The Weekly Volcanic Activity Report: August 1 – 7, 2018

New activity/unrest was reported for 5 volcanoes between August 1 and 7, 2018. During the same period, ongoing activity was reported for 10 volcanoes.

New activity/unrest: Ambae, Vanuatu | Etna, Sicily (Italy) | Krakatau, Indonesia | Nevados de Chillan, Chile | Sierra Negra, Isla Isabela (Ecuador).

Ongoing activity: Agung, Bali (Indonesia) | Aira, Kyushu (Japan) | Copahue, Central Chile-Argentina border | Dukono, Halmahera (Indonesia) | Ebeko, Paramushir Island (Russia) | Karymsky, Eastern Kamchatka (Russia) | Kilauea, Hawaiian Islands (USA) | Sabancaya, Peru | Sheveluch, Central Kamchatka (Russia) | Turrialba, Costa Rica.

The Weekly Volcanic Activity Report is a cooperative project between the Smithsonian's Global Volcanism Program and the US Geological Survey's Volcano Hazards Program. Updated by 23:00 UTC every Wednesday, notices of volcanic activity posted are preliminary and subject to change as events are studied in more detail. This is not a comprehensive list of all of Earth's volcanoes erupting during the week. Carefully reviewed, detailed reports on various volcanoes are published monthly in the Bulletin of the Global Volcanism Network.

New activity/unrest

Ambae, Vanuatu

15.389°S, 167.835°E, Elevation 1496 m

According to news articles and the Vanuatu Red Cross, residents of Ambae began to evacuate the island during 1-8 August under the government's orders due to the effects of significant ashfall from the ongoing eruption at Lake Voui. The Red Cross noted that by 8 August over 3,000 people had been moved to Espiritu Santo (W) and Maewo (NE) islands. Video from 3 August showed lahars blocking roads in S Ambae.

Geological summary: The island of Ambae, also known as Aoba, is a massive 2500 km3 basaltic shield that is the most voluminous volcano of the New Hebrides archipelago. A pronounced NE-SW-trending rift zone dotted with scoria cones gives the 16 x 38 km island an elongated form. A broad pyroclastic cone containing three crater lakes (Manaro Ngoru, Voui, and Manaro Lakua) is located at the summit within the youngest of at least two nested calderas, the largest of which is 6 km in diameter. That large central edifice is also called Manaro Voui or Lombenben volcano. Post-caldera explosive eruptions formed the summit craters about 360 years ago. A tuff cone was constructed within Lake Voui (or Vui) about 60 years later. The latest known flank eruption, about 300 years ago, destroyed the population of the Nduindui area near the western coast.

Etna, Sicily (Italy)

37.748°N, 14.999°E, Elevation 3295 m

Based on two field inspections and webcam data, INGV reported that during 30 July-5 August activity at Etna was characterized by gas emissions at the summit craters and Strombolian activity. Three vents at the bottom of the Bocca Nuova crater were active, with gas emissions rising from two vents and sporadic Strombolian activity occurring at a third. Three vents were also active at the bottom of Northeast Crater (NEC); one produced ash emissions, one steam emissions, and Strombolian explosions at the third ejected incandescent material as high as the crater rim. After several months of quiet conditions, explosive activity resumed at the E crater on the E flank of the New Southeast Crater (NSEC). The activity began at 0608 on 1 August with a brownish-gray ash emission that rose several hundred meters above the summit. The event was followed by more ash emissions and then Strombolian activity in the evening.

Geological summary: Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical 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 horseshoe-shaped 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. This volcano is located within the Mount Etna, a UNESCO World Heritage property.

Krakatau, Indonesia

6.102°S, 105.423°E, Elevation 813 m

PVMBG reported that on 2 August multiple events at Anak Krakatau generated ash plumes that rose as high as 300 m above the summit and drifted N. A dense, black ash plume from an event at 1757 rose 200 m and drifted N. During 5-7 August dense gray ash plumes rose 200-600 m above the summit, and summit incandescence was visible at night. The Alert Level remained at 2 (on a scale of 1-4); residents and visitors were warned not to approach the volcano within 1 km of the crater.

