krakatau history -vulcanic active

apud saepudin — Thu, 02 Jun 2011 12:59:12 GMT

Volcanic activity recommenced in May, 1883 and continued into August, the first eruptions appearing on the northern, Perbuatan volcano. The number of active vents increased on both the northern volcanoes. On the 26 th and 27 th August series of cataclysmic explosions occurred which were heard 3500 miles away as far away as South Australia and Ceylon, was recorded as of the world's biggest explosion the force of 100.000 hydrogen bombs, They generated tsunamis (tidal wave) crashed ashore and devastated hundreds of town and village, reaching almost 10 miles inland in some places. The resulting killer waves at speed up to a 350 miles per hour and reached height of 135 feet that were registered even in the English Channel , 11.000 miles away and which in the Sunda - strait area were devastating, killing more than 36.000 people. That total volume of material ejected by the eruption is estimated at some 18 - 21 cubic kilometers, 30 km high into the atmosphere with an ash cloud circling the earth several times. Causing "blue suns" and "orange moons" Europe and North America . The amount of the sun's energy reaching the earth was reduced, and in the year or two that followed, annual average temperatures in the northern hemisphere were than usual.

In the aftermath of the explosion only about a third of Krakatau remained. The northern two thirds, including the volcanoes Perbutan and Danan and the northern half of the Rakata Volcano, were gone. In their place was a collapsed crater (caldera) 200m beneath the sea, covering an area of about 28 square kilometer. The remaining, southern part of Rakata was left as approximate half, cone with an almost perpendicular cliff from the summit (813 m) to the sea, providing a natural, geological section through the volcano. The other two islands, Sertung and Panjang, were enlarged considerably (Sertung doubled in size) by the glowing ash and pumice which smothered them to a depth of 30 meters. On Rakata, the south and west coasts were were extended almost a kilometer-seawards and the ash layer reached a thickness of 60 m in some areas, although probably much shallower on the steeper slopes. Weeks after the explosion, rain water turned into steam as it trickled into crevices and a even month later the surface was too hot for bare feet. It is believed that all life, plant and animal, was destroyed on the islands. Yet the three islands are now covered in forest, and over 200 species of higher plants and 36 species of land birds have been found on Rakata in the 1980s.

At some point in the distant past, Krakatau consisted of a single, large volcanic island. This island was destroyed in eruptions presumably of great violence, leaving three fragments of the original volcanic walls in a broken ring, or caldera, around the edge of this original island. The three islands are now named Rakata, Sertung and Panjang. Subsequently, further eruptions began, building up the largest island (Rakata) back into the center of the caldera. As of 1883, the only previous recorded eruptions had come from this big island in 1680. The islands of Panjang and Sertung, then as now, remained dormant. Then in May of 1883, eruptions began again on the big island, and one by one, the three peaks of the island -- Perboewatan, Danan and Rakata -- each came into action as the cycle of building and destruction reached its peak. Finally, on August 27th, the sequence ended in catastrophe, as huge volumes of ejecta were hurled into the sky, plunging the surrounding region for a radius of 80 km into 57 hours of darkness. Relatively few people appear to have died as a direct result of the ejecta, but huge numbers died because of an indirect consequence of the eruption. As the magma chamber emptied, the outer walls of the volcano failed, and collapsed -- repeating the pre-historic caldera collapse -- displacing two-thirds of the island.

These events generated a series of giant waves, or tsunami, which steepened as they reached shallow waters. Lava forming islandsThese waves swept across the coastal lowlands of Java and Sumatra on either side of the Sunda Strait, killing an estimated 36,000 people and destroying many settlements. As an illustration of the forces involved, a government gunboat, the Berouw, was carried nearly 3 km inland and stranded behind a small hill 9 m above sea-level (the crew of 28 were amongst those who died). The violence ended abruptly, leaving a greatly re-shaped archipelago. In the centre of the caldera, where there had once been a substantial island, the sea-floor was reached at a depth of over 250 m. The three remaining islands were greatly re-shaped, and in places extensive new land surfaces had been created by the deposition of great thicknesses of pyroclastic ashes where once had been nothing but the sea. On the persisting areas of land, an average of 60-80 m of these ashes had been emplaced. The resulting landscapes were completely barren, and as far as can be established, no life survived. Plants and animals soon colonized, and the ecosystem re-building began -- a story we will come back to. Down in the depths of the earth, the emptied magma chamber will, once again, have begun to fill, eventually creating sufficient pressure to begin the construction phase of the cycle once again, naturally, pretty much in the center of the caldera

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krakatau history -vulcanic active