HOME

TheInfoList



OR:

The Boring Lava Field (also known as the Boring Volcanic Field) is a
Plio-Pleistocene The Plio-Pleistocene is an informally described geological pseudo-period, which begins about 5 million years ago (Mya) and, drawing forward, combines the time ranges of the formally defined Pliocene and Pleistocene epochs—marking from about 5&n ...
volcanic field A volcanic field is an area of Earth's crust that is prone to localized volcanic activity. The type and number of volcanoes required to be called a "field" is not well-defined. Volcanic fields usually consist of clusters of up to 100 volcanoes ...
with
cinder cones A cinder cone (or scoria cone) is a steep conical hill of loose pyroclastic fragments, such as volcanic clinkers, volcanic ash, or scoria that has been built around a volcanic vent. The pyroclastic fragments are formed by explosive eruptions ...
, small shield volcanoes, and
lava flow Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...
s in the northern
Willamette Valley The Willamette Valley ( ) is a long valley in Oregon, in the Pacific Northwest region of the United States. The Willamette River flows the entire length of the valley and is surrounded by mountains on three sides: the Cascade Range to the eas ...
of the U.S. state of
Oregon Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...
and adjacent southwest
Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered o ...
state. The field got its name from the town of
Boring, Oregon Boring is an unincorporated community in Clackamas County, Oregon, United States. It is located along Oregon Route 212 in the foothills of the Cascade mountain range, approximately southeast of downtown Portland, and northeast of Oregon City. ...
, located southeast of downtown Portland. Boring lies southeast of the most dense cluster of lava 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 Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
, but the field itself is not. The volcanic field covers an area of about , and it has a total volume of . This region sustains diverse flora and fauna within its habitat areas, which are subject to Portland's moderate climate with variable temperatures and mild precipitation. The highest elevation of the field is at Larch Mountain, which reaches a height of . The
Portland metropolitan area The Portland metropolitan area is a metro area in the U.S. states of Oregon and Washington centered on the principal city of Portland, Oregon. The U.S. Office of Management and Budget (OMB) identifies it as the Portland–Vancouver–Hillsboro, ...
, including suburbs, is one of the few places in the continental United States to have extinct volcanoes within a city's limits, and the Boring Lava Field plays 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 Portland–Vancouver metropolitan area is very low. Boring Lava may also influence future earthquakes in the area, as
intrusive rock Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form '' intrusions'', such as batholiths, dikes, sills, laccoliths, and volcanic necks.Intrusive RocksIntrusive rocks accessdate: March ...
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 Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...
. 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 lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Li ...
. The Boring Lava deposits lie west of the town of Boring. The
Global Volcanism Program The Smithsonian Institution's Global Volcanism Program (GVP) documents Earth's volcanoes and their eruptive history over the past 10,000 years. The mission of the GVP is to document, understand, and disseminate information about global volcanic a ...
lists the volcanic field's highest
elevation The elevation of a geographic location is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface (see Geodetic datum § ...
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 distinguishing between Boring deposits and those from the major Cascade arc are less clear; many geologists have arbitrarily placed the eastern border at a longitude of 122 degrees 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
terrace Terrace may refer to: Landforms and construction * Fluvial terrace, a natural, flat surface that borders and lies above the floodplain of a stream or river * Terrace, a street suffix * Terrace, the portion of a lot between the public sidewalk an ...
s 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 The Columbia River ( Upper Chinook: ' or '; Sahaptin: ''Nch’i-Wàna'' or ''Nchi wana''; Sinixt dialect'' '') is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia ...
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 Pudding is a type of food. It can be either a dessert or a savoury (salty or spicy) dish served as part of the main meal. In the United States, ''pudding'' means a sweet, milk-based dessert similar in consistency to egg-based custards, inst ...
, Molalla, Tualatin, Abernethy, and Clackamas Rivers; tributaries for the Columbia River include the Washougal and
Sandy Rivers The US sitcom '' How I Met Your Mother'' premiered on CBS on September 19, 2005. Created by Craig Thomas and Carter Bays, the show is presented from the perspective of Ted Mosby in 2030 ("Future Ted") as he tells his children how he met the tit ...
