Etorofu-Yakeyama (also known as the Grozny Group), in the center of Iturup Island, contains the complex volcanoes of Etorofu-Yakeyama (Ivan Grozny) and Odamoisan (Tebenkov). The former has a 3-3.5 km diameter caldera that is open to the south, where the large, 1158-m-high andesitic extrusion dome was emplaced.  Several other lava domes of Holocene age were constructed  to the NE; extrusion of these domes has constricted a former lake in the northern side of the caldera to an extremely sinuous shoreline. The forested andesitic Odamoisan lies immediately NE of the Grozny dome complex. The large Machekh crater, which displays strong fumarolic activity, lies immediately south of Odamoisan.  Historical eruptions, the first of which took place in 1968, have been restricted to Etorofu-Yakeyama.