Bulletin of the Global Volcanism Network
Volume 34, Number 5, May 2009
Karangetang (Indonesia) Elevated seismicity, lava flows in May 2009;
high alert, evacuations
Ibu (Indonesia) Thermal data suggest dome growth continued into mid 2009
Semeru (Indonesia) Many ash plumes and some pyroclastic flows during
February 2007-March 2009
Slamet (Indonesia) During April-June 2009, minor explosive eruptions
with occasional lava fountains
Krakatau (Indonesia) Variable eruptive activity from late 2007 to
mid-2009; plumes to 3 km altitude
Telica (Nicaragua) Intermittent ash explosions and incandescence
during 2000-2002
Unnamed [E Gakkel Ridge] (N Atlantic) Undated explosive volcanism at
depth on Arctic mid-ocean ridge
Ol Doinyo Lengai (Tanzania) Minor spattering, explosions, ash falls,
and lava flows through April 2009
Editors: Rick Wunderman, Edward Venzke, and Sally Kuhn Sennert
Volunteer Staff: Russell Ross, Paul Berger, Hugh Replogle, Robert
Andrews, Catie Carter, Margo Morell, Jacquelyn Gluck, Stephen Bentley,
William Henoch, Ludmila Eichelberger, and Jeremy Bookbinder
Karangetang [Api Siau]
Sangihe Islands, Indonesia
2.78°N, 125.40°E; summit elev. 1,784 m
All times are local (= UTC + 8 hours)
Lava flows from Karangetang (figure 1) reached several kilometers in
length by the end of May 2009, and some residents evacuated. Witnessed
plumes were minor, many below 100 m above the summit, the tallest 700
m above the summit. Intermittent minor activity, including explosions,
ashfall, and thermal anomalies, has continued in the last few years
(BGVN 32:05, 32:08, 34:01), with no significant changes since 2007
(figure 2 and 3).
Figure 1. Map of the islands in the region around Karangetang,
including Java, Bali, and Sulawesi (Celebes). Karangetang resides at
upper right on Siau island, which is ~ 24-km-long, too small to see at
this scale. (inset) An enlarged satellite image of Karangetang; white
areas are clouds over volcanic peaks on the island. Maps have N
directly upwards; scale bars are at lower left. Both maps courtesy of
Google Earth.
Figure 2. A 2007 photo of Karangetang taken from the sea (direction
unspecified) showing multiple peaks and abundant unvegetated lava
flows of young ages. The more distant cone may have been steaming.
Photo by Mark Tolosa.
Figure 3. A photo of the summit area at Karangetang taken from the
observatory station at Salili, S of the volcano, on 13 August 2007.
Lava flows and rock avalanches during 2007 were not directly visible
from this point. Note the rugged topography of the active lava dome at
the summit. Courtesy of Arnold Binas.
Based on a pilot observation, the Darwin VAAC reported that on 24 May
an ash plume from Karangetang rose to an altitude of 3.7 km and
drifted 75 km S. This was the tallest plume of the reporting interval.
On 31 May, based on seismicity, an increase in both volcanic tremor,
and continuous air blasts (accompanied by rumbling sounds), the Center
of Volcanology and Geological Hazard Mitigation (CVGHM) upgraded
Karangetang's hazard status from Alert Level 3 (Siaga) to 4 (Awas) the
highest level (figure 4). According to the website "Natural Disasters
in Indonesia," hundreds of people were evacuated from near the volcano
and the total number of vulnerable residents was 3,000. The Alert
Level fell back to 3 on 9 June.
Figure 4. Alert levels applicable to Karangetang (and commonly used in
Indonesia) with brief explanation of their significance. From the
Natural Disasters in Indonesia website.
Tremor was reported on 30 May and became continuous at times during
the morning of on 31 May (0600-1200). That same time interval saw the
largest number of earthquakes. Craters I and II initially produced
white plumes to heights of ~ 10-25 m and visible incandescence.
Beginning at 0630 a dense white to brownish plume from the principal
crater reached a height of ~ 100 m above the peak. At 0824 there was a
continuous expulsion of lava which flowed S, traveling ~ 2.3 km down
the Kali Batuawang river. Lava also flowed ~ 1.5 km into the Kali
Kahetang and Kali Keting rivers. Lava flows periodically traveled ~ 1
km down the Kali Nanitu and Batang rivers. At 0828 a thick grayish to
plume was continuously ejected to a height of ~ 25-700 m accompanied
by a rumbling sound of low to medium intensity.
In connection with the upgrading of the hazard status to Alert Level
4, CVGHM stepped up its monitoring and sent a team to the field. The
regional government was alerted to the possible fallout of hot ash and
the expulsion of lava flows. Numerous threatened towns and
sub-districts were mentioned. These included Siau Timur, Kampung
Kola-Kola (Bebali village); Kampung Bolo and Kampung Kopi, (Tarorane
village); Kampung Hekang, Tatahadeng village, the village of Dame 1,
the village of Karalung along the Kali Beha Timur river and, Kampung
Dompase, along the banks of the Kali Nanitu and Kali Kinali rivers.
There was the constant threat of lahar (mud flows) along the length of
the rivers that originate from the active crater, including the Batu
Awang, Kahetang, Keting, Batang, Beha Timur, and Nanitu rivers.
People were cautioned not to approach Karangetang closer than 3 km
from the summit, particularly under conditions of heavy rain.
Residents of the village of Dame and part of the population of the
township of Tatahadeng were advised to maintain a high level of
alertness to the dangers of pyroclastic flows and lava flows. In the
case of sudden tephra falls, authorities recommended the public don
face masks. As previously mentioned, on 9 June 2009 the alert level
was reduce from 4 to 3.
MODVOLC. There were numerous MODVOLC thermal alerts during 2 December
2008-25 February 2009 (BGVN 34:01). As of late June 2009, dates of
subsequent MODVOLC alerts for Karangetang were 18 and 29 March; 25,
26, 28, and 30 April; and 7, 14, and 31 May; and 3 June. In effect,
the alerts were broadly spread for more than a year and showed little
if any response to the elevated activity seen during the crisis.
Geologic Summary. Karangetang (Api Siau) volcano lies at the N end of
the island of Siau, N of Sulawesi. The 1,784-m-high stratovolcano
contains five summit craters along a N-S line. Karangetang is one of
Indonesia's most active volcanoes, with more than 40 eruptions
recorded since 1675 and many additional small eruptions that were not
documented in the historical record (Catalog of Active Volcanoes of
the World: Neumann van Padang, 1951). Twentieth-century eruptions have
included frequent explosive activity sometimes accompanied by
pyroclastic flows and lahars. Lava dome growth has occurred in the
summit craters; collapse of lava flow fronts has also produced
pyroclastic flows.
