The Long Term Effects of Volcanic Eruptions

Steps undertaken to mitigate effects

Over the months and years following the eruptions, artificial embankments have been built to prevent the flooding of inhabited and cultivated area. Decisive human efforts undertaken before, during and after the 1991 eruption reduced the loss of human life and mitigated the financial losses. Even so, the eruption caused an enormous disturbance in the geological balance of a vast area, a disturbance that will have effect on the inhabitants and the environment for many years to come.

Krakatau

Introduction to Krakatau

Krakatau is a volcanic island located between Java and Sumatra, in the center of the Sunda Strait. Before its infamous 1883 eruption, Krakatau had been composed of a row of three volcanic cones inside an ancient caldera. In the year 1883, one by one the three cones began activity. From May to mid-August, the volcanic activity was not very explosive. The violent eruptions only began late August, reaching their high point on August 27.

Devastating eruption (1883, August 26-27)

Mount Krakatoa erupted on The eruption destroyed more than 2/3 of the island of Krakatau and 165 towns and villages were destroyed. There was also a great loss of life as many also were killed by the tsunamis that followed the eruption. The sound of the explosion could be heard from Australia, more than 4000 km away.

Long-term effects

The volcanic eruption produced seaquakes that caused 100-foot high tsunamis that circled the globe six and a half times and drowned more than 36,000. Sea waves caused by the blast were still recorded a week after the initial eruption. In addition to that, the shockwave produced also circled the planet a total of 3 times. More than a year afterward, floating islands of pumice from Krakatau were discovered 7,500 miles away. Dust particles were carried 50 miles high into the stratosphere, where they were blown all over the world. For a full year after the event, only 87% of sunlight was able to shine through the particles in the atmosphere and reach earth.

The eruption had generated 30-70 metric tons of sulfate aerosols in the stratosphere. This caused the sun to appear to be blue-green. Moreover, the increased amount of sulfuric acid concentration in the atmosphere drastically increased in reflectivity or albedo which in turn caused more incoming rays from the sun to be reflected back into the atmosphere. Clouds play an important role in keeping the Earth cool by reflecting sunlight, but they can also serve as blankets to trap warmth. This, along with the large amount of dust particles in the atmosphere, caused global temperatures to fall by approximately 1.2 degrees Celsius.

The Krakatau eruption in 1883 has also been credited with causing the emergence of noctilucent clouds. Noctilucent clouds are bright clouds, seen at twilight, that are located high above the Earth’s surfaces in the mesosphere which is rare as clouds are generally unable to reach such altitudes given the thin air pressure. These special clouds are only able to be seen when they are illuminated by sunlight from below the horizon. The first instance of noctilucent clouds was reported in 1885, soon after the infamous 1883 eruption, prior to which they did not exist.

Mount St Helens

Introduction to Mount St Helens

The formation of Mount St Helens began in the Pleistocene, and much of its massif, the block of the earth's crust bounded by faults and shifted to form peaks of a mountain range, was produced by basaltic and andesitic lava flows. The summit area, or what remains of it, is 2200 years old. Mount St Helens is probably the most active volcano in the Cascade Range. The Cascade Range is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. Before the major eruption in 1980, St Helens was composed of a regular cone, with a base diameter of about 7km, reaching an overall height of almost 9840 feet, approximately 3000m. A series of minor earthquakes signaled that the volcano would return to activity.

The explosion of the magma accumulated in the mountains. Simultaneously, cloud of gas and debris blasted northward by the explosion and traveled at supersonic speed at an estimated temperature of 250 degree C, devastating almost 232 square miles or 600 km2 of forest land. Vertical column of gas and ash formed over the volcano reaching a height of about 16km. following that, a series of pyroclastic flow descended along the valleys of the volcano. Around 5pm paroxysmal phase of the eruption ended leaving a destroyed landscape and a gutted mountain. Following the eruption, a series of lahars added further damage to the surrounding territory causing devastation in many of the river valleys that spread out from the volcano. After the may 18 eruption, st Helens erupted 5 more times but none as intense as the first. Some small eruptions that occur during winter months melt part of the snow cover setting off lahars and avalanches.

