowered to Green.

Geological summary: The Eldey volcanic system is located on the northernmost part of the Reykjanes Ridge and is submarine with the exception of Eldey Island and the skerries (small rocky islands) Eldeyjardrangur, Geirfugladrangur, and Geirfuglasker. Maximum water depth within the system is about 250 m. Eldey has been moderately active in Holocene time. Characteristic activity consists of explosive submarine basaltic eruptions. Six small eruptions have been located within this system during the last 1,100 years, the last occurring in 1926 CE.

Fagradalsfjall, Iceland

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

Icelandic Meteorological Office (IMO) reported that a new fissure eruption in the Fagradalsfjall volcanic system began on 10 July after intensifying seismicity over the previous month and inflation that was first noted in April. At 1055 on 5 July IMO raised the Aviation Color Code to Orange (the third level on a four-color scale). By 1330 on 7 July there had been more than 7,000 earthquakes detected in the swarm that began on 3 July. Epicenters were aligned NE-SW between Fagradalsfjall and the Keilir cone, NNE from the 2021 and 2022 eruptions, and mostly concentrated just N of the Litli Hrútur hill. Deformation data (GPS and radar interferometry) showed uplift in the same area, suggesting a magmatic dike intrusion that reached to 1 km depth by early on 6 July. Seismicity decreased during 6-7 July and the rate of deformation slowed, with analysis showing that by 9-10 July the dike had propagated 1 km further NE.

Tremor was detected at 1425 on 10 July and continued to intensify, leading to an eruption at 1640 just NW of Litli-Hrútur. Webcam images showed visible gas emissions and incandescence, but no major ash emissions. IMO raised the Aviation Color Code to Red (the highest level on a four-color scale) at 1707. Flowing lava from a NE-SW fissure that was about 200 m long was confirmed by people present in the area and webcam images; at 1724 the Aviation Color Code was lowered back to Orange. The fissure was mainly located in a depression and bisected the E and NE flanks of Litli Hrútur. Based on observations from drone video the fissure quickly reached about 900 m long according to estimates from Institute of Earth Sciences. Lava fountaining occurred along the fissure, sending lava flows S. Gas-and-steam emissions drifted NW. According to Almannavarnadeild ríkislögreglustjóra, the police closed the area around the eruption to tourists due to the high concentrations of volcanic gases and particulates from burning vegetation.

Tremor levels peaked between 2100 on 10 July and 0000 on 11 July, then steadily declined through 1100. By 1250 on 11 July the intensity of the eruption had noticeably decreased, with fewer active lava fountains. Only one vent with an elongated crater and multiple lava fountains was active by 1635. Gas plumes rose as high as 4 km above the vent. Lava flows mostly traveled SE and flowed into a shallow valley S of Litli-Hrútur. IMO noted that if lava continued to flow S it may come into contact with the 2022 Merardalir lava flow. A 10-km-long trail from the road up to the eruption site was opened to the public.

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.

Kirishimayama, Kyushu (Japan)

31.934°N, 130.862°E | Summit elev. 1700 m

JMA reported that global navigation satellite system (GNSS) data indicated minor inflation beginning in May at shallow depths beneath Ioyama, located on the NW flank of the Karakuni-dake stratovolcano in the Kirishimayama volcano group. Volcanic tremor was recorded at 1650 on 7 July for the first time since 19 June 2018. JMA raised the Alert Level to 2 (on a 5-level scale) at 1715 on 7 July and warned the public to stay 1 km away from Ioyama. A few shallow volcanic earthquakes were recorded during 7-10 July. Weather conditions mostly prevented visual observations of the fumarolic areas near the crater.

