The Weekly Volcanic Activity Report: April 6 – 12, 2022

New activity/unrest was reported for 5 volcanoes from April 6 to 12, 2022. During the same period, ongoing activity was reported for 20 volcanoes.

New activity/unrest: Bezymianny, Central Kamchatka (Russia) | Poas, Costa Rica | Purace, Colombia | Ruapehu, North Island (New Zealand) | Taal Luzon, (Philippines).

Ongoing activity: Aira Kyushu (Japan) | Dukono, Halmahera | Great Sitkin, Andreanof Islands (USA) | Heard, Kerguelen Plateau | Kadovar, Northeast of New Guinea | Karymsky, Eastern Kamchatka (Russia) | Katmai, Alaska | Kilauea, Hawaiian Islands (USA) | Lewotolok, Lembata Island | Merapi, Central Java | Nevado del Ruiz, Colombia | Pavlof, Alaska Peninsula, Alaska | Rincon de la Vieja, Costa Rica | Sabancaya, Peru | Semeru, Eastern Java | Semisopochnoi, Aleutian Islands (USA) | Sheveluch, Central Kamchatka (Russia) | Suwanosejima, Ryukyu Islands (Japan) | Wolf, Isla Isabela (Galapagos) | Yasur, Vanuatu.

New activity/unrest

Bezymianny, Central Kamchatka (Russia)

KVERT reported that a daily thermal anomaly over Bezymianny was visible in satellite images during 2-8 April. Strong fumarolic activity, incandescence at the lava dome, and avalanches were also reported. The Aviation Color Code remained at Yellow (the second lowest level on a four-color scale). Dates are based on UTC times; specific events are in local time where noted.

Geological summary: Prior to its noted 1955-56 eruption, Bezymianny had been considered extinct. The modern volcano, much smaller in size than its massive neighbors Kamen and Kliuchevskoi, was formed about 4700 years ago over a late-Pleistocene lava-dome complex and an ancestral edifice built about 11,000-7000 years ago. Three periods of intensified activity have occurred during the past 3000 years. The latest period, which was preceded by a 1000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large horseshoe-shaped crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater. This volcano is located within the Volcanoes of Kamchatka, a UNESCO World Heritage property.

Poas, Costa Rica

OVSICORI-UNA reported that on 6 April at 0240 a phreatic explosion from a vent called “Orange Fumarola” located in a fumarolic field along the inner N crater wall at Poás generated a plume that rose 500 m above the crater rim. Activity lasted for three minutes. The event caused a small landslide that modified the vent. Some of the material from the landslide was deposited in a narrow strip about 100 m into the Boca A lake. Stirred sediment was visibly moving in convection cells, turning the lake water from green to a uniform milky gray color as the sediment mixed into the water. Subaerial fumarolic vents at the E and S parts of the lake more vigorously emitted gasses following the event and remained at that level at least through 12 April. Convection in the lake also continued. OVSICORI-UNA noted that satellite data acquired the day before the explosion showed a total of 500 tons of sulfur dioxide released from both Poás and Turrialba.

Geological summary: The broad vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the complex stratovolcano extends to the lower N flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, last erupted about 7,500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world’s most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since an eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water. This volcano is located within the Cordillera Volcanica Central, a UNESCO Biosphere Reserve property.

Purace, Colombia

On 29 March Observatorio Vulcanológico y Sismológico de Popayán, Servicio Geologico Colombiano (SGC), reported that the number of earthquakes at Puracé had increased during the previous few weeks, and were characterized by volcano-tectonic (VT) events, indicating rock fracturing, and long-period (LP) and volcanic tremor (TR) events, indicating fluid movement. The number of events notably increased on 28 March, with 479 VT, 183 (LP), and 119 (TR) events in total. The magnitudes of events abruptly increased the next day; the largest event was a M 3.3 recorded at 1214 on 29 March. Two fractures opened on 29 March, each about 40 m long, and produced gas emissions detected by satellite; ash was reported by observers in the area. The fractures were located along Coconucos Volcanic Chain, between Puracé Volcano and Curiquinga Volcano. The Alert Level was raised to Yellow (the second lowest on a four-color scale) on 30 March.

