The eruption ejected about of tephra and collapsed the mountain into a caldera, which now contains the crater lake Heaven Lake. The eruption began with a strong Plinian column, and ended with voluminous pyroclastic flows. An average of of Plinian ashfall and coignimbrite ashfall covered about of the Sea of Japan and northern Japan. This ash layer has been named the Baegdusan-Tomakomai ash(B-Tm). It probably occurred in winter in late A.D. 946. This was one of the largest and most violent eruptions in the last 5000 years, along with the Hatepe eruption of Lake Taupo (around 180 AD), the 1257 eruption of Mount Samalas near Mount Rinjani, and the 1815 eruption of Mount Tambora.