try Lake Toba, indonesia. it's 50 miles across...

Calderas
Lake Toba

Toba

About 75,000 years ago, this Indonesian volcano released about 2,800 km3 DRE (dense rock equivalent) of ejecta, the largest known eruption within the Quaternary Period (last 1.8 million years). In the late 1990s, anthropologist Stanley Ambrose proposed that a volcanic winter induced by this eruption reduced the human population to about 2,000 - 20,000 individuals, resulting in a population bottleneck (see Toba catastrophe theory). More recently several geneticists, including Lynn Jorde and Henry Harpending have proposed that the human race was reduced to approximately five to ten thousand people. Whichever figure is right, the fact remains that the human race seemingly came close to extinction about 75,000 years ago.

Eruptions forming even larger calderas are known, especially La Garita Caldera in the San Juan Mountains of Colorado, where the 5,000 km3 Fish Canyon Tuff was blasted out in a major single eruption about 27.8 million years ago.

The Toba eruption (the Toba event) occurred at what is now Lake Toba about 67,500 to 75,500 years ago. It had an estimated Volcanic Explosivity Index of 8 (described as "mega-colossal"), making it possibly the largest explosive volcanic eruption within the last twenty-five million years. Bill Rose and Craig Chesner of Michigan Technological University deduced that the total amount of erupted material was about 2800 cubic km (670 cubic miles) — around 2,000 km³ of ignimbrite that flowed over the ground and around 800 km³ that fell as ash, with the wind blowing most of it to the west. The pyroclastic flows of the eruption destroyed an area of 20,000 square kilometers (7,700 square miles), with ash deposits as thick as 600 meters (2000 feet) by the main vent. By contrast, the 1980 eruption of Mount St. Helens ejected around 1.2 cubic km of material, whilst the largest volcanic eruption in historic times, at Mount Tambora in 1815, emitted the equivalent of around 100 cubic kilometres of dense rock and created the "Year Without a Summer" as far away as North America. The eruption was also about three times the size of the latest Yellowstone eruption of Lava Creek 630,000 years ago