The Eruption of Krakatoa (1883)

Linor Gruber

Background

Indonesia has the largest amount of volcanoes in the world when compared to other countries. This is due to its unique location in one of the most volatile areas in the world. Indonesia lies within the Pacific Ring of Fire, and more specifically also close to the Alphide Belt, the second largest most active volcanic region in the world (Isreal, 2010). This region was caused by the crash of two tectonic plates, the Eurasian plate and the Indo-Australian plate, and thus caused a giant subduction zone (Volcanoes in Indonesia, 2009).

Krakatoa Island (Krakatau in Indonesian) is a part of Indonesia and lies close to the Java Sea. It is located in between the Islands of Java and Sumatra. Before the eruption, the volcano stood 790 m above sea level. From 1927 till today, in its place now lies the Child of Krakatoa Island as a new volcano has emerged since the eruption of 1883. This new volcano has grown 150 meters in 25 years and is still active today (Maxwell, 2003).

Map
Figure 1. Geographical Location of Krakatoa Island (Chris, 2006).

The Event

Krakatoa was dormant until the period between May and August of 1883. On August 26, 1883, Krakatoa began to erupt and release significant ash clouds a far distance above the island. It was the morning of August 27, 1883 that one of the world’s most astronomical eruptions occurred from the Krakatoa volcano. Initially, there were two small eruptions followed by a larger eruption which cracked the volcano open. This eruption was caused by high pressure buildup in the two underlying tectonic plates. The resulting crack allowed for water to enter the volcano and mix into the magma cavity. This along with the extremely heated steam resulted in extremely intense pressure and an almost complete destruction of the island. This final eruption is one of the biggest the world has ever seen. (Bureau of Meteorology, 2017).

Erupt1
Figure 2. A Depiction of the 1883 Eruption of Krakatoa (Coward and Parker, 1888).

The After Effects

Volume of the Material

The final mega eruption that occurred at Krakatoa was considered to be colossal. On the Volcanic Exclusivity Index it was rated as a number 6, with 7 being the highest rating. Eruptions of this magnitude, are expected to occur only once every couple hundred years on earth(Carayannis, 2001). The eruption caused an enormous plume to rise 40 km high into the air and spread enough material to cover a magnitude of 20 cubic kilometers in the air. To appreciate the enormous size of the eruption, it was recorded that on August 28th, a day after the eruption, the haze caused by the particles in the air had reached South Africa, as atmospheric currents carried the fine particles westward (Scientific American, 2002). By September 9th, it was recorded that the particles had circled the globe, and would continue to circulate it several more times after. (Simkin and Fiske, 1984)

volcano index
Figure 3. The Volcanic Exclusivity Index courtesy of the U.S. Geological Surve (USGS, 2005).

Effects in the Immediate Vicinity

Many devastating effects occurred in the area surrounding the explosion. The islands surrounding Krakatoa (From Sunda Strait to Sumatra) got to witness rain of volcanic ash as well as pumice (a very light and porous volcanic rock formed when a gas-rich froth of glassy lava solidifies rapidly) (Geology, 2005). Everything was covered in a thick layer of ash, killing vegetation, animals and destroying infrastructure. The ash was also hot enough to burn down villages (Edwards, 1895). It is estimated that 10% of the related deaths to the event were caused by burns from the hot volcanic ash (Edwards, 1895). It was only 5 years after the eruption that life on the nearby islands was able to re-establish and rejuvenate itself from devastation (Edwards, 1895).

In addition, the blast waves caused by the eruption were extremely powerful. They were able to break windows and crack walls up to 160km away (Carayannis, 2001).

Furthermore, the giant dust cloud that formed and spread caused darkness in areas more than a 400km radius around the blast. In the immediate area, darkness lasted for more than three days after the eruption. Around the Sunda Straits, darkness lasted from the time of eruption till the 28th of August! (Carayannis, 2001).

Additionally, pumice that formed from the eruption was so large (3 meters thick) that it interfered with water navigation around the surrounding Indonesian islands. Large chunks that formed from the explosion fell into the sea and floated into the ocean. This prohibited some ships from taking their usual route and reach their desired destination. As an interesting fact, some of these large pumice rocks were found afloat two years after the eruption near Melanesia (Carayannis, 2001).

Last, the destruction and sinking of the erupting island caused waves of close to 40 meters to form! These destroyed everything in their path including many of the surrounding islands, 165 coastal villages and hurled ashore 600 tons of coral blocks (Simkin and Fiske, 1984).

pumice1
Figure 4. Pumice (Pumise, 2004).

Effects around the World

The volcanic ash and debris was also able to affect regions and ships around the world. Madagascar, Singapore and Cocos Island got to experience rain of volcanic ash and debris. These regions are more than 1000 km from the site of eruption! Ships up to 6000 km away also experienced similar ash rainfall on deck. In addition, due to this the sun appeared to be blue and green for days after the explosion (Symons, 2007). Vivid red sunsets started appearing worldwide three months after the as the ash and particles continued to spread higher into the atmosphere (Symons, 2007). Due to the haze caused by the ash, a large Corona appeared around the sun and the moon, now referred to as the 'Bishops Ring' (Symons, 2007). The eruption also contributed to global cooling. The volcanic dust and ash in the atmosphere worldwide acted like a solar shield, which as a result lowered global temperature by 1.2 degrees Celsius in the year after the eruption. It was only 5 years later in 1888 that global temperatures returned. (Simkin and Fiske, 1984).

scream
Figure 5. The sunset depicted in the painting, "The Scream", is believed to represent the sunsets that occurred worldwide after the eruption (Munch, 1893).

