Volcano:

• a vent in the earth's crust through which lava, steam,

ashes, etc., are expelled, either continuously or at irregular

intervals.

Volcanic eruption:

• the sudden occurrence of a violent discharge of steam and

volcanic material

Types of volcanic eruptions:

Nineteenth century INDONESIA

KNOWN FOR ITS EXOTIC SPICES,THIS PART OF WORLD IS ABOUT TO BECOME FAMOUS FOR A VERY DIFFERENT REASON…..

…AS NEARBY RESIDENTS WITNESSED ONE OF THE LARGEST EXPLOSIONS EVER RECORDED

AUGUST 27,1883 10:02 AM

Unstable islands

The krakatoa islands sit above a volcanic hotspot on the pacific ring of fire. They may be remnants of a massive volcano that erupted and collapsed in ancient times, creating a giant water filled crater called a caldera

Eruption of krakatoa:• Location:

volcanic island located in the Sunda Strait between the islands of Sumatra and Java in Indonesia. This island is adjacent to two other islands, Verlaten and Lang.

• Events Leading up to the Explosion of Krakatoa:

minor eruptions from the Perboewetan volcano on the island of Krakatoa.there was an increase in ash fallout and chunks of pumice were found on the islands in the area. As these eruptions were occurring, the caldera on Perboewetan was widening and more pressure was building underwater.The first sizable blast of Krakatoa occurred in the early afternoon on August 26th, 1883. The volcano spewed a 15-mile high column of dark volcanic gas and it generated a shockwave which was felt in the neighbouring islands of Sumatra and Java. 

The Explosion of Krakatoa August 27th, 1883

• The first of four catastrophic explosions occurred at 5:30am on August 27th, 1883. An increasingly thick blanket of pumice and ash enveloped the neighbouring islands. Tsunamis of 100 feet high caused more damage along shorelines.

• The second blast occurred at 6:44am and it repeated the effects of the first blast.

• The third blast at 10:20am was the most intense of the four. Two-thirds of Krakatoa sunk into the caldera which was sitting at 750 feet below sea level.

• The last blast at 10:52am was not as intense but it perpetuated the damage.

• Eruptions

The biggest explosion of Krakatau occurred on August 26 and 27, 1883. Before the eruption the island was about 18 sq. miles. After the eruption the island was only 6 sq. miles. The eruption caused an earthquake which created tsunamis that reached more than 115 feet high and traveled some 8000 miles. The waves killed about 36,000 people on the nearby islands of Java and Sumatra, and destroyed 295 costal towns. The explosions produced some of the loudest noises in history.

Causes of karakatoa eruption:

• the volcano's vents had sunk below sea level on the morning of 27 August, letting seawater flood into it and causing a massive series of phreatic (interaction of ground water and magma) explosions.

• The seawater could have chilled the magma, causing it to crust over and producing a "pressure cooker" effect relieved only when explosive pressures were reached.

• A massive underwater land slump or partial subsidence suddenly left the highly pressurized magma chamber wide open.

• The final explosions may have been caused by magma mixing caused by a sudden infusion of hot basaltic magma into the cooler and lighter magma in the chamber below the volcano. This would have resulted in a rapid and unsustainable increase in pressure, leading to a cataclysmic explosion.

BEFORE AFTER

Local Effects of the Krakatoa Eruption

• Sailors on ships in nearby sea lanes reported astounding events associated with the volcanic eruption. The sound was loud enough to break the eardrums of some crewmen on ships many miles away. And pumice, or chunks of solidified lava, rained from the sky, pelting the ocean and the decks of ships.

• The tsunamis set off by the volcanic eruption rose as high as 120 feet, and slammed into the coastlines of the inhabited islands of Java and Sumatra. Entire settlements were wiped away, and it is estimated that 36,000 people died.

Distant Effects of the Krakatoa Eruption:

• The sound of the massive volcanic eruption traveled enormous distances across the ocean. At the British outpost on Diego Garcia, an island in the Indian Ocean more than 2,000 miles from Krakatoa, the sound was clearly heard. People in Australia also reported hearing the explosion. It is likely that Krakatoa created the loudest sound on earth.

• Pieces of pumice were light enough to float, and weeks after the eruption large pieces began drifting in with the tides along the coast of Madagascar, an island off the east coast of Africa. Some of the large pieces of volcanic rock had animal and human skeletons embedded in them.

Global climate effect:

• In the year following the eruption, average global temperatures fell by as much as 1.2 °C (2.2 °F). Weather patterns continued to be chaotic for years, and temperatures did not return to normal until 1888. The eruption injected an unusually large amount of sulfur dioxide (SO2) gas high into the stratosphere which was subsequently transported by high-level winds all over the planet. This led to a global increase insulfurous acid (H2SO3) concentration in high-level cirrus clouds. The resulting increase in cloud reflectivity (or albedo) would reflect more incoming light from the sun than usual, and cool the entire planet until the suspended sulfur fell to the ground as acid precipitation.

Global optical effects:• The eruption darkened the sky worldwide for years

afterwards, and produced spectacular sunsets throughout the world for many months. British artist William Ashcroft made thousands of colour sketches of the red sunsets half-way around the world from Krakatoa in the years after the eruption.

• Weather watchers of the time tracked and mapped the effects on the sky. They labeled the phenomenon the "equatorial smoke stream".

• This was the first identification of what is known today as the Jet stream.

• This eruption also produced a Bishop's Ring around the sun by day, and a volcanic purple light at twilight.

VOLCANO MITIGATION

Before the Disaster During the DisasterAfter the Disaster

• Learn about community warning systems and of disasters that can come from volcanoes (earthquakes, flooding, landslides, mudflows, thunderstorms, tsunamis)• Make evacuation plans to higher ground with a backup route• Get a pair of goggles and a throw-away breathing mask for each member of the household teach children how • Have disaster supplies on hand (flashlight, extra batteries, portable battery-operated radio, first aid kit, emergency food and water, nonelectric can opener, cash and credit cards, and sturdy shoes)• Develop an emergency communications plan in case of separation during the earthquake Ask an out-of-state relative or friend to serve as the family contact.

• Follow evacuation order issued by authorities• Avoid areas downwind of the volcanoIf indoors:• Close all windows, doors, and dampers• Put all machinery inside a garage or barn• Bring animals and livestock into closed sheltersIf outdoors:• Seek shelter immediately• If caught in a rockfall, roll into a ball to protect head • Avoid low-lying areas where poisonous gases can collect and floods can be dangerous• If caught near a stream beware of mudflows.• Wear long sleeved shirts and pants• Use goggles to protect eyes and a dust-mask or damp cloth over face to help breathing• Keep car engines turned off• Stay out of the area.• Mudflows can occur when rain falls through ash- carrying clouds or when rivers are dammed during an eruption and are most dangerous close to stream channels; if on a bridge and notice a mudflow upstream, DO NOT cross the bridge - the mudflow can destroy a bridge quickly.

• Listen to radio for emergency information• Stay away from ashfallWhen outside: • Cover mouth and nose to protect from inhaling ash and wear goggles to protect eyes• Keep skin covered to avoid irritation or burns• Avoid contact with any amount of ash if you have a respiratory ailment• Avoid driving in heavy ashfall (it may clog engines and stall vehicles)• Clear roofs of ashfall (could cause buildings to collapse)• Help neighbors who may require special assistance.