Information Contacts: Center of Volcanology and Geological Hazard
Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia
(URL: http://portal.vsi.esdm.go.id/joomla/); Hawai'i Institute of
Geophysics and Planetology (HIGP) Thermal Alerts System, School of
Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525
Correa Road, Honolulu, HI 96822, USA (URL:
http://hotspot.higp.hawaii.edu/); Darwin Volcanic Ash Advisory Centre
(VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO
Box 40050, Casuarina, NT 0811, Australia (URL:
http://www.bom.gov.au/info/vaac/); Agence France-Presse (URL:
http://www.afp.com/); Arnold Binas, Toronto, Canada (Email:
abinas@xxxxxxxxx; URL:
http://www.summitpost.org/user_page.php?user_id=42443,
http://www.flickr.com/photos/hshdude/collections/72157600584144439/).
Ibu
Halmahera, Indonesia
1.488°N, 127.63°E; summit elev. 1,325 m
All times are local (= UTC + 9 hours)
Our last report on Ibu summarized MODVOLC thermal alerts (satellite
thermal anomalies) from mid-May through late October 2008 (BGVN
33:09); those anomalies continued to be recorded almost monthly
through June 2009. The anomalies suggest continued growth of a lava
dome in the crater, an event previously documented by a photograph
taken May 2000 and mentioned in BGVN 28:03. Authorities raised the
hazard alert to Level 3 during June 2008. Several photos of Ibu in
2007 were taken by Arnold Binas (figure 5).
Figure 5. Photos of Ibu taken on 27 July 2007 from a point on the NW
crater rim, looking approximately SE. The top photo shows the location
of the dome in the steep-walled crater. The bottom photo shows a
close-up view of the dome. Courtesy of Arnold Binas.
Geologic Summary. The truncated summit of Gunung Ibu stratovolcano
along the NW coast of Halmahera Island has large nested summit
craters. The inner crater, 1 km wide and 400 m deep, contained several
small crater lakes through much of historical time. The outer crater,
1.2 km wide, is breached on the N side, creating a steep-walled
valley. A large parasitic cone is located ENE of the summit. A smaller
one to the WSW has fed a lava flow down the western flank. A group of
maars is located below the northern and western flanks of the volcano.
Only a few eruptions have been recorded from Ibu in historical time,
the first a small explosive eruption from the summit crater in 1911.
An eruption producing a lava dome that eventually covered much of the
floor of the inner summit crater began in December 1998.
Information Contacts: Center of Volcanology and Geological Hazard
Mitigation (CVGHM), Saut Simatupang, 57, Bandung 40122, Indonesia
(URL: http://portal.vsi.esdm.go.id/joomla/); Hawai'i Institute of
Geophysics and Planetology (HIGP) Thermal Alerts System, School of
Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525
Correa Road, Honolulu, HI 96822, USA (URL:
http://hotspot.higp.hawaii.edu/); Arnold Binas, Toronto, Canada
(Email: abinas@xxxxxxxxx; URL:
http://www.summitpost.org/user_page.php?user_id=42443,
http://www.flickr.com/photos/hshdude/collections/72157600584144439/).
Semeru
Java, Indonesia
8.108°S, 112.92°E; summit elev. 3,676 m
All times are local (= UTC + 7 hours)
Our last report (BGVN 32:03) covered through October 2006 in terms of
CVGHM reporting and through February 2007 in terms of Darwin VAAC
reporting. As has been the case for decades, Semeru's eruptions
continued and were ongoing through this reporting interval, February
2007-March 2009. During the reporting interval, ash plumes were
periodically observed over the summit at low altitudes of 3.7-4.6 km.
Taller plumes, when they occurred, are noted below. There were several
cases of plumes over 6 km altitude and as tall as ~ 7.6 km altitude.
Pyroclastic flows ran out to distances as great as 3 km (table 1).
Table 1. Compilation of data on Semeru during February 2007-March
2009. Courtesy of CVGHM.
Date Plume height and Seismicity and
drift direction Observations
10-11 Feb 2007 E --
03-05 May 2007 4.6 km; SW --
25 May 2007 4.6 km; W --
18-25 Jun 2007 4.2 km --
06 Aug 2007 6.1 km --
22 Sep 2007 7.3 km --
31 Oct 2007 -- Eruption heard 17 km away
21 Apr 2008 6.1 km --
15, 17-19, -- Increased seismicity.
Pyroclastic flows up to 500-3000
21 May 2008 m from the crater. On 21
May, incandescent ejections.
22 May 2008 -- Fewer pyroclastic flows and
rockfalls; four up to
2.5 km from crater.
05 Jun 2008 -- Decline in seismicity.
07-09 Jul 2008 4.9-7.6 km; SSW --
27 Jul 2008 4.3 km --
05 Aug 2008 4.0-4.3 km Plumes sometimes with
incandescent tephra.
07 Aug 2008 4.3 km Incandescent material ejected
from the crater
21-22 Aug 2008 3.7 km; W --
28 Aug 2008 Low-level --
31 Aug 2008 4.6 km; SW --
09 Sep 2008 4.3 km; SSW --
10 Sep 2008 4.3 km --
22 Oct 2008 4.3 km --
Jan 2009 -- Average over 100 daily
eruptive earthquakes. Four deep
volcanic earthquakes on the 24th.
Feb 2009 -- Average of less than 50
eruptive earthquakes/day.
01 Feb 2009 4.0 km --
21 Feb 2009 -- 18 deep volcanic earthquakes.
03 Mar 2009 -- 5 eruptive earthquakes.
06 Mar 2009 3.7 km 0010 local time (see text)
06, 12 Mar 2009 -- Volcanic seismicity had a
maximum amplitude reached
+- 34 mm.
12 Mar 2009 4.5 km Ash/cinder eruption
accompanied by rumbling sounds
lasting ~ 6 minutes
15 Mar 2009 4.3 km Eruptive earthquake amplitude
+-18 mm. Dense
low-pressure ash-cinder
eruption; changing to white
air-blasts, then gradually
diminishing.
16-22 Mar 2009 -- Averaged eruptive earthquakes
around 1-30 daily; max.
amplitudes less than 10 mm.
