Lava broad, shallow slopes formed from predominantly effusive eruptions of relatively fluid basaltic lava flows, to steeply-sided stratovolcanoes (also known as composite volcanoes) made of alternating layers of ash and more viscous lava flows typical of intermediate and felsic lavas. A caldera, which is a large subsidence crater, can form in a stratovolcano, if the magma chamber is partially or wholly emptied by large explosive eruptions; the summit cone no longer supports itself and thus collapses in on itself afterwards. Such features may include volcanic crater lakes and lava domes after the event. However, calderas can also form by non-explosive means
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