. 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 Soil mechanics is a branch of soil physics and applied mechanics that describes the behavior of soils. It differs from fluid mechanics and solid mechanics in the sense that soils consist of a heterogeneous mixture of fluids (usually air and wat ...
from the local
aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characte ...
. This unit, part of the greater Troutdale
sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicat ...
aquifer, is also made of sandstone and conglomerate and bears water well. It also supplies water to domestic wells in the Mount Norway area. Boring Lava is known to have formed intrusions into local
sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
, and thus it may guide flow of
groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit ...
locally. 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, however, 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 In meteorology, prevailing wind in a region of the Earth's surface is a surface wind that blows predominantly from a particular direction. The dominant winds are the trends in direction of wind with the highest speed over a particular point on ...
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 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 A secondary forest (or second-growth forest) is a forest or woodland area which has re-grown after a timber harvest or clearing for agriculture, until a long enough period has passed so that the effects of the disturbance are no longer evident. I ...
, featuring
gorse ''Ulex'' (commonly known as gorse, furze, or whin) is a genus of flowering plants in the family Fabaceae. The genus comprises about 20 species of thorny evergreen shrubs in the subfamily Faboideae of the pea family Fabaceae. The species are ...
,
huckleberry Huckleberry is a name used in North America for several plants in the family Ericaceae, in two closely related genera: '' Vaccinium'' and '' Gaylussacia''. The huckleberry is the state fruit of Idaho. Nomenclature The name 'huckleberry' is a ...
,
nettle {{redirect, Nettle Nettle refers to plants with stinging hairs, particularly those of the genus '' Urtica''. It can also refer to plants which resemble ''Urtica'' species in appearance but do not have stinging hairs. Plants called "nettle" includ ...
s,
poison oak Poison oak refers to two plant species in the genus ''Toxicodendron,'' both of which can cause skin irritation: *''Toxicodendron diversilobum'' or Western poison oak, found in western North America *''Toxicodendron pubescens ''Toxicodendron pub ...
,
salal ''Gaultheria shallon'' is an evergreen shrub in the heather family (Ericaceae), native to western North America. In English, it is known as salal, shallon, or (mainly in Britain) gaultheria. Description ''Gaultheria shallon'' is tall, spra ...
, and
blackberry The blackberry is an edible fruit produced by many species in the genus ''Rubus'' in the family Rosaceae, hybrids among these species within the subgenus ''Rubus'', and hybrids between the subgenera ''Rubus'' and ''Idaeobatus''. The taxonomy ...
. Myriad species of fern, as well as rapid-growth
deciduous In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, ...
trees like
alder Alders are trees comprising the genus ''Alnus'' in the birch family Betulaceae. The genus comprises about 35 species of monoecious trees and shrubs, a few reaching a large size, distributed throughout the north temperate zone with a few sp ...
and vine maple are also frequent. Forests support stands of
Douglas fir The Douglas fir (''Pseudotsuga menziesii'') is an evergreen conifer species in the pine family, Pinaceae. It is native to western North America and is also known as Douglas-fir, Douglas spruce, Oregon pine, and Columbian pine. There are three v ...
,
western hemlock ''Tsuga heterophylla'', the western hemlock or western hemlock-spruce, is a species of hemlock native to the west coast of North America, with its northwestern limit on the Kenai Peninsula, Alaska, and its southeastern limit in northern Sonoma ...
,
western redcedar ''Thuja plicata'' is an evergreen coniferous tree in the cypress family Cupressaceae, native to western North America. Its common name is western redcedar (western red cedar in the UK), and it is also called Pacific redcedar, giant arborvitae, w ...
,
Pacific dogwood ''Cornus nuttallii'', the Pacific dogwood, western dogwood, or mountain dogwood, is a species of dogwood tree native to western North America. Description It is a small to medium-sized deciduous tree, reaching tall, often with a canopy spre ...
,
bigleaf maple ''Acer macrophyllum'', the bigleaf maple or Oregon maple, is a large deciduous tree in the genus '' Acer''. It is native to western North America, mostly near the Pacific coast, from southernmost Alaska to southern California. Some stands are al ...
