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1. Smithsonian / USGS Weekly Volcanic Activity Report 29 August-4 September
2018
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Date: Wed, 5 Sep 2018 12:13:42 -0700
From: Sean Peters <speter24@xxxxxxx>
Subject: Smithsonian / USGS Weekly Volcanic Activity Report 29 August-4 September 2018
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From: "Kuhn, Sally" <KUHNS@xxxxxx>
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Sally Kuhn Sennert - Weekly Report Editor (kuhns@xxxxxx)
URL: https://volcano.si.edu/reports_weekly.cfm
New Activity/Unrest: Krakatau, Indonesia | Manam, Papua New Guinea |
Veniaminof, United States
Ongoing Activity: Aira, Kyushu (Japan) | Ambae, Vanuatu | Dukono,
Halmahera (Indonesia) | Ebeko, Paramushir Island (Russia) | Fuego,
Guatemala | Karymsky, Eastern Kamchatka (Russia) | Kilauea, Hawaiian
Islands (USA) | Mayon, Luzon (Philippines) | Reventador, Ecuador |
Rincon de la Vieja, Costa Rica | Sabancaya, Peru | Sangay, Ecuador |
Santa Maria, Guatemala | Semeru, Eastern Java (Indonesia) | Sheveluch,
Central Kamchatka (Russia) | Sierra Negra, Isla Isabela (Ecuador) |
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 2300 UTC every Wednesday, notices of
volcanic activity posted on these pages 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, but rather a
summary of activity at volcanoes that meet criteria discussed in detail in
the "Criteria and Disclaimers" section. Carefully reviewed, detailed
reports on various volcanoes are published monthly in the Bulletin of the
Global Volcanism Network.
Note: Many news agencies do not archive the articles they post on the
Internet, and therefore the links to some sources may not be active. To
obtain information about the cited articles that are no longer available on
the Internet contact the source.
New Activity/Unrest
Krakatau | Indonesia | 6.102°S, 105.423°E | Summit elev. 813 m
Based on satellite data, the Darwin VAAC reported that during 29-30 August
and during 3-4 September ash plumes from Anak Krakatau rose to altitudes of
1.2-1.5 km (4,000-5,000 ft) a.s.l. and drifted SW, W, NW, and N. The Alert
Level remained at 2 (on a scale of 1-4); residents and visitors were warned
not to approach the volcano within 2 km of the crater.
Geologic 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.
Sources: Darwin Volcanic Ash Advisory Centre (VAAC) http://www.bom.gov.au/
aviation/volcanic-ash/darwin-va-advisory.shtml;
Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)
http://vsi.esdm.go.id/
Manam | Papua New Guinea | 4.08°S, 145.037°E | Summit elev. 1807 m
RVO reported that during 26 August-3 September white plumes rose from
Manam’s Main and Southern craters. Seismicity was at low levels.
Geologic 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.
Source: Rabaul Volcano Observatory (RVO)
Veniaminof | United States | 56.17°N, 159.38°W | Summit elev. 2507 m
Late on 2 September seismic activity at Veniaminof increased, indicative of
unrest, prompting AVO to raise the Aviation Color Code to Yellow and the
Volcano Alert Level to Advisory. The report noted no other signs of
eruptive activity.
Geologic Summary. Massive Veniaminof volcano, one of the highest and
largest volcanoes on the Alaska Peninsula, is truncated by a steep-walled,
8 x 11 km, glacier-filled caldera that formed around 3700 years ago. The
caldera rim is up to 520 m high on the north, is deeply notched on the west
by Cone Glacier, and is covered by an ice sheet on the south. Post-caldera
vents are located along a NW-SE zone bisecting the caldera that extends 55
km from near the Bering Sea coast, across the caldera, and down the Pacific
flank. Historical eruptions probably all originated from the westernmost
and most prominent of two intra-caldera cones, which rises about 300 m
above the surrounding icefield. The other cone is larger, and has a summit
crater or caldera that may reach 2.5 km in diameter, but is more subdued
and barely rises above the glacier surface.
Source: US Geological Survey Alaska Volcano Observatory (AVO)
https://avo.alaska.edu/
Ongoing Activity
Aira | Kyushu (Japan) | 31.593°N, 130.657°E | Summit elev. 1117 m
JMA reported that there were 14 events and 15 explosions at Minamidake
crater (at Aira Caldera’s Sakurajima volcano) during 27 August-3 September,
with ash plumes rising as high as 2.8 km above the crater rim and material
ejected as far as 1.3 km. Crater incandescence was occasionally visible at
night. The sulfur dioxide emission rate was 1,500 tons/day on 27 August.
