New activity/unrest was reported for 4 volcanoes between May 3 and 9, 2017. During the same period, ongoing activity was reported for 16 volcanoes.
New activity/unrest: Aira, Kyushu (Japan) | Fuego, Guatemala | Manam, Papua New Guinea | Poas, Costa Rica.
Ongoing activity: Bagana, Bougainville (Papua New Guinea) | Bezymianny, Central Kamchatka (Russia), Dukono, Halmahera (Indonesia) | Ebeko, Paramushir Island (Russia) | Kambalny, Southern Kamchatka (Russia) | Kanlaon, Philippines | Kilauea, Hawaiian Islands (USA) | Klyuchevskoy, Central Kamchatka (Russia) | Nevados de Chillan, Chile | Sabancaya, Peru | San Miguel, El Salvador | Santa Maria, Guatemala | Sheveluch, Central Kamchatka (Russia) | Sinabung, Indonesia | Suwanosejima, Ryukyu Islands (Japan) | Turrialba, Costa Rica.
Aira, Kyushu (Japan)
31.593°N, 130.657°E, Elevation 1117 m
JMA reported that nine events at Showa Crater (at Aira Caldera’s Sakurajima volcano) were detected during 1-8 May. One of the events was explosive, generating an ash plume that rose 4 km above the crater rim and ejecting material 300-500 m from the crater. Ashfall was reported in the cities of Kagoshima (3 km NW), Hioki (25 km WNW), and Ichikikushikino (40 km NW). Nighttime crater incandescence was noted on 2 and 5 May. An event at 1213 on 5 May at Minamidake summit crater produced a plume that rose 500 m above the crater rim. 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.
14.473°N, 90.88°W, Elevation 3763 m
In a special report INSIVUMEH reported that a new phase of activity (the fourth of the year) at Fuego began on 5 May and was the strongest activity recorded since 2012. Strong explosions, sometimes producing shock waves, generated dense ash plumes that rose 1.3 km above the crater and drifted more than 50 km S, SW, and W. Ashfall was reported in many areas downwind, including San Pedro Yepocapa (8 km N), Morelia (9 km SW), Santa Sofía (12 km SW), El Porvenir (8 km ENE), finca Palo Verde, Santa Lucia Cotzumalguapa (23 km SW), Siquinala, San Andrés Osuna, Chuchu, and La Reunión. Lava flows traveled 2 km down the Santa Teresa (W) drainage and 3 km down the Las Lajas drainage. Pyroclastic flows descended the Trinidad (S), Las Lajas (SE), Ceniza (S), and Santa Teresa drainages. Residents of Sangre de Cristo (8 km WSW) were evacuated. Explosions were not reported that next day and the lava flows may have stopped advancing. According to a news article, about 300 people had been evacuated from Panimache (8 km SW). During 7-8 May lower-energy explosions generated ash plumes that rose as high as 750 m above the crater and drifted 8-20 km W and SW. Gases were observed rising from pyroclastic flow deposits in the ravines.
Geological summary: Volcán Fuego, one of Central America's most active volcanoes, is one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between 3763-m-high Fuego and its twin volcano to the north, Acatenango. 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 Acatenango. In contrast to 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.
Manam, Papua New Guinea
4.08°S, 145.037°E, Elevation 1807 m
RVO reported that another phase of Strombolian activity at Manam’s Southern Crater began around 1700 on 4 May when RSAM values increased to 100-150. A sharp increase in values was detected at 0330 on 5 May, though the highest RSAM value (1,400) occurred between 0500 and 0600. RSAM dropped rapidly to 200 by around 0700, and then by 1400 RSAM values were around 50.