Geological summary: The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral Krakatau edifice, perhaps in 416 CE, formed a 7-km-wide caldera. Remnants of this ancestral volcano are preserved in Verlaten and Lang Islands; subsequently Rakata, Danan and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan volcanoes, and left only a remnant of Rakata volcano. This eruption, the 2nd largest in Indonesia during historical time, caused more than 36,000 fatalities, most as a result of devastating tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.

Nevados de Chillan, Chile

36.868°S, 71.378°W, Elevation 3180 m

Servicio Nacional de Geología and Minería (SERNAGEOMIN) Observatorio Volcanológico de Los Andes del Sur (OVDAS) and ONEMI reported continuing activity through 6 August associated with growth of the Gil-Cruz lava dome in Nevados de Chillán’s Nicanor Crater. Seismicity was at moderate-to-high levels, and consisted of long-period events and tremor. The Alert Level remained at Orange, the second highest level on a four-color scale, and residents were reminded not to approach the crater within 3 km. ONEMI maintained an Alert Level Yellow (the middle level on a three-color scale) for the communities of Pinto, Coihueco, and San Fabián.

Geological summary: The compound volcano of Nevados de Chillán is one of the most active of the Central Andes. Three late-Pleistocene to Holocene stratovolcanoes were constructed along a NNW-SSE line within three nested Pleistocene calderas, which produced ignimbrite sheets extending more than 100 km into the Central Depression of Chile. The largest stratovolcano, dominantly andesitic, Cerro Blanco (Volcán Nevado), is located at the NW end of the group. Volcán Viejo (Volcán Chillán), which was the main active vent during the 17th-19th centuries, occupies the SE end. The new Volcán Nuevo lava-dome complex formed between 1906 and 1945 between the two volcanoes and grew to exceed Volcán Viejo in elevation. The Volcán Arrau dome complex was constructed SE of Volcán Nuevo between 1973 and 1986 and eventually exceeded its height.

Sierra Negra, Isla Isabela (Ecuador)

0.83°S, 91.17°W, Elevation 1124 m

IG reported that the eruption at Sierra Negra continued during 1-7 August. Incandescence from active lava flows was visible daily. An increase of tremor began at 2220 on 3 August and lasted two hours, signifying a new pulse of activity on the N flank. Small gas emissions were visible on 4 August, and steam-and-gas emissions were noted on 6 August.

Geological summary: The broad shield volcano of Sierra Negra at the southern end of Isabela Island contains a shallow 7 x 10.5 km caldera that is the largest in the Galápagos Islands. Flank vents abound, including cinder cones and spatter cones concentrated along an ENE-trending rift system and tuff cones along the coast and forming offshore islands. The 1124-m-high volcano is elongated in a NE direction. Although it is the largest of the five major Isabela volcanoes, it has the flattest slopes, averaging less than 5 degrees and diminishing to 2 degrees near the coast. A sinuous 14-km-long, N-S-trending ridge occupies the west part of the caldera floor, which lies only about 100 m below its rim. Volcán de Azufre, the largest fumarolic area in the Galápagos Islands, lies within a graben between this ridge and the west caldera wall. Lava flows from a major eruption in 1979 extend all the way to the north coast from circumferential fissure vents on the upper northern flank. Sierra Negra, along with Cerro Azul and Volcán Wolf, is one of the most active of Isabela Island volcanoes. This volcano is located within the Archipiélago de Colón (Galápagos), a UNESCO World Heritage property.

Ongoing activity

Agung, Bali (Indonesia)

8.343°S, 115.508°E, Elevation 2997 m

PVMBG reported that white plumes rose 100-300 m above Agung’s crater rim during 1 and 2-7 August. The Alert Level remained at 3 (on a scale of 1-4) with the exclusion zone set at a 4-km radius.

