Boring Lava Field
The Boring Lava Field 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 southeast of downtown Portland and on the edge of the densest cluster of volcanic vents. The zone became volcanically active about 2.7million 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 and has a total volume of. 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.
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.
Geography
The Boring Lava deposits received their name based on their proximity to the town of Boring, which lies southeast of downtown Portland. The term "Boring Lava" is often used to refer to the local deposits erupted by vents in the field. They are located in the western portion of Oregon. The deposits were given this name by R. Treasher in 1942. In 2002, as geochemical and geochronological information on the Boring deposits accumulated, they were designated part of the larger Boring Lava Field. This grouping is somewhat informal and is based on similarities in age and lithology.The Boring Lava deposits lie west of the town of Boring. The Global Volcanism Program lists the volcanic field's highest elevation as, at Larch Mountain; most vents reach 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, except on the eastern side, where distinctions between Boring deposits and those from the major Cascade Volcanoes are less clear; many geologists have arbitrarily placed the eastern border at a longitude of 122degrees west. In total, the Boring Lava Field covers an area of about, and it has a total volume of.
Physical geography
With a variable topography, the Portland area ranges from river valley floors to terraces reaching elevations of. The Willamette Valley is marked by hills reaching heights of more than, and it is also physically separated from the lower Columbia River valley. The Columbia River flows west from the eastern Portland region, merging with the Willamette near Portland before moving north. Tributaries for the Willamette include the Pudding, Molalla, Tualatin, Abernethy, and Clackamas rivers; tributaries for the Columbia River include the Washougal and Sandy rivers. The Columbia River has significantly shaped the geology of the area.Multnomah Creek drains from Larch Mountain, one of the volcanic cones in Boring Lava Field. Local streams near the community of Boring receive seepage from the local aquifer. This aquifer, part of the greater Troutdale sandstone aquifer, is made of sandstone and conglomerate and supplies water to domestic wells in the Mount Norway area. Boring Lava is known to have formed intrusions into local sedimentary rock, and thus it may guide flow of groundwater locally.
Climate
Portland's climate is moderate, with long growing seasons, moderate rainfail, mild winters, and warm, dry summer seasons. The area has more than 200 frost-free days annually. Temperature can vary widely, reaching a historic maximum of, though the usual July maximum is below, and the average minimum for January is above. Yearly, precipitation averages between in most river valleys, with a mean of from 1871 through 1952. It shows variability, with a historic low of at Portland in 1929 and a maximum of in 1882. More than 75 percent of this precipitation occurs between October and March; July and August mark the driest months with means below, while November, December, and January represent the wettest with averages greater than. Prevailing winds originate from the south during winter and from the northwest during the summer season, with the exception of prevailing winds at the mouth of the Columbia River Gorge, where winds predominantly move to the east. The southern winds have the highest velocities of the three, only rarely occurring with potentially destructive force.Ecology
The Portland area has a moderate climate, and precipitation is not typically very heavy, allowing for significant growth of vegetation, which can hamper fieldwork in the area. Many forests that covered the area were partly cleared for agriculture, timber, or cemetery applications in the early 20th century. These cleared and burned land plots sustain rich stands of secondary forest, featuring gorse, huckleberry, nettles, poison oak, salal, and blackberry. Myriad species of fern, as well as rapid-growth deciduous trees like alder and vine maple are also frequent. Forests support stands of Douglas fir, western hemlock, western redcedar, Pacific dogwood, bigleaf maple, Oregon ash, red alder, cascara buckthorn, Pacific madrone, and Oregon white oak; within swamps and moist areas in creeks, the shrub Devil's club can be observed. Other trees that sometimes dominate forest areas include black cottonwood and red alder. Forest communities have many additional shrubs including Indian plum, western hazel, and snowberry. Ground layer plants include the herbaceous sword fern and stinging nettle.In contemporary times, clearing of forests for housing development has left about half of the Boring Lava region un-forested. As a result, water quality has decreased due to higher sedimentation and turbidity, and flooding has worsened over time. Streams within the area are of either first or second order, with moderate to low flows and average gradients between 10 and 12percent. Cool and clear, many sustain macroinvertebrates, and a smaller number support amphibians and fish. The riparian zones in the Lava Field area host diverse species, and they are influenced by uplands that serve as migration connections for birds, mammals, reptiles, and some amphibians.
The United States Fish and Wildlife Service provided a list of potentially threatened or endangered species in the Boring Lava area, labeling them "sensitive" species. Among plant species, they determined the following species to be sensitive: whitetop aster, golden Indian paintbrush, tall bugbane, pale larkspur, peacock larkspur, Willamette daisy, water howellia, Bradshaw's lomatium, Kincaid's lupine, Howell's montia, Nelson's checkermallow, and Oregon sullivantia. For animal and marine life, northwestern pond turtles, willow flycatchers, long-eared myotises, fringed myotises, long-legged myotises, Yuma myotises, Pacific western big-eared bats, and northern red-legged frogs have been identified as species of concern; pileated woodpeckers, bald eagles, cutthroat trout, and coho salmon are also considered sensitive.
