The snow and ice-covered elevated region that stretches across Iceland from the SE. to NO. acts as a watershed and divides the island into two large natural regions. However, many glaciers are also found in marginal regions. Together, Iceland’s glaciers cover an area of approximately 13,000 sq km. (1 / 8 of the island’s surface). The snowline reaches the lowest altitudes (400 m.) In the north-west peninsula, while it reaches the highest altitudes in the south-east, at N. del Vatna jökull (1300 m.) Where the internal elevated region reaches the its maximum width and its maximum height. Here lies the largest glacier in Europe, the Vatna or Klofa jökull (8500 sq km), on whose surface some nunatakker (i.e. spikes or peaks protruding from the ice). One of them, which is surrounded by Öræfa jökull, has a height of 2119 m. and it is the highest point in Iceland. Northwest of Vatna jökull, the inner plateau becomes narrower. Almost in the center of the island the Tungnafells jökull and the Hofs jökull (1725 m.) Are located one next to the other; and between them passes a road that connects the northern part with the southern part of the island. To the west of these two glaciers the internal elevated region widens into an important group of glaciers (about 1375 sq km) of which the main part is constituted by the Lang jökull. The highest glacier of this group, however, is the Eiriks jökull (1798 m.) Which has a domed shape. Northwest of Lang jökull is the Holtavördu heidhi, a plateau of 300-500m. in height, from which the reliefs of the north-western peninsula branch off on one side with the extensive Gláma and Dranga glaciers, and on the other the reliefs of the Snæfellsnes peninsula with the imposing Snæfells jökull (1436 m.). To the south of Lang jökull there are several mountain ranges to the West and S., including those of the Reykjanes peninsula.
From the internal elevated region more or less incised bumps branch off, separating the river valleys; eg from Skaptár jökull branches off towards SW. a plateau whose edge is surrounded by arduous ridges and which ends with a group of glaciers, the third largest in Iceland. To this group belong: Torfa jökull, Tindfjalla jökull and Merkur-, Godalands-, Mýrdals- and Eyjafjallajöklarna, which form a single glacier. The great internal relief appears flatter, but in the northern part, north of Vatna jökull it slopes gently down to the low hills of Langanes and the almost flat coast of the northern peninsula, Melrakkasljetta. The largest lowland on the island, extending from the southern coasts almost to the inland mountainous region, between Ingólfs fjall and Eyjafjalla jökull, it covers an area of 4400 sq km. The recent volcanic formations, which have interposed among the oldest and have covered them, are located in a very large area with a SW direction. between Axar fjördhur and Skjálfandi towards Reykjanes. South of the Axar fjördhur is the Skinnstakkahraun. From the Skjálfandi along the Laxá river to Lake Mývatn where this river originates, the Laxá and the Mývatn hraun stretch out (the latter was formed between 1724-29 thanks to the Krafla and Leirhnúkur volcanoes, now extinct); south of these is the Ódádhahraun, the largest lava desert in Iceland, formed in historical times (1151, 1188, 1360) by the volcanoes Trölla dyngja (1491 m.) and Askja (1412 m.).
East of the Ódádhahraun are the Mývatnsöraefi, the largest Icelandic sand deserts, also formed by the volcanoes just mentioned. Other sandy deserts of somewhat different origin can be found south of Askja, between Öræfa, Skeidharár jökull and the sea. A little to the west of these is the Skaptá crater, formed in 1783; to the south-west of it extends along the coasts and right at the foot of Mýrdals jökull the Mýrdals sandur, and to the west of Skaptá, in the lowland, is the Hekla volcano, the most active and best known in Iceland. The Hekla (the name means cloak, to always be covered with snow), forms a hump (1557 m.) of lava and tuff with several craters. The volcanic materials it erupted occupy an area of about 400 sq km. In historical times it has had 22 major eruptions, the last in 1913. In the eruption of 1294 there were numerous victims; the rivers changed direction, and the erupted pumice, floating on the sea, reached the Faeroes. The great Thingvallahravn lava field goes back to prehistoric times. Much older are the hrauns that occupy most of Ölfusaheidi and the Reykjanes peninsula. Even at the bottom of the sea, not far from Reykjanes, several eruptions took place (1211, 1422, 1783), which formed islands which later disappeared. Numerous hrauns are also found in Snæfellsnesand especially around glaciers. In the lavas there are notable caves, such as the Hallshellir near Thingvellir, the Surtshellir in Eiriks jökull and the Raufarhólshellir discovered in 1909, about 30 km away. from Reykjavík.
Other volcanic manifestations are frequent earthquakes as well as mineral springs, sometimes cold or tepid, sometimes hot; there are numerous geysers, such as the Great Geyser and the Uxahver in the SW. by Skjálfandi. Sulfur springs are found near Krísuvík on the Reykjanes peninsula, in northern Iceland east of Mývatn and in the center of the island in Kerlingar fjöll. In these localities the sulfur was also occasionally used, but the deposits are not so rich as to be able to compete with the Sicilian sulfur.
Iceland is situated on an underwater ridge, which stretches from Scotland to Greenland and is surrounded by an underwater plateau, 15 to 100km wide. and about 200 m deep; there are extensive fishing schools. Due to the proximity of a branch of the Gulf Stream, the sea around Iceland is relatively warm; nevertheless the polar current coming from Greenland carries with it from time to time large masses of ice which remain off the northern coasts of Iceland until late summer.
The eastern coasts are affected by the influence of another polar current coming from the NE. In front of the promontories, these different currents produce, together with the ebb and flow, impetuous eddies that make navigation very difficult, also hampered by floating ice and terrible storms.