October 2007. Based on reports from CVGHM, the Darwin VAAC reported
that an unconfirmed eruption was heard 17 km away on 31 October 2007
(table 1). No plume was seen in MTSAT-IR satellite imagery. A news
report from ANTARA News on 5 November 2007 ("Ash blankets town near
Indonesian volcano") noted that scientists monitoring the volcanoes
confirmed Semeru as the source. The news report stated that initially
residents thought the thin layer of ash had come from Kelut, a volcano
that went to Alert Level 4 (the highest status) on 16 October. The
eruption of Kelut, while emitting a large dome into a crater lake,
triggered few if any sustained explosions (BGVN 33:03). Ash fell in
Blitar, outside a 10 km danger zone around Kelut; Semeru is ~ 90 km
away.
On 15, 17-19, and 21 May 2008 ash plumes, rockfall avalanches, and
multiple pyroclastic flows were observed, as well as increased seismic
activity. At that time, the alert level was raised from 2 to 3. By 22
May pyroclastic flows and rockfall avalanches had declined in
frequency, and consequently on 5 June the hazard was lowered to Level
2. During 7-9 July 2008, ash plumes rose to altitudes of 4.9-7.6 km,
the tallest of the reporting interval.
From January to mid-February 2009, explosion earthquakes occurred on
average 100-150 times a day (table 1). Ash and cinder eruptions from
Jonggring Saloko crater took place daily every 15-20 minutes, with
plumes reaching altitudes of 3.7-4.3 km. During a ~ 5 minute interval
on 6 March 2009 at 0010, a loud boom was followed by a bluish flash of
lightning 5-7 seconds in duration.
Geologic Summary. Semeru, the highest volcano on Java, and one of its
most active, lies at the southern end of a volcanic massif extending N
to the Tengger caldera. The steep-sided volcano, also referred to as
Mahameru (Great Mountain), rises abruptly to 3,676 m above coastal
plains to the south. Gunung Semeru was constructed S 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. Semeru has
been in almost continuous eruption since 1967.
Information Contacts: Center of Volcanology and Geological Hazard
Mitigation (CVGHM), Saut Simatupang, 57, Bandung 40122, Indonesia
(URL: http://portal.vsi.esdm.go.id/joomla/); ANTARA News (URL:
http://www.antara.co.id/en/).
Slamet
Java, Indonesia
7.242°S, 109.208°E; summit elev. 3,428 m
All times are local (= UTC + 7 hours)
Minor eruptions were reported at the active crater during April-June
2009. Small amounts of ash fell several times during May. Witnesses
saw lava fountains on 12 and 21-23 May. Previously, steam plumes were
associated with heavy rains during 28 March-3 April 2007 (BGVN 33:04).
During 19-23 April 2009 Slamet's seismicity increased. On 20 April,
diffuse white plumes rose ~ 50 m above the crater. During 21-23 April,
the number of eruption tremors increased steadily, and dense,
white-to-brownish plumes rose 50-800 m above the crater rim. The Alert
Level was raised to 2 (on a scale of 1-4).
On 23 April, the Alert Level was raised to 3; people were advised not
to climb the summit. According to a news article in the Jakarta Globe,
a volcanologist from the Center of Volcanology and Geological Hazard
Mitigation (CVGHM) stated that lava was ejected 600 m high and ash
bursts occurred up to 112 times within a 6-hour period.
According to CVGHM, seismicity continued to increase or remain
elevated during 23 April-17 May, peaking on 17 May. During this
period, continuous eruptive quakes/tremors were recorded, together
with an increase in amplitude (3-46 mm on 12-13 May, rising to about
20-32 mm between 17-24 May). Eruptions from the western part of the
crater continued, and inflation was noted. During times of clear
weather, observers reported that incandescent lava was ejected 25-100
m above the crater, and then fell back into and around the active
crater. Gray and white "smoke" rose 100-800 m from the crater.
Occasionally a thunderous noise accompanying eruptions of ash
occurred, and ashfall was detected in areas 5-9 km away. The
temperature of water in several locations on the flanks increased.
During 12 May and 21-23 May, lava fountains rose 100-400 m above the
crater rim. During several eruptions, ejected incandescent material
traveled down the W flank. White-to-gray "smoke" rose 150 m above the
crater. On 22 May, ashfall was reported in Sawangan village, 5 km W.
On 23 May, an ash plume rose 1 km above the crater and ash fell on the
N flank. Ash accumulated to 1 mm depth near the observation post. The
next day an ash plume rose 700 m above the crater.
Based on ground information from CVGHM, the Darwin Volcanic Ash
Advisory Centre (VAAC) reported that on 27 May an ash plume from
Slamet rose to an altitude of 4.3 km. Analysis of satellite imagery
also indicated that a possible plume rose to an altitude of 6.1 km,
but ash was not conclusively detected.
CVGHM reported that during 26 May-4 June activity from Slamet
fluctuated, but decreased overall. They found decreases in both the
number of earthquakes and the temperature of water in areas around the
volcano. Inflation and deflation fluctuated within a range of 2 cm.
White plumes rose 100-750. During 5-7 June, activity was characterized
by inflation and an increased number of earthquakes. During that time,
white plumes were accompanied by ash emissions that rose 200-800 m
from the crater, incandescent material was ejected 50-200 m above the
crater, and booming noises were reported.
As of 4 June 2009, the Alert Level remained at 3, based on visual
data, deformation, earthquakes, and tremor. CVGHM urged the public to
don face masks during heavy ashfalls, and to cover water sources to
prevent contamination by volcanic ash.
Geologic Summary. Slamet, Java's second highest volcano at 3,428 m and
one of its most active, has a cluster of about three dozen cinder
cones on its lower SE-NE flanks and a single cinder cone on the
western flank. Slamet is composed of two overlapping edifices, an
older basaltic-andesite to andesitic volcano on the west and a younger
basaltic to basaltic-andesite one on the east. Gunung Malang II cinder
cone on the upper eastern flank on the younger edifice fed a lava flow
that extends 6 km to the east. Four craters occur at the summit of
Gunung Slamet, with activity migrating to the SW over time. Historical
eruptions, recorded since the 18th century, have originated from a
150-m-deep, 450-m-wide, steep-walled crater at the western part of the
summit and have consisted of explosive eruptions generally lasting a
few days to a few weeks.
Information Contacts: Center of Volcanology and Geological Hazard
Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia
(URL: http://portal.vsi.esdm.go.id/joomla/); Darwin Volcanic Ash
Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory
Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL:
http://www.bom.gov.au/info/vaac/); Jakarta Globe (URL:
http://www.thejakartaglobe.com).