The Alert Level remained at 3 (on a 5-level scale).
Geologic 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.
Source: Japan Meteorological Agency (JMA) http://www.jma.go.jp/jma/
Ambae | Vanuatu | 15.389°S, 167.835°E | Summit elev. 1496 m
The Vanuatu Meteorology and Geo-hazards Department reported that at 2015 on
1 September explosions at Ambae’s Lake Voui generated ash plumes that rose
4-11 km above the crater rim. According to the Wellington VAAC the ash
plumes were visible in satellite images rising as high as 10.7 km (35,000
ft) a.s.l. and drifting E; the ash quickly dissipated. Moderate ashfall was
likely produced in areas NE and E. The Alert Level remained at 3 (on a
scale of 0-5).
Geologic 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.
Source: Vanuatu Meteorology and Geo-hazards Department
http://www.geohazards.gov.vu/
Dukono | Halmahera (Indonesia) | 1.693°N, 127.894°E | Summit elev. 1229 m
Based on satellite data, wind model data, and notices from PVMBG, the
Darwin VAAC reported that during 29 August-4 September ash plumes from
Dukono rose to altitudes of 1.8-2.1 km (6,000-7,000 ft) a.s.l. and drifted
N, NE, and E.
Geologic 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.
Source: Darwin Volcanic Ash Advisory Centre (VAAC) http://www.bom.gov.au/
aviation/volcanic-ash/darwin-va-advisory.shtml
Ebeko | Paramushir Island (Russia) | 50.686°N, 156.014°E | Summit elev.
1103 m
Volcanologists in Severo-Kurilsk (Paramushir Island), about 7 km E of
Ebeko, observed explosions during 24-31 August that sent ash plumes to 3-6
km (17,100 ft) a.s.l. A thermal anomaly was visible in satellite data
during 24-25 and 30 August. Ash plumes drifted about 135 km SE, S, and SW
during 24-25 and 27-30 August, producing ashfall on 29 and 30 August. The
Aviation Color Code remained at Orange (the second highest level on a
four-color scale).
Geologic 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.
Source: Kamchatkan Volcanic Eruption Response Team (KVERT)
http://www.kscnet.ru/ivs/kvert/index_eng.php
Fuego | Guatemala | 14.473°N, 90.88°W | Summit elev. 3763 m
INSIVUMEH reported that heavy rain generated lahars during 29 August-1
September that descended Fuego’s El Jute (SE), Las Lajas (SE), Cenizas
(SSW), Taniluyá (SW), Seca (W), Mineral, Honda, and Pantaleón (W)
drainages. The lahars were hot, had a sulfur odor, and carried tree
branches and blocks (2-3 m in diameter). On 1 September lahars disrupted
roads between San Pedro Yepocapa (8 km NW) and Sangre de Cristo (8 km WSW),
and from Finca Palo Verde and El Porvenir (8 km ENE). During 2-4 September
explosions produced ash plumes that rose as high as 950 m above the crater
rim and drifted 10-15 km W and SW. Avalanches of incandescent material were
confined to the crater. Ashfall was reported in areas downwind including
San Pedro Yepocapa, Sangre de Cristo, Panimaché I and II (8 km SW), Morelia
(9 km SW), and Finca Palo Verde.
Geologic 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.
Source: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e
Hidrologia (INSIVUMEH) http://www.insivumeh.gob.gt/
Karymsky | Eastern Kamchatka (Russia) | 54.049°N, 159.443°E | Summit
elev. 1513 m
KVERT reported that an ash plume from Karymsky was identified in satellite
images drifting about 40 km S on 25 August. The Aviation Color Code
remained at Orange (the second highest level on a four-color scale).
Geologic 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.
Source: Kamchatkan Volcanic Eruption Response Team (KVERT)
http://www.kscnet.ru/ivs/kvert/index_eng.php
Kilauea | Hawaiian Islands (USA) | 19.421°N, 155.287°W | Summit elev.
