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VolcanoWatch Weekly [16 September 2009]

Posted by feww on September 17, 2009

VOW: Krakatoa [Krakatau]

Krakatoa is a volcanic island in the Sunda Strait located between Indonesian islands of Java and Sumatra. Both the volcano and island group share the same name.

Four enormous explosions almost entirely destroyed Krakatoa island on August 27, 1883. The violent explosions were reportedly heard in Perth, Western Australia,  some 3,500 km away. It was heard even on the island of Rodrigues near Mauritius, about 4,800 km away.

The shockwave from the last explosion, which ejected volcanic matter 80 km into the atmosphere, echoed around the planet seven times.

Karakatoa
An 1888 lithograph of the 1883 violent explosion of Krakatoa.

The eruption ejected about 21 cubic kilometers of volcanic matter and completely destroyed two-thirds of the Krakatoa island.

island map
The Island Map (Simkin and Fiske, 1983). Image may be subject to copyright.

Anak Krakatau (the Child of Krakatau)  is the only active vent left from Krakatoa. u is  This volcano has built itself slowly from the sea floor since the paroxysmal eruption of 1883.  Anak Krakatau is located between the northern two vents, Danan and Perboewatan, that were destroyed in the 1883 eruption.  For the most part, the eruptions are Vulcanian, slowly building the island with a combination of lava, ash, and pumice.

location map
Krakatoa: Location Map. Source of the original map: USGS

Krakatoa_01
Krakatoa: An early 19th Century image.

Early in the morning of May 20, 1883, the captain of the German warship Elizabeth reported seeing an ~11-km-high cloud of ash and dust rising above the uninhabited island of Krakatau, thus documenting the first eruption from this Indonesian island in at least two centuries. Over the ensuing two months, crews on commercial vessels and sightseers on charted ships would experience similar spectacles, all of which were associated with explosive noises and churning clouds of black to incandescent ash and pumice. From a distance, the largest of these natural fanfares impressed the local inhabitants on the coastal plains of Java and Sumatra, creating a near-festive environment. Little did they realize, however, that these awe-inspiring displays were only a prelude to one of the largest eruptions in historic times. A series of cataclysmic explosions began at mid-day on August 26, and ended on August 27 with a stupendous paroxysmal eruption. On this day, the northern two-thirds of the island collapsed beneath the sea, generating a series of devastating pyroclastic flows and immense tsunamis that ravaged adjacent coastlines. The events that began on August 26 would mark the last 24 hours on earth for over 36,000 people [possibly as many as 120,000,] and the destruction of hundreds of coastal villages and towns. —Geology-/SDSU [Spelling mistakes corrected by FEWW.]

ashcroft -riv thames
William Ashcroft painting “On the Banks of the River Thames” in London, November 26, 1883 [Exactly three months after Krakatoa’s cataclysmic 1883 eruption.]

The Krakatoa eruption affected the climate driving the weather patterns wild for the next 5 years. Average global temperatures fell by about 1.2 °C in the following years, returning to normal only in 1888.

landsat PP1
Krakatoa Image by Landsat Pathfinder Project (Dated May 18, 1992)

Anak Krakatau’s most recent eruptive episode began in 1994, with near continuous Strombolian eruptions, punctuated by larger explosions.  In its most recent eruption, which began in April 2008, the volcano released hot gases, rocks, and lava. Scientists monitoring the volcano have warned people to stay out of a 3 km zone around the island. By and large, the eruptions are Vulcanian, helping to slowly build the island with ash, lava and pumice at an average rate of about 60 cm per month.

Fearing an imminent eruption, Volcanological Survey of Indonesia raised Anak’s  eruption alert level to Orange on May 6, 2009.

SI /USGS Weekly Volcanic Activity Report
(9 September – 15 September 2009)

New activity/unrest:

News From GVP:

  • PHIVOLCS reported that 11 earthquakes from Mayon were detected during 14-15 September. On 15 September, three ash explosions produced a brownish plume that rose no more than 700 m above the crater and drifted SW.
  • On 11 September, KVERT reported strong explosions from Shiveluch. Based on interpretations of seismic data, ash plumes rose to an altitude greater than 15 km (49,200 ft) a.s.l. The seismic network then detected eight minutes of pyroclastic flows from the lava dome; resulting plumes rose to an altitude of approximately 10 km (32,800 ft) a.s.l. —GVP

Tafu-Maka


A bathymetric map prepared during a NOAA Vents Program November 2008 expedition shows two submarine volcanoes, Tafu (Tongan for “source of fire”) and Maka (Tongan for “rock”). The volcanoes lie along a NE-SW-trending ridge on the southern part of the back-arc NE Lau Spreading Center (NELSC). The November 2008 expedition discovered submarine hydrothermal plumes consistent with very recent (days to weeks?) submarine lava effusion from Maka volcano.  Image courtesy of NOAA Vents Program, 2008. Caption: GVP.

Ongoing Activity:


HAWAIIAN VOLCANO OBSERVATORY DAILY UPDATE

Wednesday, September 16, 2009 8:30 AM HST (Wednesday, September 16, 2009 18:30 UTC)

KILAUEA VOLCANO (CAVW #1302-01-)
19°25’16” N 155°17’13” W, Summit Elevation 4091 ft (1247 m)
Current Aviation Color Code: ORANGE
Current Volcano Alert Level: WATCH

Activity Summary for past 24 hours: The third DI event in a week started yesterday morning and switched to DI inflation overnight. Moderate glow was visible after dark from the Halema`uma`u Overlook vent (summit). Sulfur dioxide emission rates from the Halema`uma`u and east rift zone vents remain elevated. Lava from the TEB vent (east rift zone) flows through tubes to the ocean and feeds surface flows.

Past 24 hours at Kilauea summit:
Glow was visible from the Halema`uma`u Overlook vent overnight. This morning, trade winds are blowing the plume, denser than yesterday morning, to the southwest over the Ka`u Desert. The most recent sulfur dioxide emission rate measurement was 900 tonnes/day on September 11, which is well above the 2003-2007 average of 140 tonnes/day. Very small amounts of ash-sized rock dust waft up from the vent and are deposited nearby on the crater rim.

halema uma u
This Quicktime movie shows two active vents on the floor of the Halema`uma`u cavity. Lava is just below the rim of the two vents, creating frequent spattering which falls around their rims. Within the larger of the two (on the right), lava can be seen vigorously sloshing. For scale, these vents are about 10 yards wide. The first half of the movie is shown in normal mode, with the second half shown in ‘nightshot’ mode.

The summit tiltmeter network recorded the third DI event in a week with deflation just before 8 am yesterday and inflation just after midnight last night. The GPS network, which is less sensitive than the tiltmeter network, recorded less than 2 cm of contraction over the last 3 months with brief periods of extension coinciding with strong DI inflation on September 1-2 and 11-12; they recorded contraction since 9/13.

Seismic tremor levels remain elevated; two weak hybrid earthquakes followed by 15-20 minutes of sustained tremor were recorded starting around 7:30 pm last night. The number of RB2S2BL earthquakes continued to increase slightly but remained below background levels. Six earthquakes were recorded beneath Kilauea – three beneath the summit caldera, two deep quakes below the lower southwest rift zone, and one on south flank faults. —HVO

  • Videos and Images are available at: HVO

Related Links:

FEWW Volcanic Activity Forecast

Other Related Links:

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