Strombolian activity on 5 May was characterized by loud roaring and rumbling, ejected incandescent material, and ash and scoria fall; some phases of very strong activity occurred during 0530-0600. A lava flow traveled down the SW valley and stopped at 600 m elevation. Minor amounts of ash fell in all parts of the island including Warisi (E), Dugulaba (S), and Boda and Baliab (NW). Though weather clouds prevented visual observations of Manam during 6-8 May, activity in general was very low; noises and crater incandescence were absent, and seismicity was lower than it had been for many weeks (RSAM <50). RVO recommended that the Alert Level be lowered to Stage 2.
Geological summary: The 10-km-wide island of Manam, lying 13 km off the northern coast of mainland Papua New Guinea, is one of the country's most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical 1807-m-high basaltic-andesitic stratovolcano to its lower flanks. These "avalanche valleys" channel lava flows and pyroclastic avalanches that have sometimes reached the coast. Five small satellitic centers are located near the island's shoreline on the northern, southern, and western sides. Two summit craters are present; both are active, although most historical eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent historical eruptions, typically of mild-to-moderate scale, have been recorded since 1616. Occasional larger eruptions have produced pyroclastic flows and lava flows that reached flat-lying coastal areas and entered the sea, sometimes impacting populated areas.
Poas, Costa Rica
10.2°N, 84.233°W, Elevation 2708 m
OVSICORI-UNA reported that an eruption at Poás was detected at 1724 on 6 May through poor visibility prevented visual confirmation of the event. During 6-7 May volcano-tectonic and long-period earthquakes were detected, as well as moderate-amplitude tremor.
Geological summary: The broad, well-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, which is one of Costa Rica's most prominent natural landmarks, are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the 2708-m-high complex stratovolcano extends to the lower northern flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, is cold and clear and last erupted about 7500 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 the first historical eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.
Bagana, Bougainville (Papua New Guinea)
6.137°S, 155.196°E, Elevation 1855 m
Based on analyses of satellite imagery and wind data, the Darwin VAAC reported that during 7-9 May ash plumes from Bagana rose to altitudes of 2.1-3 km (7,000-10,000 ft) a.s.l. and drifted over 110 km SE, SSE, and S.
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.
Bezymianny, Central Kamchatka (Russia)
55.972°N, 160.595°E, Elevation 2882 m
KVERT reported gas-and-steam activity at Bezymianny during 28 April-5 May, and a daily thermal anomaly identified in satellite images. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).
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.
Dukono, Halmahera (Indonesia)
1.693°N, 127.894°E, Elevation 1229 m
Based on analyses of satellite imagery, wind model data, and notices from PVMBG, the Darwin VAAC reported that during 3-6 May ash plumes from Dukono rose to altitudes of 2.1-2.4 km (7,000-8,000 ft) a.s.l. and drifted W, E, 90 km ESE, and 185 km 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
KVERT reported that during 28 April-5 May satellite images of Ebeko showed quiet conditions or weather cloud cover. The Aviation Color Code remained at Orange (the second highest level on a four-color scale). Based on satellite observations, the Tokyo VAAC reported that during 8-9 May plumes rose to altitudes of 2.4-2.7 km (8,000-9,000 ft) a.s.l. and drifted S and NE. The cause of the plumes was unclear, and weather clouds hindered observations.
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.
Kambalny, Southern Kamchatka (Russia)
51.306°N, 156.875°E, Elevation 2116 m
On 5 May KVERT reported that conditions at Kambalny were quiet the previous week. The Aviation Color Code was lowered to Yellow.
Geological summary: The southernmost major stratovolcano on the Kamchatka peninsula, Kambalny has a summit crater that is breached to the SE. Five Holocene cinder cones on the W and SE flanks have produced fresh-looking lava flows. Beginning about 6,300 radiocarbon years ago, a series of major collapses of the edifice produced at least three debris-avalanche deposits. The last major eruption took place about 600 years ago, although younger tephra layers have been found, and an eruption was reported in 1767. Active fumarolic areas are found on the flanks of the volcano, which is located south of the massive Pauzhetka volcano-tectonic depression.