Krakatau
Indonesia
6.102°S, 105.423°E; summit elev. 813 m
All times are local (= UTC + 7 hours)
Renewed eruptive activity from Anak Krakatau began in October 2007
(BGVN 32:09), with minor eruptions through that November (BGVN 33:01).
This small but growing post-caldera cone first gained attention with a
1927 eruption (Simkin and Fiske, 1983). During October-November 2007
several eruptions were Vulcanian in nature (BGVN 33:01). The detailed
chronology of behavior during October 2007 to 3 July 2009 is sometimes
sketchy, but activity was apparently quite variable. Although one or
more lulls may have occurred, eruptions clearly continued into 2009.
Many of these eruptions were minor, but some were large enough to
cause the Center of Volcanology and Geological Hazard Mitigation
(CVGHM) to raise the Alert Level to 3 (on a scale with 4 as the
highest). The Alert Level was lowered and raised again throughout 2008
and into 2009 as activity warranted. People were advised not to go
within 1.5 km of the summit.
During April 2009 some residents in neighboring Sumatra allegedly
evacuated when they saw more intense activity (including plumes up to
~ 1 km above the crater). Some of the taller plumes during the
reporting interval rose to ~ 3 km.
Activity through August 2008. According to a news article, by 22
November 2007, seismicity had declined in frequency. Based on an
Antara News article, this decline in seismic activity was interrupted
by incandescent rock ejections on 20 January 2008 accompanied by
plumes that rose to altitudes of 2.8-3.3 km. Eruptions reportedly had
a "deafening sound" and could be seen from Sertung and Rakata islands.
Seismicity again declined in early February 2008, and eruption plumes
and ejected incandescent material were not seen during 4 February to
mid-April 2008.
Seismicity increased during 14-21 April 2008, with the number of
events per day peaking on 20 April. Ash plumes accompanied by ejected
incandescent rocks were noted during CVGHM field observations on 16,
17, and 18 April. The eruption affected the summit and the E and S
flanks. Booming noises were reported and occasionally heard at an
observation post 42 km away.
Based on observations of satellite imagery and pilot reports, the
Darwin Volcanic Ash Advisory Center (VAAC) reported that a low-level
ash plume on 20 June 2008 rose to an altitude of 3 km and drifted NW.
During 22 June-1 July 2008, the number of seismic events decreased
significantly and booming noises were less frequently heard. On 1-3
July ash emissions declined, although on 1 and 2 July low level ash
plumes rose to an altitude less than 3 km and drifted NW.
Based on observations of satellite imagery, the Darwin VAAC reported
that ash plumes from Anak Krakatau rose to an altitude of 3 km on 27
July 2008 and drifted NW.
According to an article in Antara News, eruptions increased in
frequency during 10-11 August 2008. On 12 August, monitoring personnel
reported that active lava flows and dense emissions of "smoke"
continued, but that the frequency of earthquakes and eruptions had
declined. Another news article indicated that explosions and
earthquakes averaged ~ 120 per day during 11-17 August 2008.
Monitoring personnel during that period observed plumes, active lava
flows, and rock ejections.
Activity during March-May 2009. No additional reports by CVGHM were
available during September 2008 through February 2009. Alerts based on
thermal anomalies (see MODVOLC section, below) were not present during
31 August 2008 to 30 March 2009.
Seismicity increased significantly during 19-25 March 2009 and
remained high through 5 May. During periods of clear weather on 25
March, white-to-gray plumes rose 400 m above the volcano. During 27-30
March and 1 April 2009 clear weather revealed ash plumes rising
200-800 m. On 2 April an ash eruption was seen on satellite imagery
and reported by a pilot. A resultant ash plume drifted more than 60 km
S.
During March through 25 April 2009, an episode of heightened
seismicity produced thousands of eruptive signals (table 2); however,
the seismic station shut down overnight during 1-26 April, and
completely shut down during 27-29 April. CVGHM believed that this
shutdown was the result of either blockage of sunlight from reaching
the solar panels by tephra collecting there or because of
impact-induced damage to the panels. On 29 April CVGHM installed a
seismometer on Anak Krakatau at a location thought to be reasonably
safe.
Table 2. Type and number of earthquakes and tremor recorded at
Krakatau during 27 March-6 May 2009. Values shown are daily averages
unless otherwise indicated by footnotes below. (1)Average during 12
hour period (daylight). (2) Starting at 0830 local time from a new,
safer location. (3) During 0000 to 1200 local time. Courtesy of CVGHM.
Date (2009) Eruptive Air-blast Deep Shallow
Tremor Harmonic
volcanic volcanic
tremor
27-30 Mar 175 102 3 68
-- --
31 Mar 152 72 5 32
-- --
01-24 Apr(1) 168 109 12 62
-- --
25-26 Apr(1) 116 -- 2 51
-- --
27-29 Apr No data No data No data No data No
data No data
30 Apr(2) 229 142 -- 12
44 1
01 May 324 248 -- 98
80 4
02 May 318 270 -- 131
126 24
03 May 250 273 -- 71
114 23
04 May 403 230 -- 36
183 38
05 May 371 339 -- 58
127 41
06 May(3) 132 127 -- 44
82 23
During April 2009 observers reported grayish-white to black plumes
that rose to 50-1,000 m above the crater. They heard many loud booms.
CVGHM observations carried out on 24-25 and 29 April found the
eruption venting from a crater near the volcano's peak on its SW
slope. Eruptions generally sent incandescent blocks and ash ~ 500 m
from the center in all directions. Some of the lofted ash blew E to SE
and caused fallout up to 5 km away.
According to a news article on 29 April 2009, some residents in
southern Sumatra near Krakatau evacuated because they had observed
increased volcanism during the previous week. For example, observers
reported loud blasts, lava flows, and ash plumes. In clear weather on
5 May "smoke" rose 500 m above the crater.
An Antara News article published on 18 June 2009 indicated that in the
previous several days the number of small eruptions increased
tremendously. It said that, according to Anto Prambudi, head of the
monitoring post in Pasauran village, at least 828 small eruptions were
recorded during 11-17 June 2009.
MODVOLC. MODVOLC thermal alerts were triggered through 9 December 2007
(BGVN 33:01). In later 2007, comparatively few alerts occurred, but
became more prevalent again during mid-January 2008. After that, they
were few or absent until mid-April; alerts were common and strong
during the week ending 4 May. Consistent alerts were the pattern until
the week ending 7 June, which had no alerts, but some continued in the
next few weeks.
