Details on Volcanic Activity in 2007

KLIUCHEVSKOI Kamchatka Peninsula, Russia 56.06°N, 160.64°E; summit elev. 4,835 m

KVERT reported that seismic activity at Kliuchevskoi was at background levels during 13-20 July. Based on observations of satellite imagery, ash plumes drifted E on 13 July and a thermal anomaly in the crater was noted during 13-20 July. Ash plumes rose to an altitude of 5.5 km (18,000 ft) a.s.l. and drifted SE and E during 13-15 July, according to video and visual observations. Gas-and-steam plumes were observed on 12, 16, and 18 July. The Level of Concern Color Code was lowered from Orange to Yellow due to a decrease in seismicity and an absence of ash plumes during 17-20 July.

Geologic Summary. Kliuchevskoi is Kamchatka's highest and most active volcano. Since its origin about 7,000 years ago, the beautifully symmetrical, 4,835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. More than 100 flank eruptions, mostly on the NE and SE flanks of the conical volcano between 500 m and 3,600 m elevation, have occurred during the past 3,000 years. The morphology of its 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 major explosive and effusive events from flank craters.

LASCAR northern Chile 23.37°S, 67.73°W; summit elev. 5,592 m

Based on pilot reports and satellite image observations, the Buenos Aires VAAC reported that an ash plume from Lascar rose to altitudes of 7.6-9.1 km (25,000-30,000 ft) a.s.l. on 18 July and drifted NE.

Geologic Summary. Lascar is the most active volcano of the northern Chilean Andes. The andesitic-to-dacitic stratovolcano contains six overlapping summit craters and lies 5 km W of an older, higher stratovolcano, Volcán Aguas Calientes. Lascar consists of two major edifices; activity began at the eastern volcano and then shifted to the western cone. The largest eruption of Lascar took place about 26,500 years ago, and following the eruption of the Tumbres scoria flow about 9,000 years ago, activity shifted back to the eastern edifice, where three overlapping craters were formed. Frequent small-to-moderate explosive eruptions have been recorded from Lascar in historical time since the mid-19th century, along with periodic larger eruptions that produced ashfall hundreds of kilometers away from the volcano. The largest historical eruption of Lascar took place in 1993 and produced pyroclastic flows that extended up to 8.5 km NW of the summit.

SANGAY Ecuador 2.03°S, 78.34°W; summit elev. 5,188 m

Based on pilot observations, the Washington VAAC reported that an ash plume from Sangay rose to an altitude of 5.5 km (18,000 ft) a.s.l. and drifted W on 23 July. Ash was not detected on satellite imagery. On 24 July, a diffuse ash plume at an altitude of 5.2 km (17,000 ft) a.s.l. was visible on satellite imagery drifting SW.

Geologic Summary. The isolated Sangay volcano, located E of the Andean crest, is the southernmost of Ecuador's volcanoes, and its most active. It has been in frequent eruption for the past several centuries. The steep-sided, 5,230-m-high glacier-covered volcano grew within horseshoe-shaped calderas of two previous edifices, which were destroyed by collapse to the E, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. Sangay towers above the tropical jungle on the E side; on the other sides flat plains of ash from the volcano have been sculpted by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of an historical eruption was in 1628. More or less continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The more or less constant eruptive activity has caused frequent changes to the morphology of the summit crater complex.

 SHIVELUCH Kamchatka Peninsula, Russia 56.653°N, 161.360°E; summit elev. 3,283 m

KVERT reported that seismic activity at Shiveluch continued above background levels during 13-20 July. Based on seismic interpretation, ash plumes rose to an altitude of 6 km (19,700 ft) a.s.l. during the reporting period. Gas-and-steam plumes with some ash rose to altitudes of 3-4.5 km (9,800-14,800 ft) a.s.l. during 11-15 and 18-19 July. Based on satellite imagery, plumes drifted S and SW during 15-16 July and a large thermal anomaly was detected in the crater during 13-20 July. The Level of Concern Color Code remained at Orange.