Geological summary: Kirishimayama is a large group of more than 20 Quaternary volcanoes located north of Kagoshima Bay. The late-Pleistocene to Holocene dominantly andesitic group consists of stratovolcanoes, pyroclastic cones, maars, and underlying shield volcanoes located over an area of 20 x 30 km. The larger stratovolcanoes are scattered throughout the field, with the centrally located Karakunidake being the highest. Onamiike and Miike, the two largest maars, are located SW of Karakunidake and at its far eastern end, respectively. Holocene eruptions have been concentrated along an E-W line of vents from Miike to Ohachi, and at Shinmoedake to the NE. Frequent small-to-moderate explosive eruptions have been recorded since the 8th century.

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 29 June-6 July. A daily thermal anomaly was identified in satellite images. Small ash plumes were occasionally observed over the crater during 4-6 July. 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

JMA reported that shallow volcanic earthquakes at Kuchinoerabujima had been occurring frequently starting in late June with most epicenters located near Furudake Crater, and some near Shindake Crater (just N of Furudake). Both the number and magnitude of the volcanic earthquakes increased on 9 June and remained elevated through 12 July; there were 151 events on 9 July, 319 on 10 July, 276 on 11 July, and 172 by 1500 on 12 July. The public was previously warned that ejected blocks and pyroclastic flows may affect areas within 2 km of Shindake, and at 1600 on 10 June the public was also warned to stay 2 km away from Furudake. The Alert Level remained at 3 (on a scale of 1-5).

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.

Mayon, Luzon (Philippines)

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

PHIVOLCS reported that eruptive activity continued at Mayon during 5-11 July. Daily steam-and-gas emissions rose as high as 1 km above the crater and drifted in multiple directions. Average daily measurements of sulfur dioxide emissions fluctuated between 721 and 1,621 tonnes per day. Slow lava effusion from the summit crater continued to feed lava flows on the flanks. The length of the lava flow in the Mi-Isi (S) drainage remained at 2.8 km. The flow in the Bonga (SE) drainage advanced 100 m during 10-11 July, with a total length of 1.4 km. The growing lava dome remained unstable and produced incandescent rockfalls and pyroclastic density currents (PDCs, or pyroclastic flows) that descended the Basud (E) drainage as far as 4 km. Seismic stations recorded 216-511 daily rockfall events, 5-39 daily PDC events (from dome and lava front collapse) lasting 1-3 minutes, and 1-109 volcanic earthquakes. Ashfall was reported during 10-11 July in Legazpi City (13 km SSE), and Budiao (8.1 km S), Salvacion (8.6 km S), Daraga (12 km S), and Camalig (11 km SSW), in Albay. The Disaster Response Operations Monitoring and Information Center (DROMIC) reported that as of 1800 on 10 July, the number of displaced persons and total number of overall affected persons from 26 barangays in the province of Albay increased to 20,141 and 38,376, respectively. 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.

Nishinoshima, Izu Islands

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

JMA reported that at around 1300 on 9 July an eruption plume from Nishinoshima rose 1.6 km above the crater and drifted N. Satellite images acquired at 1420 and 2020 on 9 July and 0220 on 10 July showed continuing emissions rising 1.3-1.6 km and drifting NE and N.

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 5-11 July. Though there were multiple active fissures at the start of the eruption, as of 3 July only the SE flank fissure was active, located on the upper part of Grandes Pentes at approximately 1,720 m a.s.l. Volcano-tectonic earthquake events (VTs) fluctuated throughout the week but remained low relative to the onset of the eruption. The amplitude of the volcanic tremor dropped abruptly at 2105 on 4 July following a M 2.3 earthquake directly below Dolomieu Crater, and again on 7 July. Lava ejections continued to build a cone over the active vent throughout the week. During an overflight on 7 July, a team from OVPF-IPGP determined that the lava flow had reached 1.8 km from the road but had not advanced since 5 July. The flow front did not extend any further to the E, but by 7 July active flows were moving through a lava tube. During 10-11 July flows traveled through lava tubes and were active at elevations above 1,300 m. Although clouds often prevented measurements, satellite analysis showed that lava flow rates fluctuated between 1.5 and 24 cubic m/s. The total volume of lava effused since the beginning of the eruption was an estimated 5.5 million cubic m. Deflation of the whole edifice during 3-6 July ended by 8 July, and no significant deformation was observed the rest of the week.

