by George Weber
Toba Volcano: 1. Introduction
When Toba volcano in western Sumatra erupted 73,000 +/- 4000 years ago it was (and still is) the largest volcanic cataclysm to have taken place on planet earth for the last 28 million years.
The eruption happened at a crucial time in the development of anatomically modern humans. We will explore how, whether and to what extent the Toba eruption and its climatic aftermath has influenced the development and spread of modern Homo sapiens.
Therefore, the last Toba eruption (also called the YTT event for "Younger Toba Tuff", see chapter 3 below) is of enormous scientific and general interest. This article attempts to give an overview and introduction to the subject, based on the ongoing work of many scientists in many fields. It is also hoped that the article will raise interest among both lay people and scientists in the subject.
Fig. 1-1. Toba eruption compared to other major eruptions.
The Volcanic Explosivity Index (VEI) is used to classify eruptions:
|VEI||Plume height||DRE estimated
|0||<100 m||>1000 cu m||Hawaiian||Kilauea, repeated|
|1||100 - 1000 m||>10,000 cu m||Hawaiian / Strombolian||Stromboli, repeated|
|2||1 - 5 km||>1 million cu m||Strombolian /Volcanian||Galeras 1992|
|3||3 - 15 km||>10 million cu m||Volcanian||Ruiz 1985|
|4||10 - 25 km||>100 million cu m||Volcanian / Plinian||Galunggung 1822|
|5||>25 km||>1 cu km||Plinian||Mt. St. Helens 1980|
|6||>25 km||>10 cu km||Plinian / Ultra-Plinian||Krakatoa 1883|
|7||>25 km||>100 cu km||Ultra-Plinian||Tambora 1815|
|8||>25 km||>1000 cu km||Ultra-Plinian||Toba 73,000 years ago|
4. Killed 4,000 local people directly
5. Killed 57 local people directly
6. Earthquakes and streams drying up observed and distant rumblings heard in the Andamans;killed ca. 36,000 people, mostly through tidal wave along the Java coast
7. Killed 12,000 local people directly and more than 80,000 worldwide through starvation (crop failures in the "Year without Summer")
Fig. 1-2b. The location of Toba volcano.
Fig. 1-3. The deep Java trench marks the line where the Indo-Australian plate subducts, i.e. slips under, the section of the Eurasian plate on which Indonesia sits. While sinking, the Indo-Australian plate heats up and its water content turns to superheated steam under enormous pressure.. Prodigious energies are generated and a part of these energies are released by the volcanoes on the fault line. The speed of that push is 70 mm (2.75 in.) per year, adding up to more than 5 km (3.1 miles) in the 73,000 years since the last major Toba eruption.
Plate 1-4. Plates moving above and below each other create volcanoes and earthquakes
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Last changed 1 February 2006