Based on information reported from KEMSD, the Tokyo VAAC reported that an eruption plume rose to 5.8 km (19,000 ft) a.s.l. on 24 July. Ash was not identified on satellite imagery.

Geologic Summary. The high, isolated massif of Shiveluch volcano (also spelled Sheveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group and forms one of Kamchatka's largest and most active volcanoes. The currently active Molodoy Shiveluch lava-dome complex was constructed during the Holocene within a large horseshoe-shaped caldera formed by collapse of the massive late-Pleistocene Strary Shiveluch volcano. At least 60 large eruptions of Shiveluch have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. Frequent collapses of lava-dome complexes, most recently in 1964, have produced large debris avalanches whose deposits cover much of the floor of the breached caldera. During the 1990s, intermittent explosive eruptions took place from a new lava dome that began growing in 1980. The largest historical eruptions from Shiveluch occurred in 1854 and 1964.

SOUFRIÈRE HILLS Montserrat, West Indies 16.72°N, 62.18°W; summit elev. 1,052 m

MVO reported that during 13-24 July, the lava dome at Soufrière Hills changed very little, based on visual observations. Seismic activity was very low and low-level rockfall activity continued. Heavy rainfall generated lahars in E drainages on 19 July. The Alert Level remained elevated at 4 (on a scale of 0-5).

Geologic Summary. The complex dominantly andesitic Soufrière Hills volcano occupies the southern half of the island of Montserrat. The summit area consists primarily of a series of lava domes emplaced along an ESE-trending zone. English's Crater, a 1-km-wide crater breached widely to the E, was formed during an eruption about 4,000 years ago in which the summit collapsed, producing a large submarine debris avalanche. Block-and-ash flow and surge deposits associated with dome growth predominate in flank deposits at Soufrière Hills. Non-eruptive seismic swarms occurred at 30-year intervals in the 20th century, but with the exception of a 17th-century eruption that produced the Castle Peak lava dome, no historical eruptions were recorded on Montserrat until 1995. Long-term small-to-moderate ash eruptions beginning in that year were later accompanied by lava-dome growth and pyroclastic flows that forced evacuation of the southern half of the island and ultimately destroyed the capital city of Plymouth, causing major social and economic disruption.

ST. HELENS Washington, USA 46.20°N, 122.18°W; summit elev. 2,549 m

Data from deformation-monitoring instruments indicated that during 18-24 July lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds inhibited visual observations.

Geologic Summary. Prior to 1980, Mount St. Helens formed a conical, youthful volcano sometimes known as the Fuji-san of America. During the 1980 eruption the upper 400 m of the summit was removed by slope failure, leaving a 2 x 3.5 km horseshoe-shaped crater now partially filled by a lava dome. Mount St. Helens was formed during nine eruptive periods beginning about 40-50,000 years ago, and has been the most active volcano in the Cascade Range during the Holocene. The modern edifice was constructed during the last 2,200 years, when the volcano produced basaltic as well as andesitic and dacitic products from summit and flank vents. Historical eruptions in the 19th century originated from the Goat Rocks area on the N flank, and were witnessed by early settlers.

UBINAS Perú 16.355°S, 70.903°W; summit elev. 5,672 m

Based on a Significant Meteorological Information (SIGMET) advisory, the Buenos Aires VAAC reported that an ash plume from Ubinas rose to an altitude of 6.1 km (20,000 ft) a.s.l. and drifted SE on 22 July. Ash was not identified on satellite imagery.

