A Weblog monitoring coverage of environmental issues and science in the UK media. By Professor Emeritus Philip Stott. The aim is to assess whether a subject is being fairly covered by press, radio, and television. Above all, the Weblog will focus on science, but not just on poor science. It will also bring to public notice good science that is being ignored because it may be politically inconvenient.

Wednesday, January 05, 2005

The biggest volcanic eruption in recorded history.....

To underline the geological power of the mighty subduction zone on which Indonesia rests, I thought it would be useful to recall the fact that the biggest volcanic eruption in recorded history was also an Indonesian event, namely the 1815 eruption of Tambora. Here are some scientific accounts of this truly cataclysmic occurrence:-

I. The Eruption of Tambora 1815

(a) Adapted from: the Smithsonian Institution Global Volcanism Website, 2002:

"The massive Tambora stratovolcano forms the entire 60-kilometer-wide Sanggar Peninsula on northern Sumbawa Island [Indonesia]. Tambora grew to about 4000 metres elevation before forming a caldera more than 43,000 years ago. Late-Pleistocene lava flows largely filled the early caldera, after which activity changed to dominantly explosive eruptions during the early Holocene. Tambora was the source of history's largest explosive eruption, in April 1815. Pyroclastic flows reached the sea on all sides of the peninsula and heavy tephra fall devastated croplands, causing an estimated 60,000 fatalities [the same as the 1755 Lisbon earthquake death toll in Portugal - see below]. The eruption of more than 150 cubic kilometers of tephra formed a 6-kilometer-wide, 1250-metre-deep caldera and produced global climatic effects. Minor lava domes and flows have been extruded on the caldera floor during the 19th and 20th centuries."

(b) Adapted from: Newhall & Dzurisin 1988. 'Historical Unrest at Large Calderas of the World.' (U. S. Geological Survey Bulletin No. 1855):

"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. Tambora is a large stratovolcano composed dominantly of nepheline-normative, leucite-bearing trachybasalt and trachyandesite. Before its eruption in 1815, Tambora might have been in repose for as much as 5,000 years.

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, beginning as three columns of fire rising to a great height, and ultimately ejecting about 50 cubic kilometers of magma (dense rock equivalent). 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.

A small, postcaldera cone and lava flow, Doro Afi Toi, originated sometime between 1847 and 1913. A strong earthquake on 13 January 1909, with an epicentre near Tambora (8.5 degrees S, 117.4 degrees E), was presumably connected with Tambora. Might the earthquake have occurred during formation of Doro Afi Toi?"

II. 'The Year Without a Summer' 1816

(c) Adapted from: NASA's Earth Observing Project Science Webpage: Volcanoes and Global Climate Change, May 2000:

"Global cooling has often been linked with major volcanic eruptions. The year 1816 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 sulphur dioxide gas into the stratosphere, and the aerosol layer that formed led to brilliant sunsets seen around the world for several years." [It is said that artists' palettes were changed by this event.]

(d) Adapted from: Kious & Tilling 1996. This Dynamic Earth: the Story of Plate Tectonics (USGS General Interest Publication):

"The June 1991 eruption of Mount Pinatubo was global. Slightly cooler than usual temperatures recorded worldwide and the brilliant sunsets and sunrises have been attributed to this eruption that sent fine ash and gases high into the stratosphere, forming a large volcanic cloud that drifted around the world. The sulphur dioxide (SO2) in this cloud -- about 22 million tons -- combined with water to form droplets of sulphuric acid, blocking some of the sunlight from reaching the Earth and thereby cooling temperatures in some regions by as much as 0.5°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 the Tambora Volcano in Indonesia, the most powerful eruption in recorded history. Tambora's volcanic cloud lowered global temperatures by as much as 3°C. Even a year after the eruption, most of the northern hemisphere experienced sharply cooler temperatures during the summer months. In parts of Europe and in North America, 1816 was known as 'the year without a summer."

For more on Indonesia's restless world, visit: USGS 'Indonesian Volcanoes and Volcanics', 2004.


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