Seismicity continued to be elevated through 4 April. The earthquakes were low magnitude, and located about 800 m SE of Puracé and beneath Curiquinga, at depths of 2 km on average. The number of events signifying fluid movement was increasing. GNSS (Global Navigation Satellite System) geodetic network and DInSAR (Differential Interferometry by Synthetic Aperture Radar) showed inflation on the millimeter scale. Sulfur dioxide and carbon dioxide emissions increased, based on satellite and ground-based sampling data, and a fumarole on the N flank of Puracé intensified and produced a strong sulfur odor.

Significant unrest continued during 5-11 April. The seismic network recorded a total of 2,077 earthquakes, consisting of 248 VT events, 1,759 LP events, 37 low-energy TR events, and 31 hybrid events. Millimeter-scale inflation persisted, and sulfur dioxide emissions averaged 1,800 tonnes per day.

Geological summary: One of the most active volcanoes of Colombia, Puracé consists of an andesitic stratovolcano with a 500-m-wide summit crater that was constructed over a dacitic shield volcano. It lies at the NW end of a volcanic massif opposite Pan de Azúcar stratovolcano, 6 km SE. A NW-SE-trending group of seven cones and craters, Los Coconucos, lies between the two larger edifices. Frequent explosive eruptions in the 19th and 20th centuries have modified the morphology of the summit crater. The largest eruptions occurred in 1849, 1869, and 1885. This volcano is located within the Cinturo Andino, a UNESCO Biosphere Reserve property.

Ruapehu, North Island (New Zealand)

On 12 April GeoNet reported that unrest at Ruapehu had intensified during the previous week, characterized by increased gas emissions, elevated tremor, and increasing crater lake water temperatures. Tremor levels were elevated but had declined from the peak reached during 6-7 April. Higher levels of gas emissions were confirmed during an overflight on 11 April; a peak carbon dioxide value was the second highest ever recorded at Ruapehu. Lake temperatures continued to slowly climb and reached 38 degrees Celsius. The lake water was gray in color and had area of upwelling over the N vents; sulfur slicks on the lake’s surface were visible. GeoNet noted that temperature and modeled heat input to the lake were within typical ranges for a heating cycle, though the elevated tremor levels and gas emissions suggested that magma was interacting with the geothermal system. The Volcanic Alert Level remained at 2 (on a scale from 0-5) and the Aviation Color Code remained at Yellow.

Geological summary: Ruapehu, one of New Zealand’s most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes dating back to about 200,000 years ago. The dominantly andesitic 110 km3 volcanic massif is elongated in a NNE-SSW direction and surrounded by another 100 km3 ring plain of volcaniclastic debris, including the NW-flank Murimoto debris-avalanche deposit. A series of subplinian eruptions took place between about 22,600 and 10,000 years ago, but pyroclastic flows have been infrequent. The broad summait area and flank contain at least six vents active during the Holocene. Frequent mild-to-moderate explosive eruptions have been recorded from the Te Wai ā-Moe (Crater Lake) vent, and tephra characteristics suggest that the crater lake may have formed as recently as 3,000 years ago. Lahars resulting from phreatic eruptions at the summit crater lake are a hazard to a ski area on the upper flanks and lower river valleys. This volcano is located within the Tongariro National Park, a UNESCO World Heritage property.

Taal Luzon, (Philippines)

PHIVOLCS lowered the Alert Level for Taal to 2 (on a scale of 0-5) on 9 April, noting a significant decrease in activity during the previous two weeks. Sulfur dioxide emissions were high during the first three weeks of March, peaking at 21,211 tonnes per day on 16 March, but dropped on 3 April to an average of 240 tonnes per day; the flux again decreased to 103 tonnes per day on 8 April, the lowest number recorded since unrest began in 2021. During 26 March-9 April only 86 small-magnitude and imperceptible volcanic earthquakes had been recorded, and by 31 March background tremor associated with shallow hydrothermal activity had ceased. Electronic tilt monitoring on Taal Volcano Island, continuous Global Positioning System (GPS) data, and InSAR analysis of Sentinel-1 satellite data indicated continuing deflation of Taal, particularly on the SE flank. Diffuse plumes from the lake had also decreased in frequency, though they rose 600-900 m above the surface during 10-12 April. Sulfur dioxide emissions were below instrumental detection limits on 11 April. PHIVOLCS reminded the public that the entire Taal Volcano Island is 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 historical eruptions. The island is composed of coalescing small stratovolcanoes, tuff rings, and scoria cones that have grown about 25% in area during historical time. Powerful pyroclastic flows and surges from historical eruptions have caused many fatalities.