10.412°N, 123.132°E, Elevation 2435 m
On 5 May PHIVOLCS reported that since the last phreatic eruption at Kanlaon, which occurred on 15 June 2016, there has been a general decline in activity: seismicity was at baseline levels, no significant deformation had been detected since August 2016, sulfur dioxide emissions were low, and no steaming had been observed since 29 September 2016. The Alert Level was lowered to 0 (on a scale of 0-5), though the public was warned to not enter the 4-km-radius Permanent Danger Zone (PDZ).
Geological summary: Kanlaon volcano (also spelled Canlaon), the most active of the central Philippines, forms the highest point on the island of Negros. The massive 2435-m-high andesitic stratovolcano is dotted with fissure-controlled pyroclastic cones and craters, many of which are filled by lakes. The largest debris avalanche known in the Philippines traveled 33 km to the SW from Kanlaon. The summit of Kanlaon contains a 2-km-wide, elongated northern caldera with a crater lake and a smaller, but higher, historically active vent, Lugud crater, to the south. Historical eruptions from Kanlaon, recorded since 1866, have typically consisted of phreatic explosions of small-to-moderate size that produce minor ashfalls near the volcano.
Kilauea, Hawaiian Islands (USA)
19.421°N, 155.287°W, Elevation 1222 m
During 3-9 May HVO reported that the lava lake continued to rise, fall, and spatter in Kilauea’s Overlook crater. Webcams recorded incandescence from long-active sources within Pu'u 'O'o Crater, from a vent high on the NE flank of the cone, and from a small lava pond in a pit on the W side of the crater. The 61G lava flow, originating from a vent on Pu'u 'O'o Crater's E flank, continued to enter the ocean at Kamokuna adding to the growing delta. Surface lava flows were active above the pali.
Geological summary: Kilauea volcano, which overlaps the east 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 sq km, destroying nearly 200 houses and adding new coastline to the island.
Klyuchevskoy, Central Kamchatka (Russia)
56.056°N, 160.642°E, Elevation 4754 m
KVERT reported that a weak thermal anomaly was identified in satellite images over Klyuchevskoy during 30 April-1 May, and an ash plume drifted about 52 km E on 1 May. The Aviation Color Code remained at Orange (the second highest 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.
Nevados de Chillan, Chile
36.863°S, 71.377°W, Elevation 3212 m
The Buenos Aires VAAC reported that on 3 May a webcam recorded a puff rising from Nevados de Chillán and dissipating rapidly.
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.
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 during 1-7 May explosive activity at Sabancaya increased, with an average of 41 explosions detected per day. The number of long-period and hybrid events also increased. Ash plumes rose as high as 3.5 km above the crater rim and drifted more than 40 km NE and E.
Based on webcam images, satellite views, and seismic data the Buenos Aires VAAC reported that during 3-9 May sporadic gas-and-ash puffs rose to altitudes of 7-8.2 km (23,000-27,000 ft) a.s.l. and drifted SE, E, and NE.
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.
San Miguel, El Salvador
13.434°N, 88.269°W, Elevation 2130 m
SNET reported that during 28 April-5 May RSAM values at San Miguel had decreased and fluctuated between 50 and 173 units (typical background levels average 50 units). Sulfur dioxide flux was also lower, though changing winds may have affected readings.
Geological summary: The symmetrical cone of San Miguel volcano, one of the most active in El Salvador, rises from near sea level to form one of the country's most prominent landmarks. The unvegetated summit of the 2130-m-high volcano rises above slopes draped with coffee plantations. A broad, deep crater complex that has been frequently modified by historical eruptions (recorded since the early 16th century) caps the truncated summit, also known locally as Chaparrastique. Radial fissures on the flanks of the basaltic-andesitic volcano have fed a series of historical lava flows, including several erupted during the 17th-19th centuries that reached beyond the base of the volcano on the north, NE, and SE sides. The SE-flank lava flows are the largest and form broad, sparsely vegetated lava fields crossed by highways and a railroad skirting the base of the volcano. The location of flank vents has migrated higher on the edifice during historical time, and the most recent activity has consisted of minor ash eruptions from the summit crater.
