Located in the cold waters of the northwestern Pacific Ocean, the Kuril Islands stretch for 1,250 km from the southern tip of Russia's Kamchatka Peninsula southwards to the Japanese island of Hokkaido, thus forming a neat boundary between the Sea of Okhotsk (on the west) and the Pacific Ocean (on the east). All of the islands fall under Russian jurisdiction, although some of the southern islands are the subject of a long-running territorial dispute with Japan. The chain consists of 22 main islands (most of which are volcanically active) and around 30 smaller islets with a total area of 15,600 km².
The islands are divided into three sub-groups that are separated by deep (up to 2,000 m) straits: the Northern Kuril Islands (Shumshu to Shiashkotan) are separated from the Central Kuril Islands (Matua to Simushir) by the Krusentern Strait. The Central Kuril Islands are, in turn, separated from the Southern Kuril Islands (Chirpoy to Kunashir) by the Boussole Strait.
Several of the islands are large: Iturup (3,200 km²), Paramushir (2,053 km²), Kunashir (1,490 km²) and Urup (1,450 km²) — they are highly distinctive in their narrow and elongate forms that are dotted with chains of volcanoes. Most of the islands are mountainous, although terrain can be highly variable and includes low hills, plains and valleys. Many of the islands are endowed with impressive geological features such as the Tao-Rusyr caldera on Onekotan or the symmetrical cones of volcanoes such Prevo Peak on Simushir. Vulkan Alaid on the island of Atlasova claims the highest elevation of 2,339 m. There are at least 160 volcanoes amongst the islands, 40 of which can be described as currently active — the islands form part of the so-called "Pacific Ring of Fire".
The Kuril Islands are the emergent parts of a geological formation known as the Greater Kuril Ridge, which also includes the Shiretoko Peninsula of Hokkaido. The ridge parallels the Lesser Kuril Ridge in the south — the Lesser Kuril Ridge includes the Nemuro Peninsula of eastern Hokkaido, the Habomai Island group, and continues to the northeast as the submarine Vityaz Ridge. The formation of the islands has taken place through a complicated series of events over the last 90 million years.
Most of the islands are densely vegetated where the terrain allows — in higher areas the vegetation is tundra-like or absent. Flora comprises broadleaf forest, dark coniferous forests, open woodland, grassland and the alpine tundra zone. Vegetation becomes more luxuriant and taller from north to south as the climate becomes milder, eventually allowing the growth of dense stands of Kuril Bamboo on Urup. On all of the islands vegetation type is strongly affected by the vertical relief as well as the islands geographical position within the Kuril chain. Typical Kuril flora includes species such as Alder, Siberian pine, Spruce, and broad leaf forests of Yew, Mulberry, Japanese Stone pine, and Oak.
The islands generally experience a maritime climate with a pronounced variation from north to south. Climate is influenced by the Pacific on the east, the Sea of Okhotsk on the west and by air masses moving in from eastern Asia or the Bering Sea region. The islands are, more often than not, overcast or fog-bound, and thus are quite humid. Precipitation falls throughout the year: 700 to 1,000 mm on the northern islands and 1,000 to 1,100 mm on the southern islands. During the winter this can take the form of extremely heavy snowfalls (many of the images of the islands on this site feature snow-covered islands). During the winter months the Sea of Okhotsk may become extensively choked by ice floes and ice sheets that can block the western coasts of the southern islands.