Indonesia has seen other catastrophic volcanic eruptions in addition to Tambora. The island nation of indonesia has more volcanoes than any other country in the world, with more than 130 known active volcanoes in this island-continental margin-arc system. These volcanoes have been responsible for about one-third of all the deaths attributed to volcanic eruptions in the world. indonesia stretches for more than 3,000 miles (5,000 km) between southeast Asia and Australia and is characterized by fertile soils and warm climates. it is one of the most densely populated places on Earth. its main islands include, from Northwest to southeast, sumatra, Java, Kalimantan (formerly Borneo), sulawesi (formerly Celebes), and the sunda islands. The country averages one volcanic eruption per month; because of the dense population, indonesia suffers from approximately one-third of the world's fatalities from volcanic eruptions.
one of the most spectacular and devastating eruptions of all time was that of 1883 from Krakatau, an uninhabited island in the sunda strait off the coast of the islands of Java and sumatra. This eruption generated a sonic blast heard thousands of miles away, spewed enormous quantities of ash into the atmosphere, and initiated a huge tsunami that killed roughly 40,000 people and wiped out more than 160 towns. The main eruption lasted for three days, and the huge amounts of ash ejected into the atmosphere circled the globe, remained in the atmosphere for more than three years, forming spectacular sunsets and affecting global climate. Locally the ash covered nearby islands, killing crops, natural jungle vegetation, and wildlife, but most natural species returned within a few years.
Like Tambora, Krakatau is located at an anomalous location in the indonesian arc. To the southeast of Krakatau, the volcanoes on the island of Java are aligned in an east-west direction, lying above the subducting indo-Australian plate. To the northwest of Krakatau volcanoes on sumatra are aligned in a northwest-southeast direction. Krakatau is thus located at a major bend in the indonesian arc and lies along with a few other smaller volcanoes above the Krakatau fault zone that strikes through the sunda strait. This fault zone is accommodating differential motion between Java and sumatra. Java is moving east at 1.5 inches (4 cm per year), whereas sumatra is moving northeast at 1.5 inches (4 cm per year) and rotating in a clockwise sense, resulting in a zone of oblique extension along the Krakatau fault zone in the sunda strait. The faults and fractures formed from this differential motion between the islands provide easy pathways for the magma and other fluids to migrate from great depths above the subduction zone to the surface. so like Tambora, Krakatau has had unusually large volcanic eruptions and is located at an anomalous structural setting in the indonesian arc.
Legends in the indonesian islands speak of several huge eruptions from the sunda strait area, and geological investigations confirm many deposits and calderas from ancient events. Before the 1883 eruption Krakatau consisted of several different islands including Perbuwatan in the north, and Danan and Rakata in the south. The 1883 eruption emptied a large underground magma chamber and formed a large caldera complex. During the 1883 eruption Per-buwatan, Danan, and half of Rakata collapsed into the caldera and sank below sea level. since then a resurgent dome has grown out of the caldera, emerging above sea level as a new island in 1927. The new island, named Anak Krakatau (child of Krakatau), is growing to repeat the cycle of cataclysmic eruptions in the sunda strait.
Before the 1883 eruption the sunda strait was densely populated with many small villages built from bamboo with palm-thatched roofs, and other local materials. Krakatau is located in the middle of the strait, with many arms of the strait extending radially away into the islands of sumatra and Java. Many villages, such as Telok Betong, lay at the ends of these progressively narrowing bays, pointed directly at Krakatau. These villages were popular with trading ships from the indian ocean which stopped to obtain supplies before heading through the sunda strait to the East indies. The group of islands centered on Krakatau in the middle of the strait was a familiar landmark for these sailors.
Although not widely appreciated as such at the time, the first signs that Krakatau was not a dormant volcano but was about to become very active appeared in 1860 and 1861 with small eruptions, then a series of earthquakes between 1877 and 1880. on may 20, 1883, Krakatau entered a violent eruption phase, witnessed by ships sailing through the sunda strait. The initial eruption sent a seven-mile (11-km) high plume above the strait, with the eruption heard 100 miles (160 km) away in Jakarta. As the eruption expanded, ash covered villages in a 40-mile (60-km) radius. For several months the volcano continued to erupt sporadically, covering the straits and surrounding villages with ash and pumice, while the earthquakes continued.
on August 26, the form of the eruptions took a severe turn for the worse. A series of extremely explosive eruptions sent an ash column 15 miles (25
km) into the atmosphere, sending many pyroclastic flows and nuées ardentes spilling down the island slopes and into the sea. Tsunamis associated with the flows and earthquakes sent waves into the coastal areas surrounding the Sunda Strait, destroying or damaging many villages on Sumatra and Java. Ships passing through the straits were covered with ash, while others were washed ashore and shipwrecked by the many and increasingly large tsunamis.
