The Kuril Islands began forming 90 million years ago during the Cretaceous Period when an oceanic tectonic plate collided with the Siberian continent. Resulting volcanic activity from this tectonic movement eventually formed an underwater ridge, from which the present-day Kuril Islands emerged. The islands, however, were not formed at the same time. The oldest rocks on Urup Island, in the south, formed 4.21 million years ago while those on Ekarma, in the central islands, formed 0.43 million years ago. Thus the older islands are in the south and become younger towards the north.

The Kuril Islands are still tectonically and volcanically active, with 32 volcanoes that are known to have erupted during the past 300 years, including 20 that have erupted since 1945. The same tectonic activity responsible for volcanic eruptions throughout the Kuril Islands has also caused at least 38 earthquake and tsunami events since 1974. In both November 2006 and January 2007, two offshore earthquakes generated tsunamis that produced waves onshore up to 72 ft (22 m) above sea level.

A variety of igneous rocks, resulting from tectonic processes, and sedimentary rocks, formed by depositional processes, are found in the Kuril Islands. Basalt and chalcedony are common igneous rocks, while chert is the most abundant type of sedimentary rock. This results in a wide distribution of various lithic (stone) raw materials across the island chain that would have been available for stone tool production.