Mt. Usu located on the southern outer rim of the caldera containing Lake Toya is an active stratovolcano in the Shikotsu-Toya National Park, Hokkaido. At the eruption about 7,000 years ago, the southern flank of the volcano collapsed and produced a debris avalanche that reached the sea, which is now called Funka (Eruption) Bay. The intricate coastline around the bay was formed by this eruption.

Mt. Usu has erupted four times since 1900. Lava domes were formed in the summit caldera about 1.8 km in diameter. Three of these domes, O-Usu, Ko-Usu and Usu-Shinzan, were erupted during this time. Other lava domes including Showa-Shinzan, Mt. Konpira and Meiji-Shinazan were also formed in the montane areas.

The most recent eruption in 2000 is still fresh in our memory and white volcanic smoke is still rising from its summit. The mountain opening ceremony is held on April 29 every year. There is also a ropeway up to the top of the mountain, where two observation decks are located and you can command a magnificent panoramic view of the crater basin, Lake Toya and Funka Bay.