Simushir is highly elongated, consisting of a series of stratovolcanos. The island has a length of with a width of, and an area of. At the north end of the island is a half-submerged caldera, Brouton Bay, with an entrance only 2.5 meters deep, plunging to 240 meters in the center.
Urataman, high and overlooking Brouton Bay, is the northernmost stratovolcano of the island. Further south are:
Prevo, with a height of. The peak erupted in the early 19th century, forming a symmetrical cone with a resemblance to Mount Fuji. On the summit is a 450 × 600 meter wide summit crater with a small caldera lake on its floor. Lava flows from the summit reach both coasts of central Simushir. Only two eruptions are known from Prevo Peak in historical times. The largest of these, during the 1760s, produced pyroclastic flows that destroyed all vegetation at the foot of the volcano. Weak explosive activity occurred during the most recent eruption, in the early 19th century.
Zavaritzki, with a height of, and a 2 × 3 kilometer fresh water caldera lake.. Several young cones and lava domes are located near the margins the lake. A lava dome created in the 1916 and 1931 eruptions formed a small island in the northern part of the lake. In 1957, a new 350 meter wide, 40 meter high lava dome was created following explosive eruptions, decreasing the size of the lake.
Milna, with a height of, is the highest point on the island. This volcano erupted in 1881 and in 1914. The outer flanks of the steep-sided mountain are dissected by deep gullies, with lava flows extending to the sea. The three kilometer wide caldera was breached to the south due to glaciations.
Goriaschaia Sopka, with a height of, is on the southwest end of the island. This volcano erupted in 1881 and in 1914.
Climate
In spite of its temperate latitude, the powerful Oyashio Current on the western flank of the Aleutian Low gives Simushir a chilly and very wet subarctic climate that amazingly almost qualifies as a polar climate, which in low-lying areas would be expected only at latitudes about 20 degrees or further north. Unlike typical subarctic or polar climates, however, the winters are only moderately severe and there is no permafrost since the mean annual temperature is around, whilst temperatures have never fallen below. However, the extreme winds, which in winter average as much as, make it feel much colder. Summers are mild, but extraordinarily cloudy with fogs occurring on six-sevenths of all days in summer and annual sunshine hours less than 1,100 per year, which is comparable to Reykjavík or the extremely foggy Sichuan Basin. Sunshine is actually most likely in the wettest months of September and October when the heavy rain removes the low-level fog, but clear days are extremely rare at any time of year.
