Boring Lava Field | |
|---|---|
 Mount Sylvania in Portland, Oregon, one of the major volcanoes in the field | |
 | |
| Location | Oregon and Washington, U.S. |
| Age | Plio-Pleistocene[1] |
| Highest elevation | 4,061 feet (1,238 m) |
| Last eruption | 57,000 years ago[3][4] |
The Boring Lava Field (also known as the Boring Volcanic Field)[3] is a Plio-Pleistocene volcanic field of cinder cones, small shield volcanoes, and lava flows in the northern Willamette Valley of the U.S. state of Oregon and adjacent southwest Washington. The volcanic field is named for the town of Boring, Oregon, located 12 miles (20 km) southeast of downtown Portland and on the edge of the densest cluster of volcanic vents. The zone became volcanically active about 2.7 million years ago, with long periods of eruptive activity interspersed with quiescence. Its last eruptions took place about 57,000 years ago at the Beacon Rock cinder cone volcano. The individual volcanic vents of the field are considered extinct, but the field itself is not.
The Boring Lava Field covers an area of about 1,500 square miles (3,900 km2) and has a total volume of 2.4 cubic miles (10 km3). This region sustains diverse flora and fauna within its habitat areas, which are subject to Portland's moderate climate. The highest point of the field is at Larch Mountain, which reaches an elevation of 4,055 feet (1,236 m).
The Portland metropolitan area, including suburbs, is one of the few places in the continental United States to have extinct volcanoes within a city's limits. The Boring Lava Field has played an important role in local affairs, including the development of the Robertson Tunnel, recreation, and nature parks. Because of the field's proximity to densely populated areas, eruptive activity would be a threat to human life and property, but the probability for future eruptions affecting the region is very low. The field may also influence future earthquakes in the area, as intrusive rock from its historic eruptions may affect ground movement.
- ^ a b Wood & Kienle 1990, pp. 170–172.
- ^ "Larch Reset". NGS Data Sheet. National Geodetic Survey, National Oceanic and Atmospheric Administration, United States Department of Commerce. Retrieved November 18, 2008.
- ^ a b Cite error: The named reference
cvobvfwas invoked but never defined (see the help page). - ^ Evarts et al. 2009, p. 258.