Santa Maria, Guatemala
14.757°N, 91.552°W, Elevation 3745 m
INSIVUMEH reported that 10-12 explosions at Santa María's Santiaguito lava-dome complex were detected by the seismic network during 4-5 May. Beginning at 2145 on 6 May a strong lahar, 30 m wide and 2.5 m deep, descended the Cabello de Ángel drainage, a tributary of the Nimá I river drainage on Santa María’s S flank, carrying branches, tree trunks, and blocks up to 2 m in diameter.
Geological summary: Symmetrical, forest-covered Santa María volcano is one of the most prominent of a chain of large stratovolcanoes that rises dramatically above the Pacific coastal plain of Guatemala. The 3772-m-high stratovolcano has a sharp-topped, conical profile that is cut on the SW flank by a large, 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 westward-younging vents, the most recent of which is Caliente. Dome growth has been accompanied by almost continuous minor explosions, with periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.
Sheveluch, Central Kamchatka (Russia)
56.653°N, 161.36°E, Elevation 3283 m
KVERT reported that during 28 April-5 May lava-dome extrusion onto Sheveluch’s N flank was accompanied by strong fumarolic activity, dome incandescence, ash explosions, and hot avalanches. A thermal anomaly at the dome was identified daily in satellite images. Ash plumes drifted more than 730 km SE, SW, and NW during 27 April-3 May; explosions on 30 April generated ash plumes that rose to an altitude of 9.1 km (30,000 ft) a.s.l. 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 cu km 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.
3.17°N, 98.392°E, Elevation 2460 m
Based on PVMBG observations, webcam and satellite images, and wind data, the Darwin VAAC reported that during 3-9 May ash plumes from Sinabung rose to altitudes of 3-5.5 km (10,000-18,000 ft) a.s.l. and drifted in multiple directions.
Geological summary: Gunung Sinabung is a Pleistocene-to-Holocene stratovolcano with many lava flows on its flanks. The migration of summit vents along a N-S line gives the summit crater complex an elongated form. The youngest crater of this conical andesitic-to-dacitic edifice is at the southern end of the four overlapping summit craters. An unconfirmed eruption was noted in 1881, and solfataric activity was seen at the summit and upper flanks in 1912. No confirmed historical eruptions were recorded prior to explosive eruptions during August-September 2010 that produced ash plumes to 5 km above the summit.
Suwanosejima, Ryukyu Islands (Japan)
29.638°N, 129.714°E, Elevation 796 m
Based on JMA notices and satellite-image analyses, the Tokyo VAAC reported that on 8 May plumes from Suwanosejima rose to altitudes of 1-2.1 km (3,000-7,000 ft) a.s.l. and drifted N and SW.
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 of the volcano 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.
Turrialba, Costa Rica
10.025°N, 83.767°W, Elevation 3340 m
OVSICORI-UNA reported that an event at Turrialba at 1700 on 5 May generated a weak ash plume that rose 500 m above the crater and drifted SW. Two short-amplitude events occurred at 1702 and 1820 though there was no confirmation if they had corresponded to eruptions. During 5-7 May volcano-tectonic and long-period earthquakes were detected, as well as variable-amplitude tremor. At 1250 on 6 May an event produced a plume that rose 300 m and drifted W. Between 1250 and 1730 a passive ash emission rose no higher than 1 km. Another passive ash emission rose about 500 m at 1000 on 7 May and drifted WNW. At 0902 on 9 May an event generated an ash plume that rose 500 m and drifted NW.
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 3340-m-high Turrialba is exceeded in height only by Irazú, covers an area of 500 sq km, and is one of Costa Rica's most voluminous volcanoes. 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.