,
Oregon ash ''Fraxinus latifolia'', the Oregon ash, is a member of the ash genus ''Fraxinus'', native to western North America. Description ''Fraxinus latifolia'' is a medium-sized deciduous tree that can grow to heights of in height, with a trunk diamete ...
,
red alder ''Alnus rubra'', the red alder, is a deciduous broadleaf tree native to western North America (Alaska, Yukon, British Columbia, Washington, Oregon, California, Idaho and Montana). Description Red alder is the largest species of alder in ...
, cascara buckthorn,
Pacific madrone ''Arbutus menziesii'' or Pacific madrone (commonly madrone or madrona in the United States and arbutus in Canada), is a species of broadleaf evergreen tree in the family Ericaceae, native to the western coastal areas of North America, from Br ...
, 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 ''Populus trichocarpa'', the black cottonwood, western balsam-poplar or California poplar, is a deciduous broadleaf tree species native to western North America. It is used for timber, and is notable as a model organism in plant biology. ...
and red alder. Forest communities have many additional shrubs including Indian plum, western hazel, and
snowberry ''Symphoricarpos'', commonly known as the snowberry, waxberry, or ghostberry, is a small genus of about 15 species of deciduous shrubs in the honeysuckle family, Caprifoliaceae. With the exception of the Chinese coralberry, '' S. sinensis'', whi ...
. Ground layer plants include the
herbaceous Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials. Definitions of "herb" and "herbaceous" The fourth edition o ...
sword fern Sword fern is a common name for several ferns and may refer to: *''Nephrolepis'', a tropical genus of ferns, especially: **'' Nephrolepis exaltata'', commonly cultivated as a houseplant, including the Boston fern *''Polystichum'', a cosmopolitan ...
and
stinging nettle ''Urtica dioica'', often known as common nettle, burn nettle, stinging nettle (although not all plants of this species sting) or nettle leaf, or just a nettle or stinger, is a herbaceous perennial flowering plant in the family Urticaceae. ...
. In contemporary times, clearing of forests for housing development have left about half of the Boring Lava region still 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 Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
, with moderate to low flows and average gradients between 10 and 12 percent. Cool and clear, many sustain macroinvertebrates, and a smaller number support amphibians and fish. The
riparian zone A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the terrestrial biomes of the Earth. Plant habitats and communities along the river margins and banks a ...
s 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 The United States Fish and Wildlife Service (USFWS or FWS) is an agency within the United States Department of the Interior dedicated to the management of fish, wildlife, and natural habitats. The mission of the agency is "working with othe ...
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: white top 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 flycatcher The willow flycatcher (''Empidonax traillii'') is a small insect-eating, neotropical migrant bird of the tyrant flycatcher family. There are four subspecies of the willow flycatcher currently recognized, all of which breed in North America (in ...
s,
long-eared myotis The long-eared myotis (''Myotis evotis'') is a species of vesper bat in the suborder Microchiroptera. It can be found in western Canada, the western United States, and Baja California in Mexico Mexico ( Spanish: México), officially the U ...
es, fringed myotises,
long-legged myotis The long-legged myotis (''Myotis volans'') is a species of vesper bat that can be found in western Canada, Mexico, and the western United States. Description ''Myotis volans'' is a species of bat found in Order Chiroptera, Family Vespertillio ...
es,
Yuma myotis The Yuma myotis (''Myotis yumanensis'') is a species of vesper bat native to western North America. Description The Yuma myotis is a relatively small myotis, measuring in head-body length, with an average wingspan of and a weight of about . T ...
es, Pacific western big-eared bats, and
northern red-legged frog The northern red-legged frog (''Rana aurora'') is a species of amphibian, whose range is the coastal region stretching from southwest British Columbia to southern Mendocino County in Northern California, and is protected in Oregon and Califor ...
s have been identified as species of concern;
pileated woodpecker The pileated woodpecker (''Dryocopus pileatus'') is a large, mostly black woodpecker native to North America. An insectivore, it inhabits deciduous forests in eastern North America, the Great Lakes, the boreal forests of Canada, and parts of the ...
s,
bald eagle The bald eagle (''Haliaeetus leucocephalus'') is a bird of prey found in North America. A sea eagle, it has two known subspecies and forms a species pair with the white-tailed eagle (''Haliaeetus albicilla''), which occupies the same niche as ...
s,
cutthroat trout The cutthroat trout is a fish species of the family Salmonidae native to cold-water tributaries of the Pacific Ocean, Rocky Mountains, and Great Basin in North America. As a member of the genus '' Oncorhynchus'', it is one of the Pacific t ...