Geological summary: Symmetrical Agung stratovolcano, Bali's highest and most sacred mountain, towers over the eastern end of the island. The volcano, whose name means "Paramount," rises above the SE caldera rim of neighboring Batur volcano, and the northern and southern flanks extend to the coast. The summit area extends 1.5 km E-W, with the high point on the W and a steep-walled 800-m-wide crater on the E. The Pawon cone is located low on the SE flank. Only a few eruptions dating back to the early 19th century have been recorded in historical time. The 1963-64 eruption, one of the largest in the 20th century, produced voluminous ashfall along with devastating pyroclastic flows and lahars that caused extensive damage and many fatalities.

Aira, Kyushu (Japan)

31.593°N, 130.657°E, Elevation 1117 m

JMA reported that there were eight events and seven explosions at Minamidake crater (at Aira Caldera’s Sakurajima volcano) during 30 July-6 August, with ashplumes rising as high as 2.5 km above the crater rim and material ejected as far as 700 m. Crater incandescence was seldom visible at night. Sulfur dioxide emissions were very high at 3,200 tons per day on 2 August. The Alert Level remained at 3 (on a 5-level scale).

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.

Copahue, Central Chile-Argentina border

37.856°S, 71.183°W, Elevation 2953 m

According to ONEMI, OVDAS-SERNAGEOMIN reported that during 16-31 July there were 107 volcano-tectonic events recorded at Copahue, and 266 earthquakes indicating fluid movement. Webcams recorded gas-and-ash plumes rising from El Agrio crater as high as 1.5 km and nighttime incandescence. The Alert Level remained at Yellow (second highest level on a four-color scale); SERNAGEOMIN recommended no entry into a restricted area within 1 km of the crater. ONEMI maintained an Alert Level Yellow (the middle level on a three-color scale) for the municipality of Alto Biobío.

Geological summary: Volcán Copahue is an elongated composite cone constructed along the Chile-Argentina border within the 6.5 x 8.5 km wide Trapa-Trapa caldera that formed between 0.6 and 0.4 million years ago near the NW margin of the 20 x 15 km Pliocene Caviahue (Del Agrio) caldera. The eastern summit crater, part of a 2-km-long, ENE-WSW line of nine craters, contains a briny, acidic 300-m-wide crater lake (also referred to as El Agrio or Del Agrio) and displays intense fumarolic activity. Acidic hot springs occur below the eastern outlet of the crater lake, contributing to the acidity of the Río Agrio, and another geothermal zone is located within Caviahue caldera about 7 km NE of the summit. Infrequent mild-to-moderate explosive eruptions have been recorded at Copahue since the 18th century. Twentieth-century eruptions from the crater lake have ejected pyroclastic rocks and chilled liquid sulfur fragments.

Dukono, Halmahera (Indonesia)

1.693°N, 127.894°E, Elevation 1229 m

Based on satellite data, wind model data, and notices from PVMBG, the Darwin VAAC reported that during 1 and 3-7 August ash plumes from Dukono rose to altitudes of 1.8-2.1 km (6,000-7,000 ft) a.s.l. and drifted N and NE.

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.

Ebeko, Paramushir Island (Russia)

50.686°N, 156.014°E, Elevation 1103 m

Volcanologists in Severo-Kurilsk (Paramushir Island), about 7 km E of Ebeko, observed explosions during 29-31 July and on 1 August that sent ash plumes as high as 6 km (19,700 ft) a.s.l. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

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.

Karymsky, Eastern Kamchatka (Russia)

54.049°N, 159.443°E, Elevation 1513 m

KVERT reported that a thermal anomaly over Karymsky was identified in satellite images during 27-29 and 31 July, as well as ash plumes drifting 200 km SE, E, and NE during 28-31 July. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

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.