Ongoing activity

Aira Kyushu (Japan)

JMA reported that incandescence at Minamidake Crater (at Aira Caldera’s Sakurajima volcano) was visible at night during 4-11 April. Very small eruptive events were recorded on 6 and 9 April. The Alert Level remained at 3 (on a 5-level scale), and residents were warned to stay 2 km away from the crater.

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.

Dukono, Halmahera

Based on satellite and wind model data, the Darwin VAAC reported that during 7-12 April ash plumes from Dukono rose to 2.1-2.4 km (7,000-8,000 ft) a.s.l. and drifted NE and NW. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to remain outside of the 2-km exclusion zone.

Geological summary: Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia’s most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the north-flank cone of Gunung Mamuya. This complex volcano presents a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also been active during historical time.

Great Sitkin, Andreanof Islands (USA)

AVO reported that slow lava effusion at Great Sitkin continued during 5-12 April and very low seismicity persisted. The lava flows on the S, W, and N flanks had advanced up to 10 m during 2-8 April, and elevated surface temperatures identified in satellite images during 8-10 April indicated continuing effusion. Steaming from the vent and flow field was occasionally identified in satellite images. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

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. This volcano is located within the Aleutian Islands, a UNESCO Biosphere Reserve property.

Heard, Kerguelen Plateau

Satellite images of Heard Island’s Big Ben volcano showed thermal anomalies of varying intensity over Mawson Peak (the summit area) and on the NW flank during the previous month. Weather clouds prevented views of the volcano for 11 of the 14 acquisitions during 11 March-13 April. On 11 March a small thermal anomaly at the peak was visible along with a larger anomaly over a vent or multiple vents about 1 km W; the larger anomaly was elongated NE-SW, suggesting a lava flow. Multiple anomalies in the same areas were visible on 31 March and 13 April.

Geological summary: Heard Island on the Kerguelen Plateau in the southern Indian Ocean consists primarily of the emergent portion of two volcanic structures. The large glacier-covered composite basaltic-to-trachytic cone of Big Ben comprises most of the island, and the smaller Mt. Dixon lies at the NW tip of the island across a narrow isthmus. Little is known about the structure of Big Ben because of its extensive ice cover. The historically active Mawson Peak forms the island’s high point and lies within a 5-6 km wide caldera breached to the SW side of Big Ben. Small satellitic scoria cones are mostly located on the northern coast. Several subglacial eruptions have been reported at this isolated volcano, but observations are infrequent and additional activity may have occurred. This volcano is located within the Heard and McDonald Islands, a UNESCO World Heritage property.

Kadovar, Northeast of New Guinea

Based on satellite and wind model data, the Darwin VAAC reported that on 8 April an ash plume from Kadovar rose to an altitude of 1.5 km (5,000 ft) a.s.l. and drifted SE.

Geological summary: The 2-km-wide island of Kadovar is the emergent summit of a Bismarck Sea stratovolcano of Holocene age. It is part of the Schouten Islands, and lies off the coast of New Guinea, about 25 km N of the mouth of the Sepik River. Prior to an eruption that began in 2018, a lava dome formed the high point of the andesitic volcano, filling an arcuate landslide scarp open to the south; submarine debris-avalanche deposits occur in that direction. Thick lava flows with columnar jointing forms low cliffs along the coast. The youthful island lacks fringing or offshore reefs. A period of heightened thermal phenomena took place in 1976. An eruption began in January 2018 that included lava effusion from vents at the summit and at the E coast.

