like Viðey and Kjarlarnes. Volcanic and glacial sediments outcrop at some places around Reykjavík, especially in Fossvogur. Subglacial volcanoes Iceland was heavily ice covered during the glaciations and even completely ice covered during parts of them. As a result, there are hundreds of subglacially formed volcanoes on Iceland. On Reykjanes Peninsula, glaciers were present until around 15,000 -12,000 years ago. Most subglacial edifices are thought to be Weichselian, with a few being older. The subglacial volcanoes can be identified according to type as tuyas (bigger edifices whose upper parts are covered by the products of subaerial eruptions), hyaloclastite ridges (also called tindars) which means elongated subglacially formed volcanic edifices of different sizes, and cone-like subglacial mounds (very rare). There are many hyaloclastite ridges, with most consisting of mixtures of pillow lavas, hyaloclastite and lapilli tuff. There are also elongated pillow structures, called pillow tindars. Examples on Reykjanes peninsula are Sveifluháls, Núpshlíðarháls , Undirhlíðar , Helgafell and Vífilsfell. The tuyas are often sorted according to their form (morphology) into flat-topped tuyas, elongated tuyas, conical tuyas and complex tuyas. The prominent igneous rock is basalt, though there are also some basaltic andesite or andesite volcanoes on Reykjanes, like Húsmúli and Stapafell within the Hengill Volcanic System. Examples for tuyas on Reykjanes Peninsula are Keilir (conical tuya), Geitafell (Brennisteinsfjöll), Geitahlíð and Þorbjörn are flat-topped tuyas whereas Þorðarfell and Syllingarfell are complex tuyas. Postglacial shield volcanoes The Holocene shield volcanoes represent the great bulk of magma production in this part of Iceland and form the base of many other volcanic landforms. Olivine tholeiites constitute about 60% by volume of all post-glacial lava products on the Reykjanes Peninsula." The postglacial shield volcanoes are situated at the periphery of fissure systems. They erupted after the Weichselian glaciation. These shields are mostly circular in form, built up from pāhoehoe lavas and composed of a low-sloping lava cone surrounded by a lava apron; the older shields are made from picrite, the younger, bigger ones from olivine-tholeiite. They were probably formed in long-lived eruptions (years to decades). The best known edifices are Selvogsheiði (height 176 m, basal width 4.8 km, summit width 0.7 km, volume 0.64 km3), Þráinskjöldur (volume 5.2 km3), Heiðin há (volume 6 km3) and Sandfellshæð (4.5 km3). Sandfellshæð is a very regularly constructed shield volcano and the largest in the southern part of Reykjanes Peninsula. Another important shield volcano on Reykjanes Peninsula is Leitin, formed around