, and
coho salmon The coho salmon (''Oncorhynchus kisutch;'' Karuk: achvuun) is a species of anadromous fish in the salmon family (biology), family and one of the five Pacific salmon species. Coho salmon are also known as silver salmon or "silvers". The scientif ...
are also considered sensitive.


History

The nearby Portland area was inhabited by the
Chinook people Chinookan peoples include several groups of Indigenous people of the Pacific Northwest in the United States who speak the Chinookan languages. Since at least 4000 BCE Chinookan peoples have resided along the Lower and Middle Columbia River (W ...
, 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 Meriwether Lewis (August 18, 1774 – October 11, 1809) was an American explorer, soldier, politician, and public administrator, best known for his role as the leader of the Lewis and Clark Expedition, also known as the Corps of Discovery, wit ...
and
William Clark William Clark (August 1, 1770 – September 1, 1838) was an American explorer, soldier, Indian agent, and territorial governor. A native of Virginia, he grew up in pre-statehood Kentucky before later settling in what became the state of Miss ...
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 Material culture is the aspect of social reality grounded in the objects and architecture that surround people. It includes the usage, consumption, creation, and trade of objects as well as the behaviors, norms, and rituals that the objects crea ...
. 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 it 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 Kelly Butte Natural Area is a city park of about in southeast Portland in the U.S. state of Oregon, just east of Interstate 205. The park is named after pioneer Clinton Kelly, who settled the area east of the Willamette River in 1848. It is par ...
was formed by a petition from the Portland City Council. The park, a sect of public land to the southeast of downtown Portland named after a pioneer family, covers an area of , including part of the Boring Lava Field. Historically, it sustained a
quarry A quarry is a type of open-pit mine in which dimension stone, rock, construction aggregate, riprap, sand, gravel, or slate is excavated from the ground. The operation of quarries is regulated in some jurisdictions to reduce their envir ...
, prompting the creation of the Kelly Butte Jail, which used prisoner labor (under guard supervision) 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 Masonry is the building of structures from individual units, which are often laid in and bound together by mortar; the term ''masonry'' can also refer to the units themselves. The common materials of masonry construction are bricks, building ...
projects including
retaining wall Retaining walls are relatively rigid walls used for supporting soil laterally so that it can be retained at different levels on the two sides. Retaining walls are structures designed to restrain soil to a slope that it would not naturally keep to ...
s, garden walls, and
rock garden A rock garden, also known as a rockery and formerly as a rockwork, is a garden, or more often a part of a garden, with a landscaping framework of rocks, stones, and gravel, with planting appropriate to this setting. Usually these are small ...
s, especially oxidized and
scoria Scoria is a pyroclastic, highly vesicular, dark-colored volcanic rock that was ejected from a volcano as a molten blob and cooled in the air to form discrete grains or clasts.Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds. (2005) '' ...
ceous 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 Docudrama (or documentary drama) is a genre of television and film, which features dramatized re-enactments of actual events. It is described as a hybrid of documentary and drama and "a fact-based representation of real event". Docudramas typic ...
''
A Day Called X ''The Day Called 'X is a dramatized CBS documentary film set in Portland, Oregon, in which the entire city is evacuated in anticipation of a nuclear air raid, after Soviet bombers had been detected by radar stations to the north; it details the ...
'' 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 A fever hospital or isolation hospital is a hospital for infectious diseases such as scarlet fever and smallpox. Their purpose is to treat affected people while isolating them from the general population. Early examples included the Liver ...
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 $100 million, 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 (part of the Boring Lava Field), 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. Located underground, it is the deepest train station in North America. The tunnel 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 Loess (, ; from german: Löss ) is a clastic, predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust. Ten percent of Earth's land area is covered by loess or similar deposits. Loess is a periglacial or aeoli ...
dated from 1.47 million 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 The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million year ...