A seven-month gap in MODVOLC thermal alerts occurred during the
interval 31 August 2008 to 30 March 2009. After that, alerts again
became common again, particularly abundant during April 2009 (an
episode of eruptions and heightened seismicity) and continued
regularly through at least 3 July 2008.
The gap in alerts may have been influenced by downward biasing from
poor weather conditions. On the other hand, for the cases with high
numbers of alerts, false positives (due to fires for example) were
unlikely on the desolate landscape of Anak Krakatau.
Reference: Simkin, T., and Fiske, R.S., 1983, Krakatau 1883-the
volcanic eruption and its effects: Smithsonian Institution Press,
Washington, DC, 464 p. [ISBN 0-87474-841-0]
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 AD, 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.
Information Contacts: Center of Volcanology and Geological Hazard
Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia
(URL: http://portal.vsi.esdm.go.id/joomla/); Darwin Volcanic Ash
Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory
Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL:
http://www.bom.gov.au/info/vaac/); Antara News (URL:
http://www.antara.co.id/en/); Jakarta Post (URL:
http://www.thejakartapost.com/).
Telica
Nicaragua
12.602°N, 86.845°W; summit elev. 1,061 m
All times are local (= UTC - 6 hours)
Explosions occurred at Telica during January and through February
2000, after which the activity began to gradually decline (BGVN 25:03
and 25:09). Intermittent ash explosions and crater incandescence were
seen through 2002, along with high levels of seismicity related to
degassing and constant low tremor. The Geophysics Department of the
Nicaraguan Territorial Studies Institute (INETER) monitors activity;
visits to the crater described below are by INETER staff unless
otherwise noted. Many observations were also made by a local resident
who maintains the local seismic station.
Activity during 2000. Tremor remained constant during April-June 2000,
with no ash emissions. Visiting geologists reported incandescence in
the crater on 5 July 2000. INETER workers who reached the crater on 14
July heard a noise like an airplane turbine coming from the crater and
saw glow. They also noted that there had been a widening of the crater
due to wall collapses, and an increase in its depth, although the
crater floor could not bee seen. On 8 August a crater visit revealed
strong fumarolic activity, and sounds resembling gun detonations from
the bottom of a new opening.
Residents living near the crater reported on 6 September that ash
explosions occurred during the evening and plumes drifted NE.
Unfortunately INETER technicians found no traces of ash on 12
September, following rainfall. Small landslides inside the crater were
observed. A characteristic strong smell of sulfur was detected in the
crater area. Due to the change in wind direction that occurs during
September and October, gases and acid rain affected areas to the N,
NE, and E. Intense rainfall caused a mudflow down a W-flank drainage.
In the visit on 27 October there was no exhalation of gases, but
landslides along the south wall sent material onto the crater floor.
Crater visits on 5 and 22 November showed abundant gas output.
Jet-like sounds came from fumaroles on the NE wall. Gas emissions
were low during December. There were minor landslides in the crater,
heard in the last days of November and beginning of December.
Activity during 2001. On the afternoon of 17 January 2001 there were
rumbles and a plume of ash and gases 200 m high. On 19 January a visit
to the crater found ashfall, to a depth of 1 mm, deposited within a
radius of 500 m. The vicinity of the seismic station and SW from the
crater had been affected by acid rain. On 22 January visiting
scientists observed another small explosion. Activity was low during
field visits on 20 and 26 February.
A visit on 3 and 16 March found variable levels of gas emissions.
Incandescence was observed within the new crater early on 21 March
along with increased output gases. Shortly thereafter a loud explosion
was heard, followed by a dark plume about 30 m high and increased
glow, but no ashfall. Activity remained low in April.
INETER staff visited the volcano on 6 June and heard a strong jet-like
sound, but fumarolic emissions were not abundant. Another visit on the
night of 26 June revealed incandescence and landslides inside the
crater. Visits to the volcano were made on 13, 16, and 25 July, but no
volcanic activity was noted. On 15 July the Civil Defense in Leon
informed INETER of sporadic gray ash columns that began the previous
day. A local resident reported hearing an explosion at 0315 on 14
July, and saw five emissions of gas-and-ash later that day. This
activity lasted until 15 July.
A visit on 15 September revealed little gas emission from the crater,
but explosion noises were heard. On 25 October Civil Defense Leon was
informed by several farmers that between approximately 0600 and 1000
local time they had observed a column of ash that drifted NW. INETER
staff working in the area that day observed strong ash accompanied by
expulsion of gas. Rumbling noises and explosions continued until 1430.
On 22 November a visitor observed no change in the volcano. Minor
ashfall was reported on the morning of 18 December, and the next day
explosions were heard coming from the crater.
Activity during 2002. On 17 January 2002 visitors observed strong gas
fumes. Observations on 7 March indicated that the crater was wider and
deeper than in February. On a 10 July visit there were abundant gas
emissions from the crater, a strong smell of sulfur, jet sounds, and
noises of breaking rocks. Gas emissions were abundant on 23 August,
with columns up to 300 m high, but no landslides, noises, sulfur odor,
or incandescence was noted. Rockslides on the N wall of the crater and
sulfur odors, along with typical fumarolic activity, were seen during
September.
Visitors on 17 October reported abundant gas emissions and strong
sulfur odors; noises similar to the movement of waves came from the
crater bottom, and some incandescent points were seen. From 7 to 11
October large quantities of gases blew SE, damaging vegetation.
Landslides were observed SW of the old crater. Fumarole temperatures
were the highest recorded since 1999. Incandescence inside the crater
was also observed over several days. Webcam observations in November
and December showed intermittent small gas emissions.
Geologic Summary. Telica, one of Nicaragua's most active volcanoes,
has erupted frequently since the beginning of the Spanish era. The
Telica volcano group consists of several interlocking cones and vents
with a general NW alignment. Sixteenth-century eruptions were reported
at symmetrical Santa Clara volcano at the SW end of the Telica group.
However, its eroded and breached crater has been covered by forests
throughout historical time, and these eruptions may have originated
from Telica, whose upper slopes in contrast are unvegetated. The
steep-sided cone of 1,061-m-high Telica is truncated by a 700-m-wide
double crater; the southern crater, the source of recent eruptions, is
120 m deep. El Liston, immediately SE of Telica, has several nested
craters. The fumaroles and boiling mudpots of Hervideros de San
Jacinto, SE of Telica, form a prominent geothermal area frequented by
tourists, and geothermal exploration has occurred nearby.