1222 m
HVO reported a break in visible lava activity at Kilauea’s Fissure 8 during
26-31 August. On 1 September incandescence at Fissure 8 was evident in the
afternoon; spattering from a small area produced lava flows that slowly
covered the 15 x 65 m crater floor by the evening. Lava continued to fill
the Fissure 8 crater on 3 September. The Volcano Alert Level remained at
Watch and the Aviation Color Code remained at Orange.
Geologic 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.
Source: US Geological Survey Hawaiian Volcano Observatory (HVO)
https://volcanoes.usgs.gov/observatories/hvo/
Mayon | Luzon (Philippines) | 13.257°N, 123.685°E | Summit elev. 2462 m
PHIVOLCS reported that at 0653 on 27 August a short-lived degassing event
at Mayon produced a light-brown ash plume that rose 200 m above the summit
rim and drifted NE. During 28 August-3 September white steam plumes rose as
high as 1 km and drifted in multiple directions. Crater incandescence was
visible nightly. The Alert Level remained at 2 (on a 0-5 scale) and
PHIVOLCS reminded residents to stay away from the 6-km-radius Permanent
Danger Zone and the 7-km Extended Danger Zone on the SSW and ENE flanks.
Geologic Summary. Beautifully symmetrical Mayon, which rises above the
Albay Gulf NW of Legazpi City, is the Philippines' most active volcano. The
structurally simple edifice has steep upper slopes averaging 35-40 degrees
that are capped by a small summit crater. Historical eruptions date back to
1616 and 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 devastated populated lowland areas.
A violent eruption in 1814 killed more than 1,200 people and devastated
several towns.
Source: Philippine Institute of Volcanology and Seismology (PHIVOLCS)
http://www.phivolcs.dost.gov.ph/
Reventador | Ecuador | 0.077°S, 77.656°W | Summit elev. 3562 m
During 29 August-3 September IG reported a high level of seismic activity
at Reventador, including explosions, long-period earthquakes, harmonic
tremor, and signals indicating emissions. Steam, gas, and ash plumes rose
as high as 600 m above the crater rim and drifted NE, NW, and W. Crater
incandescence was visible.
Geologic Summary. Reventador is the most frequently active of a chain of
Ecuadorian volcanoes in the Cordillera Real, well east of the principal
volcanic axis. The forested, dominantly andesitic Volcán El Reventador
stratovolcano rises to 3562 m above the jungles of the western Amazon
basin. A 4-km-wide caldera widely breached to the east was formed by
edifice collapse and is partially filled by a young, unvegetated
stratovolcano that rises about 1300 m above the caldera floor to a height
comparable to the caldera rim. It has been the source of numerous lava
flows as well as explosive eruptions that were visible from Quito in
historical time. Frequent lahars in this region of heavy rainfall have
constructed a debris plain on the eastern floor of the caldera. The largest
historical eruption took place in 2002, producing a 17-km-high eruption
column, pyroclastic flows that traveled up to 8 km, and lava flows from
summit and flank vents.
Source: Instituto Geofísico-Escuela Politécnica Nacional (IG)
http://www.igepn.edu.ec/
Rincon de la Vieja | Costa Rica | 10.83°N, 85.324°W | Summit elev. 1916 m
OVSICORI-UNA reported two distinct, two-minute-long eruptions at Rincón de
la Vieja beginning at 0434 and 1305 on 31 August. Weather conditions
prevented webcam views and estimates of plume heights.
Geologic 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 that was 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 1916-m-high 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 3500 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.
Source: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad
Nacional (OVSICORI-UNA) http://www.ovsicori.una.ac.cr/
Sabancaya | Peru | 15.787°S, 71.857°W | Summit elev. 5960 m
Observatorio Vulcanológico del Sur del IGP (OVS-IGP) and Observatorio
Vulcanológico del INGEMMET (OVI) reported that explosions at Sabancaya
averaged 25 per day during 27 August-2 September. Hybrid earthquakes were
infrequent and of low magnitude. Gas-and-ash plumes rose as high as 3 km
above the crater rim and drifted 50 km SE, E, and NE. The MIROVA system
detected six thermal anomalies, and on 2 September the sulfur dioxide gas
flux was high at 3,970 tons/day. The report noted that the public should
not approach the crater within a 12-km radius.
Geologic 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.