Fun and Interesting Facts from Effects Around the Globe:

1. No one was hurt from the initial explosion, however due to the after-effects, approximately 36,000 people died due to the catastrophic tsunamis (Bureau of Meteorology, 2017).

2. It is considered to be the loudest sound ever recorded in history. It was heard all the way, 4800 km away in Mauritius (Bureau of Meteorology, 2017).

3. Equivalent to 10,000 times more powerful than the atomic bomb at Hiroshima (Simkin and Fiske, 1984).

4. The explosion was heard over 1/13th of the earth's surface (Simkin and Fiske, 1984).

5. Only 1/3 of the island was left after the eruption (Simkin and Fiske, 1984).

6. The sunset depicted in the painting, "The Scream", is believed to represent the sunsets that occurred worldwide after the eruption (Bureau of Meteorology, 2017).

7. The eruption affected every barometer in the world (Simkin and Fiske, 1984).

8. The large tsunami wave reached Aden in Yemen, Africa in just 12 hours. This trip usually takes a cruise ship twelve days to complete (Simkin and Fiske, 1984).

Lessons Learned and the Science behind Eruptions:

Large, explosive volcanic eruptions inject and produce a significant amount of water vapor, carbon dioxide, sulfur dioxide, hydrogen chloride, hydrogen fluoride and ash (pulverized rock and pumice) into the stratosphere. Even larger amounts are produced when eruptions to the magnitude of Krakatoa are in play. Carbon dioxide plays a critical role as a greenhouse gas once released into the atmosphere. It is able to trap the heat radiated of the surface of the earth and provide insulation for the planet. Sadly, the higher the amount of carbon dioxide that is released into the air that surpasses the original amount needed, leads to global warming as the coat of insulation becomes thicker. When it comes to volcanic activity, volcanoes release approximately 110 million tons of CO2 each year. A greater range comes to play when eruptions the size of Krakatoa erupt. However, on average humans produce more than 10,000 times that amount of CO2 each year. Therefore it is safe to say that the eruption of volcanoes is not a great contributor to global warming (Scientific American, 2002).

The greatest affect on climate caused by volcanoes results from the production of atmospheric haze. When a volcano erupts, sulfur- rich gases and ash particles are released. When Krakatoa's eruption occurred, the gas column it produced was large enough send the particles into the troposphere and the stratosphere. As mentioned before, these particles were then able to travel around the globe several times after the eruption as they were carried west ward by atmospheric currents. These small ash particles block the sun's rays and heat from reaching the surface of the earth. Thus, the temperature on earth is decreased by a significant amount until the particles settle out of the atmosphere. A more drastic effect on climate is caused from sulfurous gases combining with water in the atmosphere to form acidic aerosols. The aerosols absorb the radiation and heat emitted by the sun and release it back out into space, thus causing global cooling. These take many years to settle and remove themselves from the atmospheric layer, hence why their effects are long lasting and influenced globally (Scientific American, 2002).

Furthermore, aerosols induce chemical reactions which alter the chlorine and nitrogen chemical species in the air where they are formed. This reaction causes chlorine monoxide to form and is a chemical that harms and destroys Ozone (McGee et al, 1997). Ozone is a key chemical in blocking the ultraviolet light of the sun from the earth. Without this chemical, humans would be exposed to some of the most harmful rays from the sun possible (Hunt, 2017). Therefore, volcano eruptions can cause a risk for increased volumes of dangerous sunrays to enter the earth (McGee et al, 1997).

Last, during the eruption, the hydrogen chloride and hydrogen fluoride released are dissolved into water droplets. These drops fall down to the ground as acid rain and can cause great damage to the area around the eruption. Acid rain is toxic to an ecosystem as it spreads aluminum into soil, and water streams making highly unsafe and destroying it (McGee et al, 1997).

ozone
Figure 6. A depiction of what happends in the air when a volcano erupts courtesy of the U.S. Geological Surve (Turco, 1992).

The Future

The possibilities of a future eruption in similar size to that of Krakatoa is unknown. Anak Krakatoa remains growing and active. Efforts have been made in order to monitor the activity of volcanoes around Indonesia. "Of the 130 active volcanoes in Indonesia, 67 are equipped with monitoring equipment for study and to warn of imminent eruption." (Edwards, 1895). However an eruption at the same magnitude of Krakatoa is very rare. Close monitoring of activity and providing a warning for people in advance is the best method available at the current time.

anak1
Figure 7. Activity present at Anak Krakatoa (Flydlme, 2008).

References

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Chris, O. (2006, August). "Map of the Sunda Strait, Indonesia.". Retrieved March 15, 2017 from https://en.wikipedia.org/wiki/Krakatoa#/media/File:Sunda_strait_map_v3.png

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