On August 27, Krakatau put on its final show, exploding with a massive eruption that pulverized the island and sent an eruption column 25 miles (40 km) into the atmosphere. The blasts from the eruption were heard as far away as Australia, the Philippines, and Sri Lanka. Atmospheric pressure waves broke windows on surrounding islands and traveled around the world as many as seven times, reaching the antipode (area on the exactly opposite side of the Earth from the eruption) at Bogatâ, Colombia, 19 hours after the eruption. The amount of lava and debris erupted is estimated at 18-20 cubic miles (75-80 km3), making this one of the largest eruptions known in the past several centuries. Many sections of the volcano collapsed into the sea, forming steep-walled escarpments cutting through the volcanic core, some of which are preserved to this day. These massive landslides were related to the collapse of the caldera beneath Krakatau and contributed to huge tsunamis that ravaged the shores of the Sunda Strait, with average heights of 50 feet (15 m), but reaching up to 140 feet (40 m) where the V-shaped bays amplified wave height. Many of the small villages were swept away with no trace, boats were swept miles inland or ripped from their moorings, and thousands of residents perished in isolated villages in the Sunda Strait.
Although it is uncertain how many people died in the volcanic eruption and associated tsunamis, the Dutch colonial government estimated in 1883 that 36,417 people died, with most of these deaths (perhaps 90 percent) from the tsunami. Several thousand people were also killed by extremely powerful nuées ardentes, or glowing clouds of hot ash that raced across the Sunda Strait on cushions of hot air and steam. These clouds burned and suffocated all who were unfortunate enough to be in their direct paths.
Tsunamis from the eruption spread out across the Indian Ocean and caused destruction along much of the coastal regions of the entire Indian Ocean, eventually moving around the world. Although documentation of this Indonesian tsunami is not nearly as good as that from the 2004 tsunami, many reports of the tsunami generated from Krakatau document this event. Residents of coastal India reported the sea suddenly receding to unprecedented levels, stranding fish that were quickly picked up by residents, many of whom were then washed away by large waves. The waves spread into the Atlantic Ocean and were detected in France, and a seven-foot (2-m) high tsunami beached fishing vessels in Auckland, New Zealand.
Weeks after the eruption huge floating piles of debris and bodies were still floating in the Sunda Strait, Java Strait, and Indian Ocean, providing grim reminders of the disaster to sailors in the area. Some areas were so densely packed with debris that sailors reported those regions looked like solid ground, and one could walk across the surface. Fields of pumice from Krakatau reportedly washed up on the shores of Africa a year after the eruption, some mixed with human skeletal remains. Other pumice rafts carried live plant seeds and species to distant shores, introducing exotic species across oceans that normally acted as barriers to plant migration.
Ash from the eruption fell more than 1,500 miles (2,500 km) from the eruption for days after it, and many fine particles remained in the atmosphere for years, spreading across the globe by atmospheric currents. The ash and sulfur dioxide from the eruption caused a lowering of global temperatures by several degrees and created spectacular sunsets and atmospheric light phenomena by reflected and refracted sunlight through the particles and gas emitted into the atmosphere.
On western Java, one of the most densely populated regions in the world, destruction on the Ujong Kulon Peninsula was so intense that it was designated a national park, as a reminder of the power and continued potential for destruction from Krakatau. Such designations of hazardous coastal regions and other areas of potential destruction as national parks and monuments is good practice for decreasing the severity of future natural eruptions and processes.
Krakatau began rebuilding new cinder cones that emerged from beneath the waves in 1927 through 1929, when the new island, Anak Krakatau (child of Krakatau), went into a rapid growth phase. Several cinder cones have now risen to heights approaching 600 feet (190 m) above sea level. The cinder cones will undoubtedly continue to grow until Krakatau's next catastrophic caldera collapse eruption.
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