November 23 , 2017 . EN . Great Sitkin , Agung , Nevado del Ruiz , Aira ( Sakurajima) .
November 23 , 2017 .
Great Sitkin , Aléoutiennes :
VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA) .
Issued: November 22 , 2017
Volcano:Great Sitkin (VNUM #311120)
Current Color Code:YELLOW
Source:Alaska Volcano Observatory
Volcano Location:N 52 deg 4 min W 176 deg 6 min
Summit Elevation:5709 ft (1740 m)
Volcanic Activity Summary:
Recent observations of a robust steam plume and a period of gradually increasing seismicity over several months indicate that Great Sitkin Volcano has become restless and is exhibiting behavior that is above background levels. AVO is thus raising the aviation color code and volcano alert level to YELLOW/ADVISORY.
Photographs of the volcano taken by local observers on Sunday, November 19 show a light-colored vapor plume rising about 300 m (1,000 ft) above the vent area and extending about 15-20 km (9 –12 mi) to the south. Nothing unusual was observed in seismic or infrasound data around the time the photographs were taken and nothing noteworthy has been observed in satellite data since the emissions were observed.
An increased number of small earthquakes was evident as early as late July 2016, and since then the level of seismic activity has fluctuated at low levels but has exhibited a gradual overall increase most notable since June 2017. Seismic activity to date has been characterized by earthquakes that are typically less than magnitude 1.0 and range in depth from near the summit of the volcano to 30 km below sea level. Most earthquakes are in one of two clusters, beneath the volcano’s summit or just offshore the northwest coast of the island. The largest earthquake so far was a magnitude 2.8 on September 29, 2017.
Possible explosion signals were observed in seismic data on January 10 and July 21 of this year, but no confirmed emissions were observed locally or detected in infrasound data or satellite imagery. Great Sitkin has experienced at least one other episode of unrest characterized by vigorous steaming. This last occurred in 1953 but no subsequent eruptive activity developed. Minor steaming in the vicinity of the 1974 lava dome was observed in 1986 and in 2012 but no associated eruptive activity occurred.
Great Sitkin Volcano is monitored by a five-station seismic network on Great Sitkin Island and with additional seismic stations on the nearby islands of Igitkin, Adak, Kagalaska, and Kanaga. A six-element infrasound array to detect explosions (atmospheric pressure waves), was installed on Adak Island in June, 2017. AVO also uses satellite imagery to monitor Great Sitkin Volcano.
The current unrest is likely the result of magma intrusion beneath the volcano. Typically, such intrusions release gas, which can increase stress in the crust and lead to an increase in the number of earthquakes. If gases build up near the surface, they may be released suddenly in small explosions or robust emissions.
It is possible, but not certain, that the volcano may eventually erupt. Prior to a significant eruptive event an even greater increase in seismicity should occur as magma rises to shallower levels in the crust. An ash-producing eruption similar to the most recent historical eruption in 1974 could generate airborne ash that may pose hazards to aircraft. Ash fallout on the nearby community of Adak and the surrounding ocean may also occur.
Great Sitkin Volcano is a basaltic andesite volcano that occupies most of the northern half of Great Sitkin Island, a member of the Andreanof Islands group in the central Aleutian Islands. It is located 43 km (26 miles) east of the community of Adak. The volcano is a composite structure consisting of an older dissected volcano and a younger parasitic cone with a 3-km-diameter summit crater. A steep-sided lava dome, emplaced during an eruption in 1974, occupies the center of the crater. Great Sitkin erupted at least three times in the 20th century, most recently in 1974. That eruption produced at least one ash cloud that likely exceeded an altitude of 25,000 ft above sea level. A poorly documented eruption occurred in 1945, also producing a lava dome that was partially destroyed in the 1974 eruption. Within the past 280 years a large explosive eruption produced pyroclastic flows that partially filled the Glacier Creek valley on the southwest flank.
