According to the Volcanic Explosivity Index, a VEI of 6 to 8 is classified as ultra-Plinian. Eruptions of this type are defined by ash plumes over high and a volume of erupted material to in size. Eruptions in the ultra-Plinian category include the Lava Creek eruption of the Yellowstone Caldera (c. 640,000 years ago, VEI 8), Lake Toba (c. 74,000 years ago, VEI 8), Tambora (1815, VEI 7), Krakatoa (1883, VEI 6), Akahoya eruption of Kikai Caldera, Japan and the 1991 Mount Pinatubo eruption in the Philippines (VEI 6).