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.

San Cristobal, Sierra de los Marrabios

12.702°N, 87.004°W | Summit elev. 1745 m

SINAPRED reported that on 5 July a small explosion at San Cristóbal produced a moderately-sized ash-and-gas plume. The emissions in photos posted by SINAPRED appeared to be dense and gray, and pyroclastic flows were visible on the upper flanks. According to news articles, a strong sulfur odor was reported in nearby communities along with the fall of ash and larger tephra, most notably in La Grecia (12 km WSW). Fine ash particles in the air ash continued to impact residents the next day. A dark narrow deposit extending about 10 km W from the summit crater was visible in a 9 July Sentinel satellite image.

Geological summary: The San Cristóbal volcanic complex, consisting of five principal volcanic edifices, forms the NW end of the Marrabios Range. The symmetrical 1745-m-high youngest cone, named San Cristóbal (also known as El Viejo), is Nicaragua’s highest volcano and is capped by a 500 x 600 m wide crater. El Chonco, with several flank lava domes, is located 4 km W of San Cristóbal; it and the eroded Moyotepe volcano, 4 km NE of San Cristóbal, are of Pleistocene age. Volcán Casita, containing an elongated summit crater, lies immediately east of San Cristóbal and was the site of a catastrophic landslide and lahar in 1998. The Plio-Pleistocene La Pelona caldera is located at the eastern end of the complex. Historical eruptions from San Cristóbal, consisting of small-to-moderate explosive activity, have been reported since the 16th century. Some other 16th-century eruptions attributed to Casita volcano are uncertain and may pertain to other Marrabios Range volcanoes.

Shishaldin, Fox Islands (USA)

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

AVO reported that intermittent tremor and low-frequency earthquakes recorded at Shishaldin over the past week had gradually become more regular and consistent during 10-11 July. Strongly elevated surface temperatures at the summit were identified in satellite images during 10-11 July. The Volcano Alert Level was raised to Advisory (the second level on a four-level scale) and the Aviation Color Code was raised to Yellow (the second color on a four-color scale) at 1439 on 11 July, but AVO noted that the increased activity may or may not lead to an eruption.

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

IGP and INGEMMET reported that the eruption at Ubinas continued during 5-12 July. According to IGP there were 67 volcano-tectonic earthquakes indicating rock fracturing and 47 long-period earthquakes signifying the movement of gas and magma recorded during 5-9 July. A period of continuous ash-and-gas emissions was visible on 5 July with the plumes drifting more than 10 km SE and E. The Washington VAAC reported that ash plumes and periodic puffs of ash rose 5.5-9.1 km (18,000-30,000 ft) a.s.l. and drifted N and NE. On 6 July explosions recorded at 0747 and 2330 produced ash-and-gas plumes that rose as high as 3.5 km above the crater rim and drifted within 30 km NW, NE, SE, and S. According to the VAAC the explosion at 0747 produced a plume of ash and gas that rose to 9.1 km a.s.l., drifted SW, and gradually dissipated, while a lower-altitude plume at 7.6 km (25,000 ft) a.s.l. drifted NE. Gobierno Regional de Moquegua declared a state of emergency for districts in the Moquegua region, along with Coalaque Chojata, Icuña, Lloque, Matalaque (17 km SE), Ubinas, and Yunga of the General Sánchez Cerro province, to be in effect for 60 days.

