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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 devasting 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, and the destruction of hundreds of coastal villages and towns.
ndonesia contains over 130 active volcanoes, more than any other country on earth. They comprise the axis of the Indonesian island arc system, which is generated by northeastward subduction of the Indo-Australian plate. The great majority of these volcanoes lie along the topographic crest of the arc's two largest islands - Java and Sumatra. The islands are separated by the Sunda Straits, which is located at a distinct bend in axis of the island arc volcanoes, from a nearly east-west orientation in Java to a northwest-southeast orientation in Sumatra. Krakatau is one of a several volcanic islands in the Sunda Straits located above an active north-northeast trending fault zone, an orientation quite distinct from the main island-arc trend. Although relatively small when compared to the largest volcanoes along the island arc, Krakatau and its associated volcanoes have shown the capacity to generate highly explosive eruptions.
Tuesday, August 25, 2009
krakatau ecotour
Overview
On August 27th, 1883 a series of blasts on the island of Krakatoa culminated in a colossal explosion that blew the island apart in one of the largest eruptions in recorded history. Below are a few brief facts about the blast and its effects.
1. The 23km square island of Krakatoa existed at a height of 450m above sea level. The blast leveled most of the island to 250m below sea level.
2. Pyroclastic flows traveled as far as 40km from the island consuming traversing ships in fire and ash.
3. The sound of the final explosion was heard over 4500km away and covered 1/13th of the Earth's surface.
4. The eruption generated tsunamis 40m high that devastated nearby coastlines.
5. The final death toll from pyroclastic flows, volcanic bombs, and tsunamis was calculated to be a devastating 36,417.
Geography and Geology
The island of Krakatoa is located in the Sundra Straits between the islands of Java and Sumatra off the southwestern coast of Indonesia. Krakatoa is one of many active volcanoes along the Indonesian Island Arc, including the famous Tambora volcano. This arc, containing over 130 active volcanoes, is produced by the subduction of the Indo-Australian plate as it moves northward towards mainland Asia.
The island of Krakatoa itself is lies next to two other islands: Lang and Verlaten. These three islands together are the remains of an ancient volcanic island. Ancient Krakatoa, as it is called, exploded in an enormous eruption around 416 A.D., according to Javanese scriptures. In that eruption the majority of the island collapsed into a 7km long caldera beneath Rakata on Krakatoa forming the three present day islands.
The map on the right shows Krakatoa as it was before the great eruption of 1833. Three major volcanoes existed on the island, Perboewetan, Danan(not shown but in the middle), and Rakata. Since the eruption and collapse of Ancient Krakatoa the chamber beneath these three volcanoes had begun to fill, heat up, and create enormous pressure. Of late, Perboewetan had been the most active.
On August 27th, 1883 a series of blasts on the island of Krakatoa culminated in a colossal explosion that blew the island apart in one of the largest eruptions in recorded history. Below are a few brief facts about the blast and its effects.
1. The 23km square island of Krakatoa existed at a height of 450m above sea level. The blast leveled most of the island to 250m below sea level.
2. Pyroclastic flows traveled as far as 40km from the island consuming traversing ships in fire and ash.
3. The sound of the final explosion was heard over 4500km away and covered 1/13th of the Earth's surface.
4. The eruption generated tsunamis 40m high that devastated nearby coastlines.
5. The final death toll from pyroclastic flows, volcanic bombs, and tsunamis was calculated to be a devastating 36,417.
Geography and Geology
The island of Krakatoa is located in the Sundra Straits between the islands of Java and Sumatra off the southwestern coast of Indonesia. Krakatoa is one of many active volcanoes along the Indonesian Island Arc, including the famous Tambora volcano. This arc, containing over 130 active volcanoes, is produced by the subduction of the Indo-Australian plate as it moves northward towards mainland Asia.
The island of Krakatoa itself is lies next to two other islands: Lang and Verlaten. These three islands together are the remains of an ancient volcanic island. Ancient Krakatoa, as it is called, exploded in an enormous eruption around 416 A.D., according to Javanese scriptures. In that eruption the majority of the island collapsed into a 7km long caldera beneath Rakata on Krakatoa forming the three present day islands.
The map on the right shows Krakatoa as it was before the great eruption of 1833. Three major volcanoes existed on the island, Perboewetan, Danan(not shown but in the middle), and Rakata. Since the eruption and collapse of Ancient Krakatoa the chamber beneath these three volcanoes had begun to fill, heat up, and create enormous pressure. Of late, Perboewetan had been the most active.
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