Geologic Summary. A small, 1.2-km-wide caldera that cuts the top of Ubinas, Peru's most active volcano, gives it a truncated appearance. Ubinas is the northernmost of three young volcanoes located along a regional structural lineament about 50 km behind the main volcanic front of Peru. The upper slopes of the stratovolcano, composed primarily of Pleistocene andesitic lava flows, steepen to nearly 45 degrees. The steep-walled, 150-m-deep summit caldera contains an ash cone with a 500-m-wide funnel-shaped vent that is 200 m deep. Debris-avalanche deposits from the collapse of the SE flank of Ubinas extend 10 km from the volcano. Widespread Plinian pumice-fall deposits from Ubinas include some of Holocene age. Holocene lava flows are visible on the volcano's flanks, but historical activity, documented since the 16th century, has consisted of intermittent minor explosive eruptions.

OL DOINYO LENGAI Tanzania, eastern Africa 2.751°S, 35.902°E; summit elev. 2,890 m

According to news reports, an eruption began at Ol Doinyo Lengai around 19 July, 2007, forcing villagers living near the volcano to evacuate. An article stated that, "...more than 1,500 people, most of them Maasai families, vacated their homes in Ngaresero, Orbalal and Nayobi villages following the tremors that triggered the volcanic eruption." "Villagers are reported to have heard roaring...before the volcano started discharging ash and lava." There were reports of a damaged school and two injuries, but no reports of deaths.

Geologic Summary. The symmetrical Ol Doinyo Lengai stratovolcano is the only volcano known to have erupted carbonatite tephras and lavas in historical time. The prominent volcano, known as "The Mountain of God," rises abruptly above the broad plain S of Lake Natron. The cone-building stage of the volcano ended about 15,000 years ago and was followed by periodic ejection of natrocarbonatite and nephelinite tephra during the Holocene. Historical eruptions have consisted of smaller tephra eruptions and emission of numerous natrocarbonatitic lava flows on the floor of the summit crater. Petrologists first observed the eruption of carbonatitic lava flows in the 1960s. Subsequent more frequent visits have documented long-term lava effusion in the summit crater that would not have been seen from the foot of the volcano.

KILAUEA Hawaii, USA 19.43°N, 155.29°W; summit elev. 1,222 m

During 18-21 July, the E vent and dominant W vent in Kilauea's Pu'u 'O'o produced lava flows. On 18 July, new vents opened in the Puka Nui pit, in the SSW area of Pu'u 'O'o crater, and produced lava flows that ponded. On 20 July, a vent high on the S crater wall, adjacent to the Puka Nui Gap pit, produced spatter and propelled lava bombs 10 m into the air. Meanwhile, the lava lake in the West Gap pit continued to fill, overturn, and occasionally overflow. The spatter cone that built up around the S wall vent in West Gap pit was submerged beneath the lava lake surface on 20 July. Uplift of the crater interior continued. Earthquakes occurred beneath the upper E rift zone, S flank, and Halema'umau crater.

On 20 July, just before midnight, Pu'u 'O'o's crater floor started to subside; a tiltmeter recorded a nearly 300 microradian tilt change. Just after midnight, on 21 July, the West Gap lava lake and Puka Nui pit drained. A new eruption initiated along a set of fissures that extended 1.7 km E from a point about 150 m E of the E rim of Pu'u 'O'o crater. Preliminary reports described two 600-800 m long, left-stepping fissures between Pu'u 'O'o and Kupaianaha. The easternmost fissure fed two lava flows; the farthest extent of the flow was 1-1.5 miles from the fissure in the SE direction.

On 22 July, HVO reported that the westernmost fissure was inactive by mid-morning on 21 July and the uppermost segment of the active lower fissure was completely sealed by mid-morning on 22 July. The rest of the fissure erupted lava, constructing several small perched ponds. A perched pond at the upper segment of the active fissure breached and produced an a'a' flow that traveled 300-400 m to the E. At Pu'u 'O'o crater, several new cracks were observed around its rim, parts of which had collapsed. During 23-24 July, lava ponds surrounding lower fissure segments grew in thickness and spilled lava over their edges.