Karymsky, Eastern Kamchatka (Russia)

KVERT reported that a thermal anomaly over Karymsky was visible in satellite images on 3 and 5-6 April; the volcano was quiet or obscured by clouds on the other days during 1-8 April. 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: Karymsky, the most active volcano of Kamchatka’s eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed during the early Holocene. The caldera cuts the south side of the Pleistocene Dvor volcano and is located outside the north margin of the large mid-Pleistocene Polovinka caldera, which contains the smaller Akademia Nauk and Odnoboky calderas. Most seismicity preceding Karymsky eruptions originated beneath Akademia Nauk caldera, located immediately south. The caldera enclosing Karymsky formed about 7600-7700 radiocarbon years ago; construction of the stratovolcano began about 2000 years later. The latest eruptive period began about 500 years ago, following a 2300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been vulcanian or vulcanian-strombolian with moderate explosive activity and occasional lava flows from the summit crater.

Katmai, Alaska

AVO reported that on 8 April strong winds in the vicinity of Katmai and the Valley of Ten Thousand Smokes blew unconsolidated ash SE towards Kodiak Island at an altitude up to 2.4 km (8,000 ft) a.s.l. The ash was originally deposited during the Novarupta eruption in 1912. The Volcano Alert Level remained at Normal and the Aviation Color Code remained at Green.

Geological summary: Prior to 1912, Mount Katmai was a compound stratovolcano with four NE-SW-trending summits, most of which were truncated by caldera collapse in that year. Two or more large explosive eruptions took place from Mount Katmai during the late Pleistocene. Most of the two overlapping pre-1912 Katmai volcanoes are Pleistocene in age, but Holocene lava flows from a flank vent descend the SE flank of the SW stratovolcano into the Katmai River canyon. Katmai was initially considered to be the source of the Valley of Ten Thousand Smokes ash flow in 1912. However, the 3 x 4 km wide caldera of 1912 is now known to have formed as a result of the voluminous eruption at nearby Novarupta volcano. The steep walled young caldera has a jagged rim that rises 500-1000 m above the caldera floor and contains a 250-m-deep, still-rising lake. Lake waters have covered a small post-collapse lava dome (Horseshoe Island) that was seen on the caldera floor at the time of the initial ascent to the caldera rim in 1916. Post-1912 glaciers have formed on a bench within Katmai caldera.

Kilauea, Hawaiian Islands (USA)

HVO reported that lava effusion from a vent in the lower W wall of Kilauea’s Halemaumau Crater continued at variable rates during 5-12 April. Lava from a vent flowed into the active W part of the lava lake, which comprised about 2.3 percent of the total crater floor’s surface, and onto the crater floor. The surface of the lava lake was active all week, and the height of the lake fluctuated. Numerous ooze outs of lava were visible along the lake’s NW, NE, E, and SE margins; a more substantial ooze-out at the N margin was active during 6-7 April. A small outbreak at the W vent was visible overnight during 8-9 April. Just after 2300 on 10 April a flow emerged from the S side on the vent that covered areas along the southwest and western margins through 12 April. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Geological summary: Kīlauea 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. This volcano is located within the Hawaiian Islands, a UNESCO World Heritage property.

Lewotolok, Lembata Island

The eruption at Lewotolok continued during 5-12 April according to PVMBG. Daily white-and-gray ash plumes with variable densities rose as high as 500 m above the summit and drifted E, NW, and W. Photos posted by PVMBG showed nighttime crater incandescence and incandescent material being ejected. The Alert Level remained at 3 (on a scale of 1-4) and the public was warned to stay 3 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

BPPTKG reported no significant morphological changes at Merapi’s summit lava dome during 1-7 April. Based on photo analyses, the volume of the SW lava dome was 1.7 million cubic meters while the central lava dome was 2.6 million cubic meters. Seismicity remained at high levels. As many as 144 lava avalanches originating from the SW dome traveled a maximum of 2 km down the Bebeng drainage on the SW flank. A single pyroclastic flow traveled 1.5 km down the SW flank. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 3-5 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.

Nevado del Ruiz, Colombia

Servicio Geológico Colombiano’s (SGC) reported that at 1713 on 11 April a seismic signal at Nevado del Ruiz was recorded along with an ash, gas, and steam plume. The plume rose almost 3.3 km above the summit and drifted N, causing minor ashfall around the volcano as reported by Parque Nacional Natural Los Nevados staff. It was also visible in webcam images and from the city of Manizales, 28 km NW. The Alert Level remained at 3 (Yellow; the second lowest level on a four-color scale).

Geological summary: Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America’s deadliest eruption.