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 The United States Forest Service (USFS) is an agency of the U.S. Department of Agriculture that administers the nation's 154 national forests and 20 national grasslands. The Forest Service manages of land. Major divisions of the agency inc ...
, local citizens, Metro,
The Trust for Public Land The Trust for Public Land is a U.S. nonprofit organization with a mission to "create parks and protect land for people, ensuring healthy, livable communities for generations to come". Since its founding in 1972, the Trust for Public Land has compl ...
, 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.


Geology

There are 90 volcanic centers within a radius of Troutdale and more than 32 vents within a radius of Kelly Butte. Mostly small
cinder cone A cinder cone (or scoria cone) is a steep conical hill of loose pyroclastic fragments, such as volcanic clinkers, volcanic ash, or scoria that has been built around a volcanic vent. The pyroclastic fragments are formed by explosive eruption ...
vents, these volcanoes also include some larger
lava dome In volcanology, a lava dome is a circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Dome-building eruptions are common, particularly in convergent plate boundary settings. Around 6% of eruptions ...
s from
shield volcano A shield volcano is a type of volcano named for its low profile, resembling a warrior's shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more vi ...
es at Mount Sylvania, Highland Butte, and Larch Mountain. The Boring Lava Field marks the densest volcanic vicinity in this group, encompassing an area of . It includes more than 80 known small vents and associated lava flows, with more volcanic deposits likely present under sedimentary rock deposits from the Missoula Floods (also known as the Bretz or Ice Age Floods), which took place between 21,000 and 15,000 years ago and probably destroyed small cinder cones (including those made from
tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...
) and
maar A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption (an explosion which occurs when groundwater comes into contact with hot lava or magma). A maar characteristically fills with water to form a relatively shallo ...
craters, burying them under up to of
silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel ...
from
slack water Slack water is a short period in a body of tidal water when the water is completely unstressed, and there is no movement either way in the tidal stream, and which occurs before the direction of the tidal stream reverses. Slack water can be esti ...
. The Global Volcanism Program reports that the field includes somewhere between 32 and 50 shield volcanoes and cinder cones, with many vents concentrated northwest of the town of Boring.


Regional setting

Considered an outlier of the
Cascade Range The Cascade Range or Cascades is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, ...
, the Boring Lava Field lies about to the west of the major Cascade crest. It marks one of five volcanic fields along the Quaternary Cascade arc, along with
Indian Heaven Indian Heaven is a volcanic field in Skamania County in the state of Washington, in the United States. Midway between Mount St. Helens and Mount Adams, the field dates from the Pleistocene to the early Holocene epoch. It trends north to sout ...
, Tumalo in Oregon, the
Mount Bachelor Mount Bachelor, formerly named Bachelor Butte, is a dormant stratovolcano atop a shield volcano in the Cascade Volcanic Arc and the Cascade Range of central Oregon. Named Mount Bachelor because it stands apart from the nearby Three Sisters, ...
chain, and Caribou in California. Like the Cascade Range, the Boring field was also generated by the
subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, ...
of the oceanic Juan de Fuca tectonic plate under the North American tectonic plate, but it has a different tectonic position, with its eruptive activity more likely related to tectonic
rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-grabe ...
ing throughout the region. The Boring Lava Field has erupted material derived from hot
mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...
magma, and the subducting Juan de Fuca plate may be as shallow as in depth at their location. The High Cascades, a segment of the Cascade volcanic arc that includes the Boring Lava Field, is characterized by basaltic lava flows with andesite, tuff breccia, and volcanic ash. The High Cascades may lie over a
graben In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic conte ...
(a depressed block of the Earth's crust bordered by parallel faults), and activity at the Boring field and throughout the Portland area may be associated with deformation of the block. Portland lies within the Portland Basin, part of the
forearc Forearc is a plate tectonic term referring to a region between an oceanic trench, also known as a subduction zone, and the associated volcanic arc. Forearc regions are present along a convergent margins and eponymously form 'in front of' the v ...
