Saturday 29 December 2018

INDONESIA: Anak Krakatoa's Crater Reduced By Three-quarters After Tsunami Eruption

The Indonesian volcano which caused a tsunami that killed more than 400 people last week lost more than two-thirds of its height following the eruption which triggered the killer waves.

A section of Anak Krakatoa's crater collapsed after an eruption and slid into the ocean, generating the tsunami last Saturday night.

A visual analysis by the Indonesian volcanology agency found the volcano has lost more than two-thirds of its height, an official said Saturday.

Anak Krakatoa which used to stand 338 metres (1,109 feet) high was now just 110 metres tall.

The agency estimated the volcano lost between 150 and 180 million cubic metres of material as massive amounts of rock and ash have been slowly sliding into the sea following a series of eruptions.

Anak Krakatoa is now much shorter, usually you can see the peak from the observatory post, now you can't, Wawan Irawan, a senior official at the agency said.

Before and after satellite images taken by Japan's space agency showed that a two square kilometre chunk of the volcanic island had collapsed into the water.

The volcano, whose name means Child of Krakatoa, was a new island that emerged around 1928 in the crater left by Krakatoa, whose massive 1883 eruption killed at least 36,000 people.

The crater's status has been raised to high alert, the second-highest warning on Indonesia four-point danger scale.

The exclusion zone has been extended from two to five kilometres (1.2 to three miles).

A week after the tsunami, thousands of Indonesian Muslims attended a mass prayer on Saturday to remember the victims and pray for the safety of their tsunami-prone hometown.

Residents of Pandeglang regency, which was hit the hardest by the disaster, gathered in the early morning, some in tears as they chanted their prayers.

I prayed for the victims and I also pray for the safety of the people who live in the tsunami affected area,a tsunami survivor said.

My prayer is for the victims to get help and be granted patience and I also pray the government will immediately help us to rebuild, to provide clothes and food, or at least to give us moral support, a survivor said.

Authorities said at least 426 people were killed and 23 missing in the disaster.

Some 7,202 people suffered injuries and nearly 1,300 homes were destroyed after the waves crashed into the coastlines of western Java island and south Sumatra.

More than 40,000 people have been evacuated for fear of another tsunami as Anak Krakatoa continues to rumble.

Indonesia, a vast Southeast Asian archipelago, is one of the most disaster-hit nations on Earth due to its position straddling the so-called Pacific Ring of Fire, where tectonic plates collide.

Krakatoa, or Krakatau, is a volcanic island situated in the Sunda Strait between the islands of Java and Sumatra in the Indonesian province of Lampung.

The name is also used for the surrounding island group comprising the remnants of a much larger island of three volcanic peaks which were obliterated in a cataclysmic 1883 eruption. The entire edifice is a stratovolcano.

In 1927, a new island, Anak Krakatau, or "Child of Krakatoa", emerged from the caldera formed in 1883. It is the current location of eruptive activity.

The most notable eruptions of Krakatoa culminated in a series of massive explosions over 26–27 August 1883, which were among the most violent volcanic events in recorded history.

With an estimated Volcanic Explosivity Index (VEI) of 6, the eruption was equivalent to 200 megatons of TNT (840 PJ)—about 13,000 times the nuclear yield of the Little Boy bomb (13 to 16 kt) that devastated Hiroshima, Japan, during World War II, and four times the yield of Tsar Bomba (50 Mt), the most powerful nuclear device ever detonated.

The 1883 eruption ejected approximately 25 km3 (6 cubic miles) of rock. The cataclysmic explosion was heard 3,600 km (2,200 mi) away in Alice Springs, as well as on the island of Rodrigues near Mauritius, 4,780 km (2,970 mi) to the west.

According to the official records of the Dutch East Indies colony, 165 villages and towns were destroyed near Krakatoa, and 132 were seriously damaged.

At least 36,417 people died, and many more thousands were injured, mostly from the tsunamis that followed the explosion. The eruption destroyed two-thirds of the island of Krakatoa.

Eruptions in the area since 1927 have built a new island at the same location, named Anak Krakatau which is Indonesian for "Child of Krakatoa".

Periodic eruptions have continued since, with recent eruptions in 2009, 2010, 2011, and 2012. In late 2011, this island had a radius of roughly 2 kilometres (1.2 mi), and a highest point of about 324 metres (1,063 ft) above sea level, growing 5 metres (16 ft) each year.

In 2017 the height of Anak Krakatau was reported as over 400 metres above sea level. However, due to the recent eruption in December 2018, the height has been reduced to 110 meters (361 ft).

Indonesia has over 130 active volcanoes, the most of any nation. They make up the axis of the Indonesian island arc system produced by northeastward subduction of the Indo-Australian Plate.

A majority of these volcanoes lie along Indonesia's two largest islands, Java and Sumatra. These two islands are separated by the Sunda Strait located at a bend in the axis of the island arc.

Krakatau is directly above the subduction zone of the Eurasian Plate and the Indo-Australian Plate where the plate boundaries make a sharp change of direction, possibly resulting in an unusually weak crust in the region.

Tourism Observer

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