Pavlof, Alaska Peninsula, Alaska

AVO reported that the eruption at a vent on Pavlof’s upper E flank was ongoing during 5-12 April, and seismic tremor persisted. Elevated surface temperatures were identified in satellite images almost daily. Possible minor lava effusion was visible in satellite images on 6 April, and a few small explosions were recorded each day during 6-9 April. Low-level ash emissions were visible in webcam and satellite images during 6-7 April, and satellite images captured ash and pyroclastic flow deposits extending at most 1.5 km from the vent and short lava flows on 9 April. Steam emissions from the vent were visible during 8-10 April. The Volcano Alert Level remained at Watch and the Aviation Color Code remained at Orange.

Geological summary: The most active volcano of the Aleutian arc, Pavlof is a 2519-m-high Holocene stratovolcano that was constructed along a line of vents extending NE from the Emmons Lake caldera. Pavlof and its twin volcano to the NE, 2142-m-high Pavlof Sister, form a dramatic pair of symmetrical, glacier-covered stratovolcanoes that tower above Pavlof and Volcano bays. A third cone, Little Pavlof, is a smaller volcano on the SW flank of Pavlof volcano, near the rim of Emmons Lake caldera. Unlike Pavlof Sister, Pavlof has been frequently active in historical time, typically producing Strombolian to Vulcanian explosive eruptions from the summit vents and occasional lava flows. The active vents lie near the summit on the north and east sides. The largest historical eruption took place in 1911, at the end of a 5-year-long eruptive episode, when a fissure opened on the N flank, ejecting large blocks and issuing lava flows.

Rincon de la Vieja, Costa Rica

OVSICORI-UNA reported that a small eruptive event at Rincón de la Vieja was recorded at 0136 on 6 April, though the event was not visible due to poor visibility. Two small phreatic eruptions were recorded on 7 April at 1141 and 1323, based on webcam data. The resulting plumes rose 1,000 m and 500 m above the crater, respectively.

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. This volcano is located within the Area de Conservación Guanacaste, a UNESCO World Heritage property.

Sabancaya, Peru

Instituto Geofísico del Perú (IGP) reported moderate levels of activity at Sabancaya during 4-10 April with a daily average of 52 explosions. Gas-and-ash plumes rose as high as 2.5 km above the summit and drifted E, SE, and S. Three thermal anomalies originating from the lava dome in the summit crater were identified in satellite data. Minor inflation continued to be detected near Hualca Hualca (4 km N). The Alert Level remained at Orange (the second highest level on a four-color scale) and the public were warned to stay outside of a 12-km radius.

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

Semeru, Eastern Java

PVMBG reported that the eruption at Semeru continued during 5-12 April. Ash plumes rose 0.4-1 km above the summit during 6 and 8-12 April and drifted N. NW, and SW. The Alert Level remained at 3 (on a scale of 1-4). The public was warned to stay at least 500 m away from Kobokan drainages within 17 km of the summit, along with other drainages originating on Semeru, 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. This volcano is located within the Bromo Tengger Semeru-Arjuno, a UNESCO Biosphere Reserve property.

Semisopochnoi, Aleutian Islands (USA)

AVO reported that low-level eruptive activity at Semisopochnoi’s North Cerberus cone continued during 6-12 April. Periods of seismic tremor were detected daily and occasional small explosions were recorded on most days in seismic and regional infrasound data. Partly-to-mostly-cloudy webcam views and occasional satellite images showed daily short-lived ash bursts and more continuous steam emissions. Steam plumes drifted as far as 70 km SW during 6-7 April. A low-level steam plume drifted more than 100 km at altitudes less than 1.5 km (5,000 ft) a.s.l. during 7-8 April. A low-level ash plume drifted up to 80 km WNW on 8 April. Local ash deposits were occasionally visible. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Geological summary: Semisopochnoi, the largest subaerial volcano of the western Aleutians, is 20 km wide at sea level and contains an 8-km-wide caldera. It formed as a result of collapse of a low-angle, dominantly basaltic volcano following the eruption of a large volume of dacitic pumice. The high point of the island is Anvil Peak, a double-peaked late-Pleistocene cone that forms much of the island’s northern part. The three-peaked Mount Cerberus was constructed within the caldera during the Holocene. Each of the peaks contains a summit crater; lava flows on the N flank of Cerberus appear younger than those on the south side. Other post-caldera volcanoes include the symmetrical Sugarloaf Peak SSE of the caldera and Lakeshore Cone, a small cinder cone at the edge of Fenner Lake in the NE part of the caldera. Most documented eruptions have originated from Cerberus, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone could have been recently active. This volcano is located within the Aleutian Islands, a UNESCO Biosphere Reserve property.

