Igneous rock the partial melting of rocks within the mantle and crust. Extrusive igneous rocks cool and solidify quicker than intrusive igneous rocks. They are formed by the cooling of molten magma on the earth's surface. The magma, which is brought to the surface through fissures or volcanic eruptions, solidifies at a faster rate. Hence such rocks are smooth, crystalline and fine-grained. Basalt is a common extrusive igneous rock and forms lava flows, lava sheets and lava plateaus. Some kinds of basalt solidify to form long polygonal columns. The Giant's Causeway in Antrim, Northern Ireland is an example. The molten rock, with
Boring Lava Field of the town of Boring. Volcanologists L. Siebert, T. Simkin, and P. Kimberly (2011) of the Global Volcanism Program list its highest elevation as , at Larch Mountain, with most vents reaching an elevation of . Located in the Portland Basin, the field consists of monogenetic volcanic cones that appear as hills throughout the area, reaching heights of above their surroundings. The collection includes more than 80 small volcanic edifices and lava flows in the Portland–Vancouver metropolitan area, with the possibility of more volcanic deposits buried under sedimentary rock layers. The borders for the Boring Lava Field group are clear,