Karymsky is a symmetrical stratovolcano rising within a 5-km-wide caldera that formed during the early Holocene. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been vulcanian or vulcanian-strombolian with moderate explosive activity and occasional lava flows from the summit crater. There is currently an ongoing cycle of non-stop eruption occurring, and is the peninsula's most active, and reliable volcano, which has been erupting continuously since 1996.