Information Contacts: Direccion General de Geofisica, Instituto
Nicaraguense de Estudios Territoriales (INETER), Apartado Postal 2110,
Managua, Nicaragua (URL:
http://www.ineter.gob.ni/geofisica/geofisica.html).
Unnamed
East Gakkel Ridge, Arctic Ocean
85.58°N, 85.00°E; summit elev. -3,800 m
All times are local (= UTC + 6 hours)
A sonar survey in 2001 along the ultraslow-spreading Gakkel Ridge
(formerly known as the Nansen Cordillera and Arctic Mid-Ocean Ridge)
by the USS Hawkbill submarine and the U.S. Coast Guard icebreaker
Healy revealed two previously undiscovered volcanoes beneath the pack
ice of the Arctic Ocean (BGVN 26:03). In July 2007, a research team
led by Woods Hole Oceanographic Institution (WHOI) uncovered evidence
of explosive volcanic eruptions in the same area of the seafloor.
At a depth of ~ 4 km, researchers found fresh, unweathered, jagged,
glassy fragments of rock (pyroclastic deposits) spread out over an
area of ~ 10 km^2 around a series of small volcanic craters on the
Gakkel Ridge (figure 6). According to WHOI geophysicist Rob
Reves-Sohn, chief scientist of the expedition, as quoted in the 14
August 2008 issue of Oceanus, "These are the first pyroclastic
deposits we've ever found in such deep water, at oppressive pressures
that inhibit the formation of steam, and many people thought this was
not possible. This means that a tremendous blast of carbon dioxide was
released into the water column during the explosive eruption."
Although no speculation was made by the scientists as to the age of
the eruption(s) that caused these pyroclastics, the fresh nature of
these surficial materials argue to their recency.
Figure 6. Detailed bathymetry (30-m grid spacing) of the Gakkel Ridge
at 85ºE in the Arctic Ocean based on July 2007 WHOI research cruise.
The inset map shows the location of the 85°E segment (yellow star)
along the Gakkel ridge (red line) in the Arctic basin. The main panel
shows illuminated, color bathymetry of the 85º E segment acquired
during the Arctic Gakkel Vents (AGAVE) expedition. The axial valley
contains large numbers of distinctive, cratered volcanoes, including a
cone on a fault terrace of the northern valley wall. Photographic
bottom surveys were conducted along profiles shown as thin black lines
on the map. Pyroclastic deposit samples were collected at sites shown
by white circles, and the photographs shown in figure 7 were taken at
the sites shown by the lettered (red) stars. Named features include
two volcanic ridges in the center of the axial valley (Jessica's hill
and Duque's hill), and three cratered volcanoes along a ridge-parallel
fissure to the S (Oden, Thor, and Loke). Courtesy of Sohn and others
(2008).
According to Cochran (2008), the Gakkel Ridge is the slowest spreading
portion of the global system of mid-ocean ridges. Total spreading
rates vary from 12.8 mm/yr near Greenland to 6.5 mm/yr at the Siberian
margin.
A recent article by Sohn and others (2008) concerning the July 2007
expedition noted that roughly 60% of the Earth's outer surface is
composed of oceanic crust formed by volcanic processes at mid-ocean
ridges. Although only a small fraction of this vast volcanic terrain
has been visually surveyed or sampled, the available evidence suggests
that explosive eruptions are rare on mid-ocean ridges, particularly at
depths below the critical point for seawater (a depth of ~ 3,000 m). A
pyroclastic deposit has never been observed on the sea floor below
3,000 m, presumably because the volatile content of mid-ocean-ridge
basalts is generally too low to produce the gas fractions required for
fragmenting a magma at such high hydrostatic pressure. Liu and others
(2008) reported on recent analyses of many major and trace element
collected from Gakkel Ridge.
The July 2007 expedition acquired photographs and video images of
'zero-age' volcanic terrain along the ridge and beneath the ice-cover
ocean's surface. The axial valley at 4,000 m water depth was blanketed
with unconsolidated pyroclastic deposits. Those included bubble-wall
fragments (limu o Pele, also know as Pele's seaweed-fragments of large
glass bubbles that shatter into pieces of curved, paper-thin, bubble
walls), covering a large (greater than 10 km^2) area (figure 7). At
least 13.5 weight percent CO2 is necessary to fragment magma at these
depths, which is about tenfold above the highest values previously
measured in a mid-ocean-ridge basalt.
Figure 7. Photographs of pyroclastic deposits taken during July 2007
WHOI research cruise. (a) One frame from a high-definition video
camera taken on the S side of Duque's hill (see figure 6 for
location). About 10 cm (visually estimated and confirmed during
sampling) of pyroclastic material is piled atop a high-standing,
weathered, pillow feature. The exoskeleton of an as yet unidentified
species of hexactinellid sponge (glass sponge, or a sponge with a
skeleton made of 4- and/or 6-pointed siliceous spicules) is visible in
the foreground. (b) High-definition video frame grab of talus blocks
possibly representing ejecta from a vulcanian explosion on Oden
volcano (see figure 6 for location). (c) Glassy, granular, pyroclastic
material. (d) Bubble wall fragment from pyroclastic deposit. Courtesy
of Sohn and others (2008).
Sohn and others (2008) note that these observations raise important
questions about the accumulation and discharge of magmatic volatiles
at ultraslow spreading rates on the Gakkel ridge. They also
demonstrate that large-scale pyroclastic activity is possible along
even the deepest portions of the global mid-ocean ridge volcanic
system.
References: Sohn, R.A., Willis, C., Humphris, S., Shank, T.M., Singh,
H., Edmonds, H.N., Kunz, C., Hedman, U., Helmke, E., Jakuba, M.,
Liljebladh, B., Linder, J., Murphy, C., Nakamura, K., Sato, T.,
Schlindwein, V., Stranne, C., Tausenfreund, M., Upchurch, L., Winsor,
P., Jakobsson., M., and Soule, A., 2008, Explosive volcanism on the
ultraslow-spreading Gakkel ridge, Arctic Ocean: Nature, v. 453, p.
1236-1238 (doi:10.1038/nature07075).
Cochran, J.R., 2008, Seamount volcanism along the Gakkel Ridge, Arctic
Ocean, Geophysical Journal International, v. 174, no. 3, p. 1153-1173.
Liu,C-Z, Snow, J.E., Hellebrand, E., Brugmann, G., von der Handt, A.,
Buchl, A., and Hofmann, A.W., 2008, Ancient, highly heterogeneous
mantle beneath Gakkel ridge, Arctic Ocean: Nature, v. 452, p. 311-316
(doi:10.1038/nature06688).
