Geography and geology
Baekdu Mountain is a stratovolcano whose cone is truncated by a large caldera, about 5 km (3.1 mi) wide and 850 m (2,789 ft) deep, partially filled by the waters of Heaven Lake. The caldera was created by a major eruption in 969 AD (± 20 years). Volcanic ash from this eruption has been found as far away as the southern part of Hokkaidō, the northern island of Japan. The lake has a circumference of 12 to 14 kilometres (7.5-8.7 miles), with an average depth of 213 m (699 ft) and maximum depth of 384 m (1,260 ft). From mid-October to mid-June, the lake is typically covered with ice. In 2011, experts in North and South Korea met to discuss the potential for a significant eruption in the near future. as the volcano explodes to life every 100 years or so, the last time in 1903. The central section of the mountain rises about 3 mm every year, due to rising levels of magma below the central part of the mountain. Sixteen peaks exceeding 2,500 m (8,200 ft) line the caldera rim surrounding Heaven Lake. The highest peak, called Janggun Peak, is covered in snow about eight months of the year. The slope is relatively gentle until about 1,800 metres (5,905 ft). Water flows north out of the lake, and near the outlet there is a 70 metre (230 ft) waterfall. The mountain is the source of the Songhua, Tumen and Yalu rivers.
The weather on the mountain can be very erratic, sometimes severe. The annual average temperature at the peak is −8.3 °C (17.1 °F). During summer, temperatures of about 18 °C (64 °F) or higher can be reached, and during winter temperatures can drop to −48 °C (−54 °F). Average temperature is about −24 °C (−11 °F) in January, and 10 °C (50 °F) in July, remaining below freezing for eight months of the year. Average wind speed is 42 kilometres (26.1 mi) per hour, peaking at 63 kilometres (39.1 mi) per hour. Relative humidity averages 74%. Summer snow cover on the peak has reduced dramatically during that time.