Krakatoa: The 1883 Eruption

Background Information

· Krakatau in Bahasa Indonesia

· Volcanic island formed by subduction of Indo-Australian plate under Eurasian plate

· Part of the Indonesian island arc system

· In the Sunda Strait between Java and Sumatra

· Originally (pre-1883) a 9km-long island

· Activity since 1927 created a new island, Anak Krakatoa (Child of Krakatoa)

Short Term Effect

-The former volcanic cones of Perboewatan and Danan fell into a hole in the crust which flooded with seawater. Only the southern part of Rakata remained. 2/3 of the original island was destroyed.

-Paroxysmal volcanic explosions, submarine landslides and the atmospheric shockwaves from the eruption caused tsunami waves which reached heights of 20-30m and speeds up to 600mph.

-Tsunami waves caused most of the casualties, wiping out entire coastal villages and towns and coral reefs.

-Death toll was estimated at 36000.

-Pumice and ash rained from the sky, pelting the decks of ships, threatening to sink them.

-Sound of the eruption was loud enough to break the eardrums of sailors miles away.

-'Blood red' sunsets phenomenon caused by dust blown into the high atmosphere.

Long Term Effect

-Volcanic dust released blocks a proportion of the incoming solar radiation, reducing temperatures on the Earth’s surface.

-After the Krakatau eruption, several years of poor summers and harsh winters followed as a result of this effect. Global temperatures lowered as much as 1/2 degree centigrade for five years.

-Volcanic dust and aerosols block sunlight, causing the ocean’s surface to cool and recede, temporarily offsetting rising sea levels due to global warming.

Possible Causes

· Some theories speculate that when the walls of the volcano ruptured, seawater rushed in to the magma chamber and created super-heated steam, which caused the large explosions. These are called phreatic eruptions:

- Magma heats water

- Water evaporates into steam nearly instantly

- Sudden expansion of volume

- Explosion of steam, water, ash, rock, volcanic bombs

· Seawater may have cooled the magma and caused it to crust over, enclosing the chamber and thus allowing pressure to build up that ultimately led to an explosion.

Current actions taken to monitor Krakatoa

1. The PVMBG specialists who are guarding the volcano are saying however that a violent eruption generating a tsunami is highly unlikely at this alert level (krakatau is an island and a huge part of the volcano is below sea level).

2. Many coastal villages in the Sunda strait fear that this volcano with a violent past will explode again. Scientists can predict volcano eruptions fairly well today

3. GPS recordings which show an eventual deformation of parts of the volcano are giving a good hint in the potential danger

4. Inhabitants of coastal villages have been told by the scientists that they should calm down because a major eruption like the 1883 is highly unlikely at the this moment


· People have been notified of evacuation plans

· Education to the people there about preventing themselves from danger