Carlowicz, M., 2008, Deeply submerged volcanoes blow their tops:
Telltale rocks reveal evidence of a phenomenon scientists thought was
impossible: Oceanus, 14 August 2008.
Geologic Summary. Two young volcanoes were discovered along the
eastern part of the slow-spreading Gakkel Ridge during a bathymetric
survey from a submarine in 1999. The westernmost volcano showed
evidence of highly reflective, sediment-free surfaces and young faults
overprinted by lava flows. During January-September 1999 global
seismic networks detected an earthquake swarm corresponding to the
approximate location of this volcano. The correlation between the
locations of the earthquake epicenter locations and the strongly
reflective, untectonized western volcano together with the volcanic
character of the seismic record provided evidence that lava erupted on
the East Gakkel Ridge within days to months prior to a May 1999
submarine survey (Edwards et al., 2001). Because 12-kHz sonars can
penetrate through thin sediments covering acoustically reflective
lavas, it is possible that no eruption occurred on Gakkel Ridge in
1999. Historical global seismic records indicate that this was the
only earthquake swarm detected on the Gakkel Ridge in about 100 years.
Information Contacts: Oceanus: The Online Magazine of Research from
Woods Hole Oceanographic Institution (URL:
http://www.whoi.edu/oceanus/).
Ol Doinyo Lengai
Tanzania
2.764°S, 35.914°E; summit elev. 2,962 m
All times are local (= UTC + 3 hours)
This report chiefly discusses observations made at Ol Doinyo Lengai
(hereafter called Lengai) in the first half of 2009. Broadly speaking,
the active N crater continued to be the scene of venting. More
specifically, the cone that covers much of what was the N crater
contained a steep-sided crater with a tight cluster of active hornitos
and spatter cones on its floor. Conditions during 2009 visits were
generally calm, although minor eruptions on the crater floor
continued. This is in contrast to explosive eruptions during September
2007-March 2008 (BGVN 32:11, 33:02, 33:06, 33:08, 34:02).
In the late stages of preparing this issue we received a report from
Tobias Fischer stating that when he and his team visited on 11-12 June
2009, one side of the crater contained a convecting lava lake. That
report will appear in our next issue.
Most of the groups that arrived at Lengai in 2009 did not ascend to
the active crater and the SE route remained difficult. Gas samples
collected here in 2005 were published and interpreted in Fischer and
others (2009). The next subsection confirms original interpretations
of a 2007 satellite image.
September 2007 ASTER image. David Sherrod was among USGS visitors
during January 2009, working with local government officials and
studying tephra deposits from explosive eruptions during September
2007-March 2008 that were distributed well out from the volcano (BGVN
34:02). When commenting about the cause of the large lobate black
areas on Lengai's NW, W, and E sides seen in ASTER imagery from 4
September 2007 (BGVN 32:11) he noted, "the lava flows of late
2007-early 2008 are far more restricted than the blackened areas
visible on the photos."
This is in agreement with the statement by Roger Mitchel in the
original discussion (and the original figure caption). Sherrod also
said, "I'm fairly certain [the dark lobes] are burn areas. The fires
can be natural, but they are also set by herdsman to improve access
and grass quality. The dark areas show on many past images, including
those from times in the absence of eruptions. They commonly have
well-defined margins and thorough coverage within. Lava flows have
well defined margins but more erratic coverage within the bounds,
creating digitate lobes."
Comments on aviation hazards during 2007-2008. Comparatively few
pictures or comments on aviation hazards have emerged from the recent
episode of Plinian eruptions during 2007-2008. Ben Wilhelmi took a
series of photos of the ground surface at distance from the volcano
during a week in November 2007. From the air he saw ash as far away as
70 km from the volcano, including in many cases, over Masai villages
that dot the landscape.
Wilhelmi's discussion and photos follows. "[During] 2007 and 2008 ...
smoke and ashes sometimes [rose] up to 50,000 ft, 15 km high. It
looked like a Hiroshima mushroom [cloud (figure 8)]. Here is ash
deposit on my aircraft [(figure 9)]. Often the ash was invisible in
the air though. [Three] turbine engines died in different companies
because of ash intakes. It happened one of these engines [died] on me.
Luckily I could finish the flight, but I didn't like the feeling to
see the engine temperature in the red and [flying] on reduced power.
Figure 8. A tall (roughly 15-17 km altitude) Ol Doinyo Lengai plume
from the 2007-2008 eruptive interval taken at unstated date and
directional bearing. Short burst of lightning were visible in the
plume but were not captured in this photo. Courtesy of Ben Wilhelmi.
Figure 9. Two photos of Ol Doinyo Lengai ash deposits on leading
surfaces of a small propeller-driven airplane from encounter with ash
while in flight. Photographer and pilot Ben Wilhelmi commented that
the ash was often invisible during the encounter.
"In other countries, such an activity [as seen in figure 8] would have
imposed the area to be closed within 200 miles [~ 320 km], that would
have included Arusha and all the Serengeti [and] Ngorongoro [park and
conservation areas]. "Competent" authorities were asleep, the regional
companies happily kept on flying ... and subsequently lost 3 engines
as I've said earlier. Costs could go up to $350,000 for a new turbine
engine ... I certainly didn't complain as I could shoot [photos at
will and] got to see incredible spectacles like this day with a 55,000
ft or 17 km high plume of smoke with an electric thunderstorm inside!"
February 2009 visit. Anatoly Zaitsev and Gregor Markl reported that in
mid-February 2009 a group from St. Petersburg, Russia (A.N. Zaitsev,
S.V. Petrov, T.A. Golovina, and E.O. Zaitseva) and Tuebingen, Germany
(G. Markl and T. Wenzel) climbed the volcano. There were no ash or gas
emissions during the visit, although on the crater floor lava bubbled
and spattered.
The group reached the summit around 0830 on 18 February after ~ 4.5
hours of climbing. They ascended along the traditional W route (an
approach enabling rapid access but potentially exposing climbers to
eruptive debris). They stayed on the summit and in the N crater for ~
5 hours. On the large cone in the N crater they walked around the
active crater's rim on the W, S, and E sides (figure 10). They crossed
the depression between the two rims on the S side of the cone, the
outer rim belonging to an earlier stage of development, the inner rim
lying along the margin of the current crater. In that depression they
found meter-sized blocks (figure 11).
