Lake Toba in Sumatra, Indonesia, fills a gigantic caldera 30km wide and 100km long. This caldera has been the site of multiple large explosive eruptions, the largest of which generated the Young Toba Tuff about 75,000 years ago. That pyroclastic deposit covered an area of at least 200,000 square km with a volume of 2800 cubic km, the largest explosive eruption in the last 2,000,000 years.
      Photo copyright A.M. & K.D. Hollitzer (e-mail: holli@tig.com.au)

For additional data see Volcano World