Sources: Instituto Geológico Minero y Metalúrgico (INGEMMET)
http://www.ingemmet.gob.pe/;
Instituto Geofísico del Perú (IGP) http://www.igp.gob.pe/
Sangay | Ecuador | 2.005°S, 78.341°W | Summit elev. 5286 m
Based on satellite images and wind model data, the Washington VAAC reported
that during 28 August-3 September ash emissions from Sangay rose to 5.8-6.7
km (19,000-22,000 ft) a.s.l. and drifted over 45 km in multiple directions.
A thermal anomaly was sometimes visible.
Geologic Summary. The isolated Sangay volcano, located east of the Andean
crest, is the southernmost of Ecuador's volcanoes and its most active. The
steep-sided, glacier-covered, dominantly andesitic volcano grew within
horseshoe-shaped calderas of two previous edifices, which were destroyed by
collapse to the east, producing large debris avalanches that reached the
Amazonian lowlands. The modern edifice dates back to at least 14,000 years
ago. It towers above the tropical jungle on the east side; on the other
sides flat plains of ash have been sculpted by heavy rains into
steep-walled canyons up to 600 m deep. The earliest report of a historical
eruption was in 1628. More or less continuous eruptions were reported from
1728 until 1916, and again from 1934 to the present. The almost constant
activity has caused frequent changes to the morphology of the summit crater
complex.
Source: Washington Volcanic Ash Advisory Center (VAAC)
http://www.ssd.noaa.gov/VAAC/messages.html
Santa Maria | Guatemala | 14.757°N, 91.552°W | Summit elev. 3745 m
INSIVUMEH reported that during 1-4 September weak explosions at Santa
María's Santiaguito lava-dome complex generated ash plumes that rose
600-700 m and drifted SW. Avalanches of material descended the SE flanks of
the lava dome. Ashfall was reported to the south in Monte Claro.
Geologic 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.
Source: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e
Hidrologia (INSIVUMEH) http://www.insivumeh.gob.gt/
Semeru | Eastern Java (Indonesia) | 8.108°S, 112.922°E | Summit elev.
3657 m
Based on analysis of satellite images and wind model data, the Darwin VAAC
reported that on 4 September a discrete eruption at Semeru generated an ash
plume that rose to an altitude of 4.3 km (14,000 ft) a.s.l. and drifted W.
Geologic 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.
Source: Darwin Volcanic Ash Advisory Centre (VAAC) http://www.bom.gov.au/
aviation/volcanic-ash/darwin-va-advisory.shtml
Sheveluch | Central Kamchatka (Russia) | 56.653°N, 161.36°E | Summit
elev. 3283 m
KVERT reported that a thermal anomaly over Sheveluch was identified in
satellite data during 25 and 28-30 August; cloudy weather prevented views
of the volcano on the other days during 24-31 August. The Aviation Color
Code remained at Orange (the second highest level on a four-color scale).
Geologic 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.
Source: Kamchatkan Volcanic Eruption Response Team (KVERT)
http://www.kscnet.ru/ivs/kvert/index_eng.php
Sierra Negra | Isla Isabela (Ecuador) | 0.83°S, 91.17°W | Summit elev.
1124 m
IG reported that the eruption at Sierra Negra that began on 26 June was
divided into two main phases. The first and most energetic phase lasted one
day (26 June) and was characterized by the opening of five fissures and
lava flows traveling as far as 7 km from the vents. Lava was only produced
from fissure 4 during the 57-day-long second phase (27 June-23 August),
with lava reaching the sea on 6 July and expanding the coastline. By 25
August the lava flows in total covered an area of 30.6 square kilometers.
Activity continued to decline the last week of August with decreased
seismicity, gas emission, and no surficial activity visible.
Geologic 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.
Source: Instituto Geofísico-Escuela Politécnica Nacional (IG)
http://www.igepn.edu.ec/
Turrialba | Costa Rica | 10.025°N, 83.767°W | Summit elev. 3340 m
OVSICORI-UNA reported that at 1340 on 30 August an event at Turrialba
produced an ash plume that passively rose 200 m above the crater rim and
drifted SW. Gas-and-ash emissions became continuous during 31 August-1
September, with plumes rising 200 m and drifting SW and W.
Geologic 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: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad
Nacional (OVSICORI-UNA) http://www.ovsicori.una.ac.cr/
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End of Volcano Digest - 31 Aug 2018 to 5 Sep 2018 (#2018-94)
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