Sveifluháls is a basaltichyaloclastite ridge, actually a ca. 22 km long tindar complex. It consists as is usual for such subglacially formed volcanoes, of pillow lavas under a layer of phreatomagmatic tephra (hyaloclastite). Pedersen and her coworkers think that the Ice Age glacier which was covering it at time of formation had a thickness between 70 and 400 m.