The largest volcanic eruption ever recorded is that of the Indonesian island arc volcano Tambora in 1815. This eruption initially killed an estimated 92,000 people, largely from the associated tsunami. The eruption sent so much particulate matter into the atmosphere that it influenced the climate of the planet, cooling the surface and changing patterns of rainfall globally. The year after the eruption is known as "the year without a summer" in reference to the global cooling caused by the eruption, although people at the time did not know the reason for the cooling. In cooler climates, the year without a summer saw snow throughout the summer and crops were not able to grow. In response, great masses of farmers moved from New England in the United States to the Midwest and Central Plains, seeking a better climate for growing crops.
Tambora is located in the Indonesian region, a chain of thousands of islands that stretch from Southeast Asia to Australia. The tectonic origins of these islands are complex and varied, but many of the islands along the southwest part of the chain are volcanic in origin, formed above the Sumatra-Sunda trench system. This trench marks the edge of subduction of the Indian-Australia plate beneath the Philippine-Eurasian plates, which formed a chain of convergent margin island arc volcanoes above the subduction zone. Tambora is one of these volcanoes, located on the island of Sumbawa, east of Java. Tambora is unusual among the volcanoes of the Indonesian chain, as it is located further from the trench (210 miles; 340 km) and further above the subduction zone (110 miles; 175 km) than other volcanoes in the chain. This is related to the fact that Tambora is located at the junction of subducting continental crust from the Australian plate and subducting oceanic crust from the Indian plate. A major fault cutting across the convergent boundary is related to this transition, and the magmas that feed Tambora seem to have risen along fractures along this fault.
Tambora has a history of volcanic eruptions extending back at least 50,000 years. The age difference between successive volcanic layers is large, and there appear to have been as much as 5,000 years between individual large eruptions. This comparatively large time interval may be related to Tam-bora's unusual tectonic setting far from the trench along a fault zone whose origin is related to differences between the types of material being subducted on either side of the fault.
In 1812 Tambora started reawakening with a series of earthquakes plus small steam and ash eruptions. People of the region did not pay much attention to these warnings, having not remembered the ancient eruptions of 5,000 years past. On April 5, 1815, Tambora erupted with an explosion that was heard 800 miles (1,300 km) away in Jakarta. Ash probably reached more than 15 miles (25 km) in the atmosphere but this was only the beginning of what was to be one of history's greatest eruptions. Five days after the initial blast a series of huge explosions rocked the island, sending ash and pumice 25 miles (40 km) into the atmosphere and sending hot pyroclastic flows (nuée ardentes) tumbling down the flanks of the volcano and into the sea, generating tsunamis. When the hot flows entered the cold water, steam eruptions sent additional material into the atmosphere, creating a scene of massive explosive volcanism and wreaking havoc on the surrounding land and marine ecosystems. More than 36 cubic miles (150 km3) were erupted during these explosions from Tambora, more than 100 times the volume of the Mount St. Helens eruption of 1980.
Ash and other volcanic particles such as pumice from the April eruptions of Tambora coved huge areas that stretched many hundreds of miles across Indonesia. Towns located within a few tens of miles experienced strong, hurricane-force winds that carried rock fragments and ash, burying much in their path and causing widespread death and destruction. The ash caused a darkness like night that lasted for days even in locations 40 miles (65 km) from the eruption center, so dense was the ash. Roofs collapsed from the weight of the ash, and 15-foot-(4.5-m-) tall tsunamis were formed when the pyro-clastic flows entered the sea. These tsunamis swept far inland in low-lying areas, killing and sweeping away many people and livestock. A solid layer of ash, lumber, and bodies formed on the sea extending several miles west from the island of sumbawa, and pieces of this floating mass drifted off across the Java sea. Although it is difficult to estimate, at least 92,000 people were killed in this eruption. Crops were incinerated or poisoned and irrigation systems destroyed, resulting in additional famine and disease after the eruption ceased, killing tens of thousands of people that survived the initial eruption, and forcing hundreds of thousands of people to migrate to neighboring islands.
The year of 1816 is known as the year without a summer, caused by the atmospheric cooling from the sulfur dioxide released from Tambora. snow fell in many areas across Europe and in some places was colored yellow and red from the volcanic particles in the atmosphere. Crops failed, people suffered, and social and economic unrest resulted from the poor weather, and the Napoleonic wars soon erupted. Famine swept Europe hitting France especially hard, with food and antitax riots erupting in many places. The number of deaths from the famine in Europe is estimated at another 100,000 people.
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