The interaction of subglacial volcanoes and their overlying ice cover is characterised by large-scale floods, jökulhlaups, carrying sediment, fresh volcanogenic material and ice.
Öræfajökull (highest peak 2119 m, 13 peaks higher than 1500 m) is a steep, ice-covered cone which has erupted twice since
Snæfellsjökull, like Öræfajökull and Eyjafjallajökull, is a high ice-capped cone (1446 m) rising up from sea level with a 200 m deep summit crater completely infilled with ice. Three eruptions are known of in the Holocene, the most recent around 1750 radiocarbon years ago produced lava and tephra-fall. Snæfellsjökull is the central focus of a national park, a popular tourist location within sight of Reykjavík. Should a flood occur here in the future, the communities and tourist centres throughout the national park, several farms, airfields, the main road and bridges may all be within the most hazardous regions.