History
The nearby Portland area was inhabited by the Chinook people, though much of the local indigenous culture is poorly understood as a result of disturbance of archeological sites and artifacts by erosion and human development. Oral history, limited archeological evidence, and ethnographic research inform current knowledge about local Native American communities. The area surrounding Portland constituted one of the most densely populated communities in the Pacific Northwest, made up predominantly of Chinook people including the Multnomah and the Clackamas. In 1805 and 1806, Meriwether Lewis and William Clark documented villages and encampments near what is now East Portland, trading with members of the community and describing their plank houses, language, customs, and material culture. Chinookian villages married amongst themselves and with members of the Tualatin tribe as well as the coastal Tillamook people. They imported slaves, traded among villages, and acted as intermediaries for the English and American fur trade. They also developed skill as craftspeople in making clothing, baskets, tools, and architecture. Local indigenous populations were greatly reduced after forced displacement and disease, but a small Native American community persists in Multnomah County.The Portland area has historically been a center for trade since the city was founded in 1845. With time, commerce has diversified. Iron mining and smelting was common between 1867 and 1894, with paper mills becoming established as an industry in 1885. Plants manufacturing cement and conducting aluminum reduction, and shipyards can be found in the region. Industrial chemical production represents an important industry in Portland. Most of these industries rely on resources outsourced from other areas, except for the paper industry; business is driven by low power costs and the local industrial mineral market. Other important manufacturing industries in the nearby region include food processing and logging.
In 1893, the Kelly Butte Natural Area was designated upon a petition from the Portland City Council. Named after a pioneer family, the park covers an area of, including part of the Boring Lava Field, on public land to the southeast of downtown Portland, Historically, it sustained a quarry, prompting the creation of the Kelly Butte Jail, which used prisoner labor to gather crushed rocks for building roads in Portland until the 1950s. In general, rocks from the Boring Lava Field have been used for masonry projects including retaining walls, garden walls, and rock gardens, especially oxidized and scoriaceous rocks. Despite the prevalence of quarrying activity in historical times, there is no ongoing mineral or aggregate resource mining near the Boring Lava Field.
In 1952, after a local vote, the Kelly Butte Civil Defense Center was built between 1955 and 1956, costing about $670,000. The center was constructed to host local government agents should a nuclear attack on Portland occur; it had an area of, intended to host 250 people in case an emergency government became necessary. It was known throughout the United States as a model facility for local governments, and in 1957, the docudrama A Day Called X included footage of the Defense Center. The center was left obsolete after a 1963 Portland City Council vote to abolish it passed; in 1968, just one permanent employee remained. Eventually the building was converted into an emergency services dispatch center from 1974 through 1994, when it was abandoned due to rising costs for renovation and space limitations. That same year the building was vacated, and then it was sealed off in 2006. A sixty-bed isolation hospital operated at Kelly Butte from September 1920 until 1960, supporting patients with communicable disease. A water tank stood in the area from 1968 through 2010, when it was replaced with a underground reservoir that cost $100million, despite opposition from local environmental groups like the Friends of the Reservoirs. Historically, the park has also housed a police firing range, and Kelly Butte remains a recreational space today, administered jointly by Portland Parks and Recreation and the Portland Water Board.
In 1981, the Portland city government built a reservoir at the north end of Powell Butte, which still serves the city. In 1987, Portland government created Powell Butte Nature Park, covering of meadows and forest within the city. Planning started in 1995 for a second water reservoir in the area, which was built between 2011 and 2014. The new reservoir is underground, buried under topsoil and native plants, and it has a volume of. With the new reservoir came improvements to the Powell Butte park, including resurfaced and realigned trails, reduced environmental impacts, better accessibility measures, and reduction of steep grades. The government also built a visitor center, caretaker's house, public restrooms, maintenance yard, and a permeable parking area that permitted filtration of rainwater through asphalt to an underground stone bed, where it could be absorbed by the soil and then into the nearest aquifer.
Built between 1993 and 1998, the Robertson Tunnel runs for through the Tualatin Mountains. It contains Washington Park station, the deepest train station in North America, located underground. The station displays a core that exhibits Boring Lava deposits. For the first of the tunnel, the core shows Boring lava flows with cinder, breccia, and loess dated from 1.47million to 120,000 years ago, which have been deformed by the Sylvan fault. With the Oatfield fault, the Sylvan fault trends to the northwest, extending northwest and southeast of the tunnel. It is of Quaternary age and lacks surface expression, possibly as a result of its extensive burial by loess along its length.
In 2000, the nonprofit Friends of Mt. Tabor Park was formed to help maintain the Mount Tabor Park area, located east of downtown Portland. They have an organizational website and publish a bi-annual newsletter called the Tabor Times. Membership requires dues, and they also rely on donations and a gift shop for financial support.
In September 2017, the Hogan Butte Nature Park opened in the city of Gresham, encompassing an area of that includes the extinct Boring Lava Field volcano Hogan Butte. This park opened after more than 25 years of processing, supported by a 1990 bond from the city and two regional Metro bonds. Collaborators for opening the park include the U.S. Forest Service, local citizens, Metro, The Trust for Public Land, and the Buttes Conservancy organization. Gresham is one of just a few places in the United States with volcanoes contained in its city limits. Mount Sylvania and Mount Scott lie within the limits of Portland, in the southwestern and southeastern parts of the city, respectively.