Tyatya (Russian: Тятя, 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 1,819 metres (5,968 ft). 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.

• List of volcanoes in Russia
• List of ultras of Northeast Asia

• Chachadake (Tiatia): Global Volcanism Program - Smithsonian Institution
• Chachadake - Japan Meteorological Agency (in Japanese)
• "Chachadake: National catalogue of the active volcanoes in Japan" (PDF). - Japan Meteorological Agency
• Chacha Dake (Tyatya) - Geological Survey of Japan