Mauna Loa

Introduction

Being 4km above sea level and another 13 km below sea level, the shield volcano Mauna Loa that stands at 17km above its base is known as the world’s largest volcano. It is situated on the Island of Hawaii and having erupted for 33 times since 1843, it is one of most active shield volcanoes in the world. Its last eruption was in 1984. There are no records of deaths directly caused by Mauna Loa volcanic eruptions. The only way the eruption has made an impact was by destroying property and cities. For instance, in 1881 an enormous lava flow stopped right outside the city of Hilo after traveling a distance of 47km. The city narrowly escaped destruction.

Impact

People living in the vicinity are most likely be impacted by the lava flow of Mauna Loa. Although lava flow is quite slow and people are able to escape from it, the intensity of the eruption can be so great that it causes the lava from the volcano to flow at a much faster rate. This covers the viscosity of the lava. Besides this, the volcano is also steep thus contributing to a higher viscosity. Also, the high volume and long lengths which causes the lava to reach the sea also account for the hazards.

It is the lava flows that pose a threat to people living along the slopes of the volcano and their properties there. Volcanic eruptions in 1926 and 1950 destroyed the villages of Hoʻōpūloa Makai and Hoʻokena Mauka on the island respectively leaving dwellers there homeless. In 1935, Mauna Loa had such a huge eruption that the flow of lava threatened to destroy Hilo, a city which arose due to the lava solidifying as it flowed from the same volcano. This flow of lava created such a large power of air that the United States Air force were forced to drop bombs before the lava flowing could reach Hilo in order to prevent it from destroying the island.

If Mauna Loa erupts, it is probable that it will flow through hotels from Waikoloa to Puaka which will heavily impact the economy of the Island of Hawaii.

How to mitigate these effects?

Authorities have to create awareness to the residents of those living near the volcano on how to react and what to do should there be an eruption in the future. They have to be prepared and be able to accurately calculate approximately the least time there is to respond so that they can evacuate to a safer place in time, and not overestimate the time there is. Also, authorities should set up a volcanic warning plan so that they can successfully counter the unforeseen circumstances should the volcano suddenly erupt.

Furthermore, Mauna Loa, along with the neighboring volcano Kilauea, is one of the most studied volcanoes in the world. Because of this, models of the volcano’s behaviour can be created based on its eruptive history. This can assist scientists in predicting the next eruption and thus giving ample time for villagers living near Mauna Loa to evacuate.

How to deal with certain effects

Pyroclastic flows

Pyroclastic flows travel so rapidly that it is pointless to try and divert its direction once it has started. Besides this, pyroclastic flows are also able to “climb” or flow over obstacles hence creating obstacles would not exactly be effective. According to the book, “Volcanoes”, by David A. Rothery, the only logical way to protect property from a pyroclastic flow is to construct a sequence of barriers of about 30m high designed to channel the flow upwards. This would hopefully allow the flow to form a buoyant plume. Although expensive, this method may help make a pyroclastic flow less a hazard.

Ashfall

After an eruption, the air in areas within the vicinity of the explosion – or sometimes even further -- will be heavy with ash and polluted with harmful gases for quite some time. This can prove to be a health hazard. Since ashfall cannot be prevented, the public has to take precautionary measures. For instance, during that period when the air is still heavily polluted, people living in the vicinity can wear protective clothing and high-efficiency dust masks to prevent inhalation of dust particles. Furthermore, drivers should also keep a fair distance between vehicles because of the reduced visibility.

Which volcano is most likely to cause most long-term damage when it erupts? Why?

