Six hundred miles east of Jakarta, the capital of Indonesia, Mount Tambora stretches nearly 9,000 feet above the Java Sea on the island of Sumbawa. The volcano originally grew to about 12,000 feet elevation before a major explosion destroyed its summit and left a pre-1815 caldera more than 43,000 years ago. On April 10, 1815 evening, the towering peak exploded violently, killing more than 100,000 people, directly and indirectly, as it spewed rock and ash high into the atmosphere. The eruption, lasting more than three months, is the largest in past 10,000 years and, arguably, the most influential on a global scale.
The eruption emptied about 50-150 cubic km of magma and measures 7 on the VEI scale. It produced a giant plinian eruption column, which is estimated to have reached more 40-50 km altitude, ejecting large amounts of ash and aerosols into the stratosphere. With the cataclysmic eruption, the entire shape of the mountain changed. The caldera — the central peak — collapsed into the magma chamber below, decreasing the height of Mount Tambora by more than 5,000 feet as ash and rock shot up from below. Caldera collapse destroyed 30 km3 of the mountain and formed a 6 km wide and 1250 m deep caldera. Floating islands of pumice 3 miles long were observed in April 1815, and even 4 years later, these islands still hindered navigation. As the intense heat escaped through the vent, the explosion was heard some 1,600 miles away in western Indonesia.
Up until the summer of 1816, with ash still in the upper atmosphere, the long-term consequences of the eruption finally began to take shape, causing the “Year Without a Summer” and wreaking havoc on weather patterns. The reason for the climatic changes was increased absorption of sunlight due to a veil of aerosols (consisting mostly of tiny droplets of H2SO3 acid, formed by SO2 release) that were dispersed around both hemispheres by stratospheric currents from the tall eruption column. Global temperatures dropped by as much as 3 deg C in 1816 and recovered during the following years.