The 1815 eruption of Tambora ejected up to 24 cubic miles (100 cubic kilometers) of molten and pulverized rock and spewed 400 million tons of sulfurous gases 27 miles (43 kilometers) into the atmosphere.
By contrast the 1980 eruption of Mount St. Helens in Washington State ejected 0.1 cubic mile (0.5 cubic kilometer) of lava; the 1883 eruption of Krakatau (Krakatoa) in Indonesia ejected 3.5 miles (15 cubic kilometers) of molten rock; Vesuvius ejected 1.4 cubic miles (6 cubic kilometers) of lava.
"[Tambora] is way beyond any of these," Sigurdsson said. "It's truly the largest on Earth in recent history."
Before the eruption the volcano stood at about 13,800 feet (4,200 meters). Today it stands at about 9,200 feet (2,800 meters) and has a 4,100-foot-deep (1,250-meter-deep) caldera, or crater.
The sulfurous gases spewed into the atmosphere by Tambora formed aerosol droplets that reflected the sun's rays before they reached the ground. This caused a year of global cooling in 1816 now known as the year without a summer.
The cooler temperatures triggered widespread crop failures, food shortages, and disease outbreaks, perhaps killing an additional 200,000 people worldwide, Sigurdsson said.
"There were tremendous problems in central Europe and all over the world, including the U.S.," he said.
The growing season in New England shrunk by a hundred days, which historians say prompted many farmers to abandon their fields and head west.
Wanting to know more about this devastating eruption, Sigurdsson traveled to the remote Indonesian island in 1986 with University of Rhode Island colleague Steve Carey to calculate the size of the volcanic blast.
Two years later the pair returned to explore the caldera. A guide told them about pottery fragments and pieces of bronze the local people had found in the jungle 16 miles (25 kilometers) to the west.
"So I went there [in 2004] to start to research in that area and very quickly hit on a site that looked like it was promising," Sigurdsson said.
The newly discovered town is about five miles (eight kilometers) from the coast. Sigurdsson said the inland location was likely for protection from pirates from other islands.
Using ground-penetrating radar, the scientists examined the features beneath the 1815 volcanic deposits. Clues from local people led them to an area named Museum Gully because of the pottery and other artifacts found there.
In six weeks, they excavated the remains of a home, which had been carbonized from the extreme heat of the volcanic eruption.
Most surprising to Sigurdsson were the elegantly decorated pieces of china likely from Cambodia or Vietnam, which suggest the Tamborans were wealthy traders.
"They were pretty well off," he said. "We know these people were traders. They were famous for horse trading."
Historical records also suggest the Tamborans traded in honey, sappanwood used to make red dye, and sandalwood used for incense and medications.
Sigurdsson hopes to return to Sumbawa in late 2006 or 2007 to identify areas for future excavation.
Of keen interest to Sigurdsson is a large wooden "palace" he believes to be near the site, based on observations of similar structures in neighboring towns on the island.
Lape, the University of Washington anthropologist, cautioned that the words "kingdom" and "palace" may conjure up a false image of what really lies beneath the volcanic debris.
Dutch drawings of these places called kingdoms in the East Indies depict "small villages," he said. "So there's a little bit of discord."
Lape added that many of these villages converted to Islam in the mid to late 17th century and took on the hierarchal religious and political structures of Islam.
"But the physical structures don't seem to have been a part of it," he said.
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