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Icelandic eruption: Apocalypse now? Part 2

 

Icelandic eruption: Apocalypse now? Part 2

The monsters of the world - Historical disaster by volcanoes

Dr. Claus Rink, Geoscientist and Special correspondent
of Pattaya Mail and Chiang Mai Mail

How many active (erupting) volcanoes are known?

20 each year, 50-70 each decade, about 160 historical eruptions, about 550 known Holocene eruptions (last 10,000 years) and about 1300 known before.

Types of volcanoes (USGS)

Typical phenomena happen at a volcano eruption (USGS)


Global Cooling by volcanoes

Global cooling often has been linked with major volcanic eruptions. The year 1816 often has been referred to as “the year without a summer”. It was a time of significant weather-related disruptions in New England and in Western Europe with killing summer frosts in the United States and Canada.

These strange phenomena were attributed to a major eruption of the Tambora volcano in 1815 in Indonesia. The volcano threw sulfur dioxide gas into the stratosphere, and the aerosol layer that formed led to brilliant sunsets seen around the world for several years.

Tambora is on Sumbawa Island along the east Sunda Arc. It lies some 300 kilometers behind the Sunda Trench, but the subduction zone in that area has a shallow dip and is less than 200 kilometers deep beneath Tambora; it is a large stratovolcano. Before its eruption in 1815, Tambora might have been in repose for as much as 5,000 years.


Tambora

At least 6 months and probably about 3 years of increased steaming and small phreatic eruptions preceded the 1815 Tambora eruption, the largest in historical time. A moderately large explosive eruption occurred on 5 April 1815, from which ash fell in east Java and thunder like sounds were heard up to 1,400 kilometers away.

A still larger eruption occurred on 10-11 April, ultimately ejecting about 50 cubic kilometers of magma. The eruption left a deep summit caldera where previously a much higher stratovolcano had stood. Earthquakes were felt as far away as Surabaya (500 kilometers), possibly reflecting the caldera collapse.


Year without summer

Among the more prominent theories of events that have triggered global climatic changes is that we have increases in volcanism that could have thrown more airborne volcanic material into the stratosphere, thereby creating a dust veil and lowered temperatures.

The years 1980, 1981, and 1982, for example, saw several major volcanic eruptions adding large quantities of particulate volcanic material and volatiles to the stratosphere, including the catastrophic eruption of Mount St. Helens, Washington, on May 18, 1980, and a large eruption of Mount Hekla, Iceland, on August 17, 1980.

The 1982 series of eruptions from El Chichon volcano, Mexico, caused death and destruction in the populated area around the volcano, but a further reaching impact may result from the effect on Earth’s climate because of the enormous ejection of volcanic material into the stratosphere.

The potential climatic effect of the Laki volcanic eruption in Iceland in 1783, the largest effusive (lava) volcanic eruption in historic time, was huge.

The catastrophic eruption of the Tambora volcano, Indonesia, in 1815 was followed by a so-called “year-without-a-summer.” In New England, for example, frost occurred during each of the summer months in 1816.


Mount Pinatubo

Mount Pinatubo is one of a chain of composite volcanoes that constitute the Luzon volcanic arc. Before the eruption, more than 30,000 people lived in small villages on the volcano’s flanks.

Mount Pinatubo

The June 1991 eruption of Mount Pinatubo was global. Slightly cooler than usual temperatures recorded worldwide have been attributed to this eruption that sent fine ash and gases high into the stratosphere for 10 weeks, forming a large volcanic cloud that drifted around the world. The sulfur dioxide (SO2) in this cloud - about 22 million tons - combined with water to form droplets of sulfuric acid, blocking some of the sunlight from reaching the Earth and thereby cooling temperatures in some regions by as much as 1.5 degrees C.

An eruption the size of Mount Pinatubo could affect the weather for a few years. A similar phenomenon occurred in April of 1815 with the cataclysmic eruption of Tambora Volcano in Indonesia, the most powerful eruption in recorded history. Tambora’s volcanic cloud lowered global temperatures by as much as 3 degrees C. Even a year after the eruption, most of the northern hemisphere experienced sharply cooler temperatures during the summer months, causing the “year without a summer” in parts of Europe and in North America, as mentioned above.


74,000 years ago: Toba

One eruption happened long ago and far away - about 74,000 years ago on the island of Sumatra. The eruption of the Toba Volcano was the largest eruption in the last two million years, and, according to some theories, almost wiped out our human ancestors.

The scale of the Toba eruption is difficult to comprehend. Pyroclastic flows (hot flows of ash and pumice) covered an area of at least 20,000 square kilometers (7,700 sq mi), with deposits as thick as 600 m (2,000 ft) near the vents.

Ash fall was widespread over much of southeast Asia. An ash layer approximately 15 cm (6 in) thick was deposited over the entire Indian subcontinent. Our appreciation of the magnitude of this eruption continues to grow as Toba ash is recognized farther and farther from the source.

The volume of the Toba eruption is estimated at 2,800 cubic kilometers (670 cu mi). To give some comparison with more recent eruptions, the 1980 eruption of Mount St. Helens produced less than 1 cubic kilometer (0.25 cu mi). Vesuvius (A.D. 79) erupted about 5 cubic kilometers (1.2 cu mi), and Krakatoa in Indonesia (1883) about 12 cubic kilometers (3 cu mi). Closer to home, the volume of Kilauea’s ongoing eruption is about 2.6 cubic kilometers (0.6 cu mi), erupted over the last 22 years.

The most widespread hazard from such an eruption is its effect on global climate. Large, explosive eruptions eject huge amounts of volcanic ash and gas that reach the stratosphere. Sulfur dioxide gas reacts with atmospheric moisture to form tiny droplets of sulfuric acid. The droplets and ash particles both absorb heat and reflect solar radiation, cooling the lower atmosphere. While ash tends to settle out of the stratosphere within months, the aerosol of sulfuric acid can remain in the stratosphere for 2-3 years before dissipating.

Climate catastrophes, which have occurred many times in the geological past, caused the extinction of large or small populations of animals and plants. Changes in the terrestrial and marine biota caused by the catastrophic climate changes undoubtedly resulted in considerable fluctuations in the global carbon cycle and atmospheric gas composition. Primarily, carbon dioxide and other greenhouse gas contents were affected. The study of these catastrophes allows a conclusion that climate system is very sensitive to relatively small changes in climate-forcing factors (transparency of the atmosphere, changes in large glaciations, etc.).

To be continued…