Mount Tambora. Landsat 7 satellite image in infrared and visible light of Mount Tambora volcano (upper left), Sumbawa Island, Indonesia. Water is blue, vegetation is green, bare land is pink and clouds are white. The volcano's caldera (purple circle), an area of collapsed land resulting from a volcanic eruption, measures 6 kilometres across and is 800 metres deep. The caldera was formed in 1815 after a huge explosion that ejected massive amounts of ash and sulphur dioxide into the atmosphere. Global cooling caused by the eruption led to 1816 being called insthe year without a summerins.