Kilauea, Hawaiian Islands (USA)

19.421°N, 155.287°W, Elevation 1222 m

HVO reported that the eruption at Kilauea’s Lower East Rift Zone (LERZ) and within Halema`uma`u Crater continued during 1-2 August, with lava flowing through the channel and into the ocean producing laze at several points along a broad 2-km-wide flow front at Ahalanui. A few spillovers from the channel set vegetation on fire. By 3 August the lava-flow velocity in the channel was low and on 4 August the output at Fissure 8 had waned. Part of the flow field shifted W about 250 m; the westernmost edge was about 70 m NE of the boat ramp in Isaac Hale Park by 5 August. The lava channel was completely crusted over by 6 August, and a lava lake bubbled in the Fissure 8 cone. The laze plumes at the ocean entry were greatly diminished. During 7-8 August the lava lake in Fissure 8 was 5-10 m below the spillway into the channel. A decreasing number of small active ooze outs near the coast were visible. 

A collapse event at the summit was recorded at 1155 on 2 August. Seismicity increased afterwards as has been typical since early on in the LERZ eruption, but then decreased along with the rate of deformation. By 7 August deformation had almost stopped. The quiet conditions at the summit represented a significant change from the pattern of seismicity and deformation detected over the past several months.

Geological summary: Kilauea, which overlaps the E flank of the massive Mauna Loa shield volcano, has been Hawaii's most active volcano during historical time. Eruptions are prominent in Polynesian legends; written documentation extending back to only 1820 records frequent summit and flank lava flow eruptions that were interspersed with periods of long-term lava lake activity that lasted until 1924 at Halemaumau crater, within the summit caldera. The 3 x 5 km caldera was formed in several stages about 1500 years ago and during the 18th century; eruptions have also originated from the lengthy East and SW rift zones, which extend to the sea on both sides of the volcano. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1100 years old; 70% of the volcano's surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 km2, destroying nearly 200 houses and adding new coastline to the island.

Sabancaya, Peru

15.787°S, 71.857°W, Elevation 5960 m

Observatorio Vulcanológico del Sur del IGP (OVS-IGP) and Observatorio Vulcanológico del INGEMMET (OVI) reported that explosions at Sabancaya averaged 19 per day during 30 July-5 August. Hybrid earthquakes were infrequent and low magnitude. Gas-and-ash plumes rose as high as 2.6 km above the crater rim and drifted 30 km SE, E, and NE. On 2 August the sulfur dioxide gas flux was high at 5,000 tons/day. The report noted that the public should not approach the crater within 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.

Sheveluch, Central Kamchatka (Russia)

56.653°N, 161.36°E, Elevation 3283 m

KVERT reported that satellite images showed a thermal anomaly over Sheveluch during 27-29 July and 1-2 August. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

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.

Turrialba, Costa Rica

10.025°N, 83.767°W, Elevation 3340 m

OVSICORI-UNA reported that during 2-4 August activity at Turrialba was characterized by sporadic, passive gas-and-ash emissions. Events at 0023 and 0700 on 2 August generated diffuse ash plumes that rose 1 km and 300 m, respectively, and drifted W. An event at 1600 on 4 August produced a diffuse ash plume that rose 300 m.

Geological summary: Turrialba, the easternmost of Costa Rica's Holocene volcanoes, is a large vegetated basaltic-to-dacitic stratovolcano located across a broad saddle NE of Irazú volcano overlooking the city of Cartago. The massive edifice covers an area of 500 km2. Three well-defined craters occur at the upper SW end of a broad 800 x 2200 m summit depression that is breached to the NE. Most activity originated from the summit vent complex, but two pyroclastic cones are located on the SW flank. Five major explosive eruptions have occurred during the past 3500 years. A series of explosive eruptions during the 19th century were sometimes accompanied by pyroclastic flows. Fumarolic activity continues at the central and SW summit craters.

Source: GVP