                                

                                

From the book Volcanoes by Mauro Rosi, PaoloPapale, Luca Lupi, Marco Stoppato

Analysis of diagram

From the diagram, it can be seen that among the volcanoes Pinatubo, St Helen’s and Krakatau, based on their most significant and recent eruptions, Krakatau emitted the highest volume of material – as much as 20km3. We therefore believe that Krakatau would cause the most long-term damage if it were to erupt again. Since more materials like ash, gas and volcanic debris are discharged, there is a higher possibility that it will disturb the climate and destroy the vegetation to a greater extent as compared to the other two volcanoes. Furthermore, since Krakatau has the longest period of quiescence among the three volcanoes, we also assume that the accumulation of pressure is larger. Thus, we believe that the next time Krakatau erupts, the effects will be more damaging and devastating than the other two.

Comparing the pressure build-ups of the three volcanoes

Mount St. Helens

Studies have shown that although the volcano emits steam frequently, there has been no eruption since 1985. However, since there is still the presence of hot magma underneath the mountain, there is always a possibility of another eruption. Even so, scientists state that the eruptions would be relatively small and a large eruption like the one in 1980 would be highly unlikely.

The reason the 1980 eruption was so massive was because the volcanic cone kept the magma from erupting. This caused a large amount of pressure to build up. Thus when the volcano finally erupted in 1980, the eruption was large. However since the top of the volcano is now gone, there is less weight preventing the magma from erupting. This means that the eruptions will occur after smaller amounts of pressure have built up. Thus, the subsequent eruptions of Mount St Helen’s should not be as damaging or devastating. The air pollution and damage to vegetation should not be as drastic as that in 1980.

Once St Helens recovers to its original cone-shape however, it is highly likely that a large-scale eruption will occur. Nevertheless, this would not happen for at least another few centuries.

Mauna Loa

As compared to the other two volcanoes, Mauna Loa erupts the most frequently, with 33 known eruptions since 1843. The eruptions were fairly small and non-violent—in comparison to Krakatau and St Helens -- and the long-term damage is minimal as mentioned in an earlier section in the report. Thus since the periods in between eruptions are fairly short, we conclude that the pressure-buildup is small. Hence, if Mauna Loa were to erupt again, we believe that the long-term damage would not be as devastating as Krakatau or St Helens as it will most likely be a non-violent eruption. The less violent the eruption, the amount of lava and gases emitted will be smaller.

Krakatau

Krakatau has not erupted since 1883, which means it has the longest period of inactivity among the three volcanoes. Hence, as mentioned earlier, since Krakatau has the longest period of quiescence, we can safely assume that the pressure-buildup is larger. Thus, we believe that the next time Krakatau erupts, the eruption will be a violent one. The more violent the explosion, the higher the probability that it will affect the climate and make radical changes to the environment.

In conclusion, we believe that if Krakatau were to erupt, it would cause the most damaging long-term effects as it is highly probable that its eruption will be a violent one.

Volcano eruptions will also be a concern to people. This is because, there will be a greater risk and impact on the country’s economy as we venture into a more and more developed society where each event will heavily cause knock-on effect on others. [I don’t know where to insert!]

Bibliography

http://en.wikipedia.org/wiki/Krakatoa#After_eruptions

http://library.thinkquest.org/C003603/english/volcanoes/casestudies.shtml#19

http://www.windows.ucar.edu/tour/link=/earth/climate/geosphere_case_study.html

http://en.wikipedia.org/wiki/Albedo#Clouds

http://hvo.wr.usgs.gov/maunaloa/

http://en.wikipedia.org/wiki/Mauna_Loa

http://hvo.wr.usgs.gov/volcanowatch/2002/02_01_17.html

http://www.ingentaconnect.com/content/klu/445/2004/00000066/00000006/art00005

http://www.cambodianonline.net/earthvolcano003.htm

http://volcano.und.edu/vwdocs/frequent_questions/top_101/Helen.html

http://volcanoes.usgs.gov/ash/health/#mitigation

Volcanoes by David A. Rothery, published 2003

Volcanoes by Mauro Rosi, PaoloPapale, Luca Lupi, Marco Stoppato, published 2003

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