On 7 July the VAAC reported that at 0320 an ash plume rose to 7.3 km (24,000 ft) a.s.l. and drifted E. At 0900 and 1520 steam plumes with diffuse ash rose to 6.7 km (22,000 ft) a.s.l. and drifted SE. Diffuse gas emissions were visible in satellite images drifting SE at 2120. Very small ash puffs visible in satellite and webcam images at 0920 and 1520 on 8 July rose as high as 6.4 km (21,000 ft) a.s.l. and drifted SE. INGEMMET reported that during 9-11 July sulfur dioxide emissions were low at 300 tons per day. Gas-and-steam plumes rose 150-400 m and drifted S. 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.

Ongoing activity

Ebeko, Paramushir Island (Russia)

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

KVERT reported that moderate activity at Ebeko was ongoing during 29 June-6 July. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E), explosions on 4 July generated ash plumes that rose as high as 2.2 km (7,200 ft) a.s.l and drifted to the NW. On 4 and 6 July thermal anomalies were observed in satellite images; weather clouds obscured views on other days. 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 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.

Etna, Sicily (Italy)

37.748°N, 14.999°E | Summit elev. 3357 m

INGV reported that during 9-10 July explosive activity at Etna’s SE Crater produced ash emissions that rapidly dispersed near the summit.

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.

Fuego, South-Central Guatemala

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

INSIVUMEH reported that eruptive activity continued at Fuego during 5-11 July. Steam-and-gas emissions rose 300-540 m above the crater rim and drifted SW, W, and NW. Daily counts of weak and sometimes moderate explosions averaged 2-7 per hour. Explosions triggered weak and moderate avalanches that descended the Honda (E), El Jute (ESE), Las Lajas (SE), Trinidad (S), Ceniza (SSW), and Seca (W) ravines. Sometimes explosions were accompanied by ash plumes that rose as high as 1 km above the crater and drifted as far as 20 km SW, W, and NW. Degassing sounds (similar to a jet engine) lasting 1-2 minutes were reported on most days. Minor ashfall was reported in areas downwind, including El Porvenir (8 km SE), Panimaché I (7 km SW), Morelia (9 km SW), Santa Sofía (12 km SW), Panimaché II (8 km WSW), Finca Palo Verde (10 km WSW), Sangre de Cristo (8 km W), and Yepocapa (9 km WNW).

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 5-11 July. Several local earthquakes were recorded daily during 6-11 July. Minor degassing was observed in satellite data on 6 July and in webcam images during 10-11 July. Weather clouds obscured satellite and webcam views on other days. Elevated surface temperatures at the summit were identified in satellite images during 10-11 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.

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 300 m and drifting multiple directions during 5-11 July. Periodic webcam images published in the reports showed incandescence at Main Crater (S crater) and from material on the flanks of Main Crater. PVMBG issued Volcano Observatory Notices for Aviation (VONAs) about eruptive events at 0759 and 0850 on 10 July; images showed what appeared to be pyroclastic flows descending the S flank of Main Crater. 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.

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 eruptive activity continued at Popocatépetl during 5-11 July. Long-period events totaling 25-123 per day were accompanied by steam-and-gas plumes that sometimes contained minor amounts of ash. Seismic activity also included variable-amplitude volcanic tremors (total of 35 hours), harmonic tremor (9.5 hours), explosions, and volcano-tectonic earthquakes (maximum magnitude 1.6 at 0441 on 9 July). Ash plumes identified in webcam and satellite images were described in daily aviation notices issued by the Washington VAAC; some plumes rose as high as 2.2 km above the summit and drifted NE, SW, W, or NW. Minor explosions occurred at 2336 on 4 July, at 1955 on 6 July, at 0911 and 1937 on 7 July, at 1016 on 8 July, and at 0209 and 0335 on 11 July. Moderate explosions were recorded at 0007 on 9 July and at 0816 on 11 July. At 0843 on 10 July the VAAC reported an ash plume that rose 1 km above the summit and drifted as far as 28 km NW. At 0930 on 10 July ashfall was reported in the municipalities of Ayapango (24 km WNW), Tenango del Aire (29 km WNW), Amecameca (19 km NW), and Temamatla (33 km NW), all within the State of México. The VAAC reported that the plume drifted as far as 185 km NW by noon, and the Secretaría de Gestión Integral de Riesgos y Protección Civil (SGIRPC) of the City of México reported ashfall in Milpa Alta (46 km WNW), Xochimilco (56 km WNW), Coyoacán (65 km WNW), Tlalpan (67 km WNW), La Magdalena Contreras (70 km WNW), Álvaro Obregón (72 km WNW), Cuajimalpa (80 km WNW), Tláhuac (49 km NW), and Iztapalapa (59 km NW). On the morning of 11 July ashfall was reported in the municipalities of Ozumba (18 km W) and Juchitepec (30 km WNW) within the State of México. 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.