Source : AVO
Photos : Beauparlant, Alain ( November 19 , 2017 ) , Clifford, Roger ( 2012)
Agung , Indonesia :
Based on the analysis of visual and instrumental data and considering potential threats of danger, on October 29, 2017 at 16:00 WITA, the status of G. Agung was lowered from Level IV (Awas) to Level III (Siaga). From yesterday until today visually the volcano is clearly visible until the appearance of the mist. A thick, medium smoke rises from the crater, with a mean pressure, which reaches a height of about 300 to 800 m above the summit. Seismographs recorded tremor vibrations with a constant amplitude of 2 to 5 mm (mainly 3 mm).
On November 22, 2017 the seismograph recorded:
11 shallow volcanic earthquakes (VB) –
9 volcanic earthquakes (VA) –
4 harmonic earthquakes
2 Local Tectonic Earthquakes (TL) –
5 Far Tectonic Earthquakes (TJ)
The communities and mountaineer / visitors / tourists must not ride or carry out any activity in the danger zone, in the area of the G Agung crater and in the whole area of a 6 km radius around the crater of G Agung. Sectoral expansion has been added to the North-North-East, South-South-East and South-West up to 7.5 km. The estimated area hazards are dynamic and continuously assessed and can be modified at any time based on the most recent observational data from G. Agung.
Source : VSI / Magma
Nevado del Ruiz , Colombia :
Subject: Bulletin of activity of the Nevado del Ruiz volcano.
The level of activity continues at the level: Yellow activity level or (III): changes in the behavior of volcanic activity.
With regard to monitoring the activity of the Nevado del Ruiz volcano, the COLOMBIAN GEOLOGICAL SERVICE informs that:
During the last week, the various monitoring parameters show that the Nevado del Ruiz volcano continues to display unstable behavior.
The seismicity caused by the fracturing of the rocks that make up the volcano, has shown an increase in the number of earthquakes and seismic energy released during the last week. The seismic increase recorded on November 19, located northeast of Arenas crater, at depths between 3.5 and 5.0 km is highlighted. During this increase, the earthquake of greatest magnitude occurred at 05:23 (local time) with a magnitude of 1.9 ML (local magnitude) and is also the largest magnitude earthquake recorded in the week. In addition, the seismic activity has been present in the distal sources of the North, South-East, South-West and, to a lesser extent, in the Arenas crater. The depths of the earthquakes varied between 0.5 and 7.0 km.
The seismic activity associated with fluid dynamics within the channels of the volcanic structure showed similar levels, in number of earthquakes and released seismic energy, to those recorded the previous week. This type of activity has been characterized by the occurrence of multiple fluid earthquakes, long period and very long period events, as well as pulses of low energy tremors. The earthquakes were mainly located around the crater Arenas and in the crater itself.
Volcanic deformation measured from electronic inclinometers, Global Navigation Satellite System (GNSS) stations and radar images shows stability behavior without recording significant deformation processes of the volcanic structure. The volcano continues to emit water vapor and gases into the atmosphere, among which the sulfur dioxide (SO2) is distinguished, as evidenced by the values obtained by the SCANDOAS stations installed on the volcano and the analysis satellite images. In tracking the information provided by the MIROVA and NASA FIRMS portals, a thermal anomaly was reported in the vicinity of the Arenas crater on 20 November.
The column of gas and steam reached a maximum height of 2150 m measured at the top of the volcano on November 15. The direction of the dispersion of the column was governed by the direction of the wind in the zone, which during the week prevailed towards the Southeast compared to the crater Arenas.
The Nevado del Ruiz volcano continues at the level of yellow activity.
Source : SGC
Aira ( Sakurajima) , Japan :
Elevation 1117 m
JMA reported that an explosion at Minamidake summit crater (at Aira Caldera’s Sakurajima volcano) detected at 2207 on 13 November, ejected material as far as 1.3 km. The explosion vibrated structures in Kagoshima and Miyazaki prefectures. Poor weather conditions prevented views of a plume. An explosion at Showa Crater at 0955 on 14 November produced a plume that rose 1.3 km above the crater rim.
Another explosion at Minamidake occurred at 2343 on 14 November, generating a plume that rose 1.3 km above the crater rim. Sulfur dioxide flux measured that same day was 1,400 tons per day, up from 400 tons per day on 10 November. Very small events at Minamidake were occasionally detected during 17-20 November. The Alert Level remained at 3 (on a 5-level scale).
Source: Agence météorologique japonaise (JMA), GVP.
Photo : K Arima