Lava low degree of polymerization and high temperature favors chemical diffusion, so it is common to see large, well-formed phenocrysts within mafic lavas. Basalt lavas tend to produce low-profile shield volcanoes or "flood basalt fields", because the fluidal lava flows for long distances from the vent. The thickness of a basalt lava, particularly on a low slope, may be much greater than the thickness of the moving lava flow at any one time, because basalt lavas may "inflate" by supply of lava beneath a solidified crust. Most basalt lavas are of "ʻAʻā" or "pāhoehoe" types, rather than block lavas. Underwater, they
Boring Lava Field Boring Lava Field The Boring Lava Field (also known as the Boring Volcanic Field) is an Plio-Pleistocene volcanic field with cinder cones, small shield volcanoes, and lava flows in the northern Willamette Valley of the U. S. state of Oregon. Located southeast of downtown Portland, the field got its name from the town of Boring, Oregon, which lies just to the southeast of the most dense cluster of lava vents. The zone became active about 2.7 million years ago, with long periods of activity interspersed with quiescence. Its last eruptions took place about 57,000 years ago at the Beacon Rock