The island has been under Russian administration since the end of World War II, when Soviet forces took possession of the Kurils.

The Lower Complex has been further subdivided into the Rybakov and Kamuy formations (e.g. Zhelubovsky and Pryaluhina;[10] Bevz[11]), although Martynov et al.[12] used a different classification and terminology (see below).

The Rybakov Formation, located in the most uplifted and deeply exhumed blocks, especially in the northern part of the island, was mainly an andesitic volcanic complex.

The Kamuy Formation, which forms the backbone of the island, consisted mainly of flysch-like volcanic-sedimentary deposits rich in felsic pumice of (rhyo)dacitic composition, with a thickness exceeding 1100 m (Martynov et al.[14]).

This suggests that the Fregat volcanic rocks are predominantly of sub-aerial origin, occasionally deposited at shallow depths below sea level.

The northern part of Kunashir showed substantial uplift of over 1 km, in contrast to the more modest elevation change of 200–300 m in the southern region (Syvorotkin and Rusinova, cit opt.).

These volcanoes, characterised by a typical alternation of lava flows and tuff deposits, exhibited mainly basaltic-andesitic to andesitic compositions, with minor amounts of more differentiated magmas of dacitic affinity.

In the Rybakov Formation these intrusions manifested as stocks, dikes and sills of basaltic, andesitic and dacitic composition.

The Valentina Massif, a tonalite-porphyry stock along the Okhotsk coast in the northern part of Kunashir, showed tectonic rather than intrusive contacts.

The climate is humid continental with very heavy precipitation especially in the autumn and a strong seasonal lag with maximum temperatures in August and September.

The vegetation mostly consists of spruce, pine, fir, and mixed deciduous forests with lianas and Kuril bamboo underbrush.

The mountains are covered with birch and Siberian Dwarf Pine scrub, herbaceous flowers or bare rocks.

[23] Vries's account of the area was incredibly garbled[24]—including a fictitious continental extension dubbed Company Land—but while his imaginary Staten Island is usually connected to Iturup,[25] its placement on most maps of the period more closely resembles the location of Kunashir.

[26] The Japanese expanded north to Kunashir in the 18th century, with the Matsumae clan establishing a fishery and trading site called Kunashiri-basho (国後場所) in 1754.

In 1789 Kunashir Island was one of the settings of the Menashi-Kunashiri Battle in which native Ainu revolted against Yamato Japanese tradespeople and colonists.

Russian navigator Vasily Golovnin attempted to map and explore the island in 1811, but was apprehended by Japanese authorities and spent two years in prison.