Geologic Summary. Kilauea, one of five coalescing volcanoes that comprise the island of Hawaii, is one of the world's most active volcanoes. Eruptions at Kilauea originate primarily from the summit caldera or along one of the lengthy E and SW rift zones that extend from the caldera to the sea. About 90% of the surface of Kilauea is formed by lava flows less than about 1,100 years old; 70% of the volcano's surface is younger than 600 years. The latest Kilauea eruption began in January 1983 along the E rift zone. This long-term ongoing eruption from Pu'u 'O'o-Kupaianaha has produced lava flows that have traveled 11-12 km from the vents to the sea, paving broad areas on the S flank of Kilauea and adding new land beyond the former coastline.

TUNGURAHUA Ecuador 1.47°S, 78.44°W; summit elev. 5,023 m

IG reported that during 18-24 July, intermittently visible ash plumes from Tungurahua rose to altitudes of 5.2-8 km (17,100-26,200 ft) a.s.l. and drifted NW, W, and SW. Ashfall was reported from areas SW and W during 19-21 and 24 July. On 20 July, mudflows were reported from drainages to the NW. On 21 July, a steam-and-gas plume drifted W. On 21, 22, and 24 July, ash plumes were occasionally accompanied by roaring sounds, "cannon shots", or noises that resembled blocks rolling down the flanks.

Geologic Summary. The steep-sided Tungurahua stratovolcano towers more than 3 km above its northern base. It sits ~140 km S of Quito, Ecuador's capital city, and is one of Ecuador's most active volcanoes. Historical eruptions have been restricted to the summit crater. They have been accompanied by strong explosions and sometimes by pyroclastic flows and lava flows that reached populated areas at the volcano's base. The last major eruption took place from 1916 to 1918, although minor activity continued until 1925. The latest eruption began in October 1999 and initially prompted temporary evacuation of the entire town of Baños on the N side of the volcano.

FUEGO Guatemala 14.47°N, 90.88°W; summit elev. 3,763 m

INSIVUMEH reported that during 17-18 July, 2007, gas plumes from Fuego rose to an altitude of 3.9 km (12,800 ft) a.s.l. and drifted SW. On 18 July, a hot lahar, 20 m wide and 1.5 m high, carried blocks 1-1.5 m in diameter to the W down the Santa Teresa ravine. On 20 July, the seismic network recorded 21 explosions. Associated ash plumes rose to altitudes of 4.1-4.7 km (13,500-15,400 ft) a.s.l. and drifted W and SW. Rumbling noises were reported.

Mt Cleveland, Aleutian Islands, USA 52.82°N, 169.95°W; summit elev. 1,730m

AVO raised the Volcanic Alert Level for Cleveland from Advisory to Watch and the Aviation Color Code from Yellow to Orange on 20 July, 2007. The change in Alert Level was based on the presence of an intense thermal anomaly in the crater and associated steam-and-gas plume observed on satellite imagery. The thermal anomaly continued to be detected on satellite imagery during 22-23 July.

KARYMSKY Kamchatka Peninsula, Russia 54.05°N, 159.43°E; summit elev. 1,536 m

Seismic activity at Karymsky was above background levels during 13-20 July, with 500-900 shallow earthquakes occurring daily. Based on seismic interpretation, ash plumes may have risen to altitudes as high as 4.5 km (14,800 ft) a.s.l. Ash plumes drifted SE and SW and a thermal anomaly in the crater were visible on satellite imagery during 14-18 July. Plumes rose to estimated altitudes of 4.5 km (14,800 ft) a.s.l. based on atmospheric profiles. The Level of Concern Color Code remained at Orange.

Based on satellite imagery, the Tokyo VAAC reported that an ash plume rose to an altitude of 5.2 (17,000 ft) a.s.l. on 20 July and drifted SW.

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 about 7,600-7,700 radiocarbon years ago. Construction of the Karymsky stratovolcano began about 2,000 years later. The latest eruptive period began about 500 years ago, following a 2,300-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. Most seismicity preceding Karymsky eruptions has originated beneath Akademia Nauk caldera, which is located immediately S of Karymsky volcano and erupted simultaneously with Karymsky in 1996.