Sheveluch, Central Kamchatka (Russia)

KVERT reported that a thermal anomaly over Sheveluch was identified in satellite images during 2-8 April. The lava dome continued to grow and strong fumarolic activity, incandescence, and avalanches accompanied this activity. 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 1300 km3 volcano is one of Kamchatka’s largest and most active volcanic structures. 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 dot its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large horseshoe-shaped caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. At least 60 large eruptions have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. 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)

JMA reported that eruptive activity continued to be recorded at Suwanosejima’s Ontake Crater during 4-8 April. Two explosions produced eruption plumes that rose as high as 3.3 km above the crater rim and ejected blocks as far as 500 m from the crater. Ashfall was reported in Toshima village (3.5 km SSW). No eruptive activity was noted during 9-11 April, though emissions rose 700 m. The Alert Level remained at 3 and the public was warned to stay 2 km away from the crater.

Geological summary: The 8-km-long, spindle-shaped 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. Suwanosejima, one of Japan’s most frequently active volcanoes, was in a state of intermittent strombolian activity from Otake, the NE summit crater, that began in 1949 and lasted until 1996, after which periods of inactivity lengthened. The largest historical 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 horseshoe-shaped 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.

Wolf, Isla Isabela (Galapagos)

IG reported that the eruption at Wolf continued during 5-12 April. Minor sulfur dioxide emissions were recorded during 5-6 April. Thermal data captured and mapped on 6 April indicated that lava flows were getting closer to the coast; daily thermal alert counts, as many as around 154, indicated active and advancing lava flows during the rest of the week.

Geological summary: Wolf, the highest volcano of the Galápagos Islands, straddles the equator at the north end of the archipelago’s largest island, Isabela. The 1710-m-high edifice has steeper slopes than most other Isabela volcanoes, reaching angles up to 35 degrees. A 6 x 7 km caldera, at 700 m one of the deepest of the Galápagos Islands, is located at the summit. A prominent bench on the west side of the caldera rises 450 above the caldera floor, much of which is covered by a lava flow erupted in 1982. Radial fissures concentrated along diffuse rift zones extend down the north, NW, and SE flanks, and submarine vents lie beyond the north and NW fissures. Similar unvegetated flows originating from a circumferential chain of spatter and scoria cones on the eastern caldera rim drape the forested flanks to the sea. The proportion of aa lava flows at Volcán Wolf exceeds that of other Galápagos volcanoes. An eruption in in 1797 was the first documented historical eruption in the Galápagos Islands. This volcano is located within the Archipiélago de Colón (Galápagos), a UNESCO World Heritage property.

Yasur, Vanuatu

The Wellington VAAC reported that during 9 and 11-12 April ash-and-steam emissions from Yasur were intermittently visible in webcam and satellite images rising 0.9-1.8 km (3,000-6,000 ft) a.s.l. and drifting SE.

Geological summary: Yasur, the best-known and most frequently visited of the Vanuatu volcanoes, has been in more-or-less continuous Strombolian and Vulcanian activity since Captain Cook observed ash eruptions in 1774. This style of activity may have continued for the past 800 years. Located at the SE tip of Tanna Island, this mostly unvegetated pyroclastic cone has a nearly circular, 400-m-wide summit crater. The active cone is largely contained within the small Yenkahe caldera, and is the youngest of a group of Holocene volcanic centers constructed over the down-dropped NE flank of the Pleistocene Tukosmeru volcano. The Yenkahe horst is located within the Siwi ring fracture, a 4-km-wide, horseshoe-shaped caldera associated with eruption of the andesitic Siwi pyroclastic sequence. Active tectonism along the Yenkahe horst accompanying eruptions has raised Port Resolution harbor more than 20 m during the past century.

Reference:

Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 6 April-12 April 2022 – Managing Editor: Sally Kuhn Sennert