Santa Maria, Southwestern Guatemala

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

INSIVUMEH reported that eruptive activity continued at Santa Maria’s Santiaguito lava dome complex during 5-11 July. Lava effusion at Caliente dome fed lava flows, and occasionally produced both avalanches and pyroclastic flows that traveled short distances down the S, SW, and W flanks. Daily weak and sometimes moderate explosions ejected ash plumes as high as 900 m above the dome that drifted W and NW, and triggered avalanches down the E, SE, and S flanks. Incandescence was observed at the crater and along lava flow margins 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 eruptive activity continued at Semeru during 5-11 July, though weather conditions prevented summit observations on most days. On 10 July a dense white plumes rose as high as 600 m above the summit and drifted N, NW, W, and SW. However, emergency management agencies Badan Nasional Penanggulangan Bencana (BNPB) and Badan Penanggulangan Bencana Daerah (BPBD) reported that on 7 July continuous heavy rainfall caused flooding and lahars that affected the following locations in the Lumajang Regency: Kloposawit Village and Tumpeng Village in the Candipuro Subdistrict, Sumerwuluh Village, Pronojiwo Village, Jugosari Village, and Sidomulyo Village in the Pronojiwo Subdistrict, and Nguter Village in the Pasirian Subdistrict. Starting at 0010, lahars descended Semeru’s flanks and damaged 13 bridges, 12 homes, over 80 hectares of crops, and affected livestock. As of 2035 on 10 July, a total of 1,294 people had evacuated to 18 shelter locations. 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 29 June-6 July. Daily thermal anomalies were observed in satellite images and intense fumarolic activity was visible from both the active crater and lava dome. An aviation notice on 2 July described a gas-and-steam plume with some ash that rose 3.5 km a.s.l. and drifted 39 km W. Additional aviation notices caused by resuspended ash were issued on 30 June and 1, 4, and 5 July; plumes rose up to 3 km a.s.l. and drifted as far as 95 km ESE, SE, W, and WNW. 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.

Tofua, Tonga Ridge

19.75°S, 175.07°W | Summit elev. 515 m

Tonga Geological Services issued a public notice on 7 July noting the ongoing eruption at Tofua and requesting that the public contact them with any information, including photos and video. Data and observations indicated that the activity was normal and no significant seismic activity nor thermal anomalies were recorded.

Geological summary: The low, forested Tofua Island in the central part of the Tonga Islands group is the emergent summit of a large stratovolcano that was seen in eruption by Captain Cook in 1774. The summit contains a 5-km-wide caldera whose walls drop steeply about 500 m. Three post-caldera cones were constructed at the northern end of a cold fresh-water caldera lake, whose surface lies only 30 m above sea level. The easternmost cone has three craters and produced young basaltic-andesite lava flows, some of which traveled into the caldera lake. The largest and northernmost of the cones, Lofia, has a steep-sided crater that is 70 m wide and 120 m deep and has been the source of historical eruptions, first reported in the 18th century. The fumarolically active crater of Lofia has a flat floor formed by a ponded lava flow.


Smithsonian Institution / US Geological Survey – Weekly Volcanic Activity Report July 5 – 11, 2023
– Managing Editor: Sally Sennert.

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