island. The land forms of the older rocks are due mainly to 

 erosion whereas the land forms of the sands, ashes and overlying 

 lavas of the central zone are the result of earthquakes and rock 

 accumulation. About one-quarter of the whole area of Iceland is 

 sand and stone desert, and one-eighth is covered with lava. The 

 central part of Iceland is built of younger accumulations of vol- 

 canic products. This process is still going on and there are several 

 volcanoes which have been active in historic times. Volcanoes 

 exist even under the glaciers, and in the sea off southwest Iceland. 



Iceland is mainly a tableland with an average elevation of 2,500 

 to 3,000 feet. There are narrow borders of coastal lands and very 

 small plains in the south and west. Very little of the island can 

 be said to be lowlands. The highlands are considerably dissected 

 by many valleys which cut into the tablelands from all sides. Flat- 

 topped, steep-sided land forms characterize most of the area. 

 Mountains rise above the general level as prominent features of 

 the central zone. The slopes of the peaks and tablelands are cov- 

 ered by frost-riven, rocks, loose and angular. A common phe- 

 nomenon seen in the higher areas is the arrangements of stones 

 in ring enclosing mud. Also, stones in the pebbly flat areas may 

 be sorted into rings with larger stones encircling smaller ones. 

 Much of the grassland and the central desert area is covered by 

 the hummocky surface. These features are a result of frost action 

 and the permafrost which exists in some of the higher areas. 



Over the whole of the island the soil is fairly uniform, being 

 derived from the basic igneous rocks. On the highlands and on 

 the desert regions near the glaciers, the soil has little organic 

 matter. Nearer sea level the humus layer is thicker. In general, 

 the soil is of poor quality. 



DRAINAGE 



The many constantly melting glaciers and the high rainfall of 

 Iceland produce great run-off and rivers are numerous. In the 

 rather extensive central desert, water is lacking because the water 

 sinks into the porous and fractured lavas and volcanic deposits. 

 Subsurface drainage from this area appears at the surface as 

 springs along the desert borders. Both the sediment-laden glacial 

 rivers and the clear nonglacial rivers are for the most part un- 

 navigable because of their steep gradient, torrential currents and 

 their shallow depths in the lowlands. In the dry summer, the 

 clear rivers become small but the glacial rivers carry two to three 



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