(the region between an oceanic trench and the associated volcanic arc) between the Cascades major arc and the
Pacific Coast Ranges The Pacific Coast Ranges (officially gazetted as the Pacific Mountain System in the United States) are the series of mountain ranges that stretch along the West Coast of North America from Alaska south to Northern and Central Mexico. Although the ...
, which consist of Eocene to Miocene marine sedimentary rock deposits and Eocene intrusions and extrusions of basalt that were emplaced on the Siletz terrane. The eastern boundary for the Portland Basin is the Cascades, while the
Tualatin Mountains The Tualatin Mountains (also known as the West Hills or Southwest Hills of Portland) are a range on the western border of Multnomah County, Oregon, United States. A spur of the Northern Oregon Coast Range, they separate the Tualatin Basin of Was ...
lie to the west, along an
anticline In structural geology, an anticline is a type of fold that is an arch-like shape and has its oldest beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex up in which the hinge or crest is t ...
formation that has been changing since the Miocene. The Boring Lava Field sits on the floor of the Portland Basin, residing in the forearc setting between tectonic extension to the south and compression to the north. The uneven distribution of vents within this forearc suggests a local zone of crustal expansion. Over the last 2.7 million years, the volcanic field has irregularly rotated clockwise and migrated to the northwest at an average rate of ± per year relative to the surrounding crust. This northwest trending is consistent with other faults in the nearby area. The Boring Lava Field represents the youngest episode of volcanism within the Cascade forearc, and while there is no evidence that they were associated with a
slab window In geology, a slab window is a gap that forms in a subducted oceanic plate when a mid-ocean ridge meets with a subduction zone and plate divergence at the ridge and convergence at the subduction zone continue, causing the ridge to be subducted. ...
(a gap that forms in a subducted oceanic plate when a
mid-ocean ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a div ...
meets with a subduction zone and plate divergence at the ridge and convergence at the subduction zone continue, causing the ridge to be subducted), they likely interacted with the regional
mantle wedge A mantle wedge is a triangular shaped piece of mantle that lies above a subducting tectonic plate and below the overriding plate. This piece of mantle can be identified using seismic velocity imaging as well as earthquake maps. Subducting oceanic ...
.


Composition and local setting

The Boring Lava Field shows a similar composition to the High Cascades that run through Oregon and southern Washington state, with
Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...
basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...
lava flow Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...
s and
breccias Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of d ...
. It was active during the late
Tertiary Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...
into the early Quaternary. Within the field, lava shows a diverse composition overall, varying from low- K,
tholeiitic The tholeiitic magma series is one of two main magma series in subalkaline igneous rocks, the other being the calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic magma ...
to high-K,
calc-alkaline The calc-alkaline magma series is one of two main subdivisions of the subalkaline magma series, the other subalkaline magma series being the tholeiitic series. A magma series is a series of compositions that describes the evolution of a mafic m ...
eruptive products. Some of the low-K tholeiite deposits likely originated from vents closer to the High Cascades, and they are overlain by Boring Lava materials. J. M. Shempert, a geologist at
Portland State University Portland State University (PSU) is a public research university in Portland, Oregon. It was founded in 1946 as a post-secondary educational institution for World War II veterans. It evolved into a four-year college over the following two dec ...
, proposed that mantle sources for the two different lava types may be different and that the calc-alkaline sources are more
refractory In materials science, a refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycrystalline, polyphase, ...
. Like the surrounding High Cascades, Boring Lava Field erupted lava made of
olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers qui ...
basalt and
basaltic andesite Basaltic andesite is a volcanic rock that is intermediate in composition between basalt and andesite. It is composed predominantly of augite and plagioclase. Basaltic andesite can be found in volcanoes around the world, including in Central Am ...
