What is "tyatya"

Tyatya (, also spelled Tiatia and known as Chachadake (爺爺岳) in Japanese) is a volcano located in the northeastern part of Kunashir Island, Kuril Islands, Russia. It is the highest peak on the island with an elevation of . Tyatya is one of the finest examples anywhere in the world of a somma volcano, a stratovolcano whose summit has collapsed to form a caldera which has then been mostly refilled by a new, younger volcanic cone which rises above the caldera rim.