Figure 10. Ol Doinyo Lengai's active crater as seen looking W along
the rim. The crater resides in the cone that grew in the N crater in
the past few years. Photo taken 18 February 2008. Courtesy of Sergey
Petrov.
Figure 11. Large blocks found in the depression along the S upland
portion of the active cone in Ol Doinyo Lengai's N crater. Note field
gear for scale (right foreground). Photo courtesy of Tamara Golovina.
Three hornitos (spatter cones) were observed deep in the crater floor.
One, with a broken upper part, was active throughout the visit. Inside
that hornito they saw bubbling lava, and several times black spatter
was ejected.
The surface of the cone around the deep pit crater's rim consisted of
gray fine-grained ash with rare blocks of ejected silicate rocks.
Later analysis of a sample taken from the surface of the cone using
X-ray diffraction indicated significant amounts of calcite in addition
to silicate minerals. The depression between the rims of a new and old
craters was covered by numerous blocks and bombs of silicate rocks
(nephelinites, wollastonite nephelinites, and ijolites) and partly
altered natrocarbonatites.
Fumarolic activity in the northern crater was weak. The group observed
just a few small cracks emitting gases that were relatively
cold-probably less than 100°C.
Summary of 2009 visits. Table 3 shows a list of observers known to
have visited or flown over Lengai since 2009 began. Available photos
and text indicate that on the crater floor, hornitos continued to
spatter lava. Otherwise, relative calm was seen, typically even devoid
of steam, during much of the interval 1 October 2008 through 25 April
2009.
Table 3. Summary of selected observations describing Ol Doinyo Lengai
during January-April 2009. Courtesy of Ben Wilhelmi and Frederick
Belton.
Dates Observer(s) Brief observation(s) (CV=climbed volcano;
F=flank observations; A=aerial observations/photos from crater
overflight)
18-22 Jan 2009 Representatives from the U.S. Geological Survey,
U.S. Agency for International Development, Geological Survey of
Tanzania, and Tanzania Prime Minister's Office. (F) See BGVN 34:02
18 Feb 2009 A.N. Zaitsev, S.V. Petrov, T.A. Golovina, E.O.
Zaitseva, G. Markl, and T. Wenzel (CV) See text above
14 Mar 2009 Stefan Lubben (CV) Climbed through the Pearly Gates
without difficulty. At summit, they smelled sulfur but heard nothing
from the volcano.
07 Apr 2009 Alexander Daneel (A, figure 12) Photos indicate
small cones on the crater floor in similar spots to those seen active
by H. Loubieres and F. Vignes on 1 September 2008 (BGVN 33:08). This
lack of change suggests only minor volcanism from the crater during 1
September 2008 to 7 April 2009.
25 Apr 2009 Ben Wilhelmi (A, figure 13) Photos showing numerous
hornitos with spatter widespread on the crater floor and in places on
the crater walls.
Regarding his March visit to the summit, Stefan Lubben reported that
amid wet and windy weather they could smell sulfur. But they heard
nothing from the volcano.
On 7 April 2009 Alexander Daneel photographed the summit crater from
the air (figure 12). Some of the same small lava cones inside the
crater were seen to be active by Herve Loubieres and Francoise Vignes
on 1 September 2008. An aerial view on 25 April showed numerous
hornitos that had formed in the previous 4-5 months (figure 13).
Figure 12. Aerial view on 7 April 2009 looking SW across the Ol Doinyo
Lengai crater. On the rim's E side there is a small slump (at left).
Courtesy of Alexander Daneel.
Figure 13. Aerial photo of Ol Doinyo Lengai's crater floor taken on 25
April 2009 with uncertain orientation with respect to N. The floor
contains numerous hornitos. According to the pilot and photographer,
Ben Wilhelmi, who often flies over for observations, these features
probably formed during the previous 4-5 months. Courtesy of Ben
Wilhelmi.
Gas chemistry. Based on chemical analyses of gas samples collected by
Bernard Marty in July 2005 (BGVN 30:10) (figure 14), Fischer and
others (2009) reported that a very small amount of melting of Earth's
mantle, akin to that beneath mid-ocean ridges, can produce
carbonatites. Their gas samples, containing minimal air contamination,
revealed that the carbon dioxide came from the upper mantle below the
East African Rift.
Figure 14. Collecting volcanic gas samples at Ol Doinyo Lengai's
active crater in 2005 (Fisher, 2009). Courtesy of Tobias Fischer,
University of New Mexico.
Fischer and others (2009) state, "On a global scale, our results imply
that the regions of upper mantle beneath mid-ocean ridges, continental
North America, and the East African Rift were identical in their
volatile abundances and isotopic compositions. Despite small
differences in some trace gases (for example Xe isotopes in
MORBs-mid-ocean ridge basalts-versus [gases from continental wells]),
the upper mantle appears to be a uniform and homogenous geochemical
reservoir of CO2 and other gases (N2, He, and Ar) below both
continent[s] and oceans."
Reference: Fischer, T.P., Burnard, P., Marty, B., Hilton, D.R., Furi,
E., Palhol, F., Sharp, Z.D., and Mangasini, F., 2009, Upper-mantle
volatile chemistry at Oldoinyo Lengai volcano and the origin of
carbonatites, Nature, v. 459, p. 77-80 (doi:10.1038/nature07977).
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 to the Maasai as "The
Mountain of God," rises abruptly above the broad plain south of Lake
Natron in the Gregory Rift Valley. The cone-building stage of the
volcano ended about 15,000 years ago and was followed by periodic
ejection of natrocarbonatitic 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 and occasionally down the upper flanks. The
depth and morphology of the northern crater have changed dramatically
during the course of historical eruptions, ranging from steep crater
walls about 200 m deep in the mid-20th century to shallow platforms
mostly filling the crater. Long-term lava effusion in the summit
crater beginning in 1983 had by the turn of the century mostly filled
the northern crater; by late 1998 lava had begun overflowing the
crater rim.
USGS, Vancouver, WA, USA; Anatoly Zaitsev, St. Petersburg State
University, Saint Petersburg, Russia; Gregor Markl, Tuebingen,
Germany; Frederick Belton, Developmental Studies Department, PO Box
16, Middle Tennessee State University, Murfreesboro, TN 37132, USA
(URL: http://frank.mtsu.edu/~fbelton/lengai.html;
http://www.oldoinyolengai.org/); Ben Wilhelmi (URL:
http://www.benwilhelmi.com/;
http://benwilhelmi.typepad.com/benwilhelmi/).
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