; these sub-alkaline basalts and basaltic andesite predominate among Boring Lava deposits. The olivine basalt deposits have fine to medium textures, and the basaltic andesite lava flow deposits have relatively little
pyroclastic rock Pyroclastic rocks (derived from the el, πῦρ, links=no, meaning fire; and , meaning broken) are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyrocl ...
in them, suggesting that
explosive eruption In volcanology, an explosive eruption is a volcanic eruption of the most violent type. A notable example is the 1980 eruption of Mount St. Helens. Such eruptions result when sufficient gas has dissolved under pressure within a viscous magma su ...
s were uncommon within the field. Dark gray to light gray in color, Boring Lava produces
columnar Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellula ...
and platy
joints A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw- ...
, which can be seen in Oregon east of Portland and in Clark County in Washington state. It is usually
phyric 300px, feldspathic phenocrysts. This granite, from the Switzerland">Swiss side of the Mont Blanc massif, has large white plagioclase phenocrysts, triclinic minerals that give trapezoid shapes when cut through). 1 euro coins, 1 euro coin (diameter ...
, though one sample from Rocky Butte consists of
labradorite Labradorite (( Ca, Na)( Al, Si)4 O8) is a calcium-enriched feldspar mineral first identified in Labrador, Canada, which can display an iridescent effect (schiller). Labradorite is an intermediate to calcic member of the plagioclase series. It ...
with olivine phenocrysts that have been transformed to iddingsite. The Boring Lava reaches thicknesses of more than . Boring Lava has a more
mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks in ...
(rich in magnesium in iron) composition than the nearby volcano
Mount Hood Mount Hood is a potentially active stratovolcano in the Cascade Volcanic Arc. It was formed by a subduction zone on the Pacific coast and rests in the Pacific Northwest region of the United States. It is located about east-southeast of Portl ...
, but they are similar in age. There is a small amount of andesite in the lavas from the field, mostly erupted from monogenetic vents or Larch Mountain. Sometimes, Boring Lava overlaps with volcaniclastic conglomerate from other Cascade eruptions in
Multnomah County Multnomah County is one of the 36 counties in the U.S. state of Oregon. As of the 2020 census, the county's population was 815,428. Multnomah County is part of the Portland–Vancouver– Hillsboro, OR–WA Metropolitan Statistical Area. Th ...
and the northern part of
Clackamas County Clackamas County is one of the 36 counties in the U.S. state of Oregon. As of the 2020 census, the population was 421,401, making it Oregon's third-most populous county. Its county seat is Oregon City. The county was named after the Nati ...
. The Boring Lava also contains tuff, cinder, and scoria; it is characterized by
plagioclase Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more p ...
laths that show a pilotaxitic texture with spaces between them that show a diktytaxitic texture. The Boring Lava exposures show aeromagnetic anomalies with short wavelengths and high amplitudes suggestive of their relatively young geological ages. At points where the Boring Lava sits over Troutdale Formation deposits, landslides are frequent, producing steep head scarps with heights of up to . These scarps tend to have grabens at their bases and Boring Lava blocks at their tops, and they show variable slide surfaces from hummocky to flat. A number of these exposures show dips up to 35 degrees, as well as minor faults. The landslides range in thickness from . Portland's wet climate leads to
weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs '' in situ'' (on site, with little or no movement ...
, which at the Boring Lava Field has reached depths of up to , altering the upper of soil to a red, clay-like material. At the cinder cone in Mount Tabor Park, an
outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. Features Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficia ...
of
quartzite Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tec ...
-pebble
xenolith A xenolith ("foreign rock") is a rock fragment ( country rock) that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term ''xenolith'' is almost exclusively used to describe inclusions in ig ...
s (rock fragments enveloped in a larger rock during the latter's development and solidification) can be observed among local cinder specimens, dating from Miocene to Pliocene Troutdale deposits. While the volcanic rock of Boring Lava was being emplaced over rock from the Troutdale formation, there was
deformation Deformation can refer to: * Deformation (engineering), changes in an object's shape or form due to the application of a force or forces. ** Deformation (physics), such changes considered and analyzed as displacements of continuum bodies. * Defor ...
that
uplifted ''Uplifted'' is the second studio album by Nigerian singer Flavour N'abania. It was released on July 20, 2010, by Obaino Music and 2nite Entertainment. The album features guest appearances from Jay Dey, Oloye, Stormrex, Waga Gee, Asemstone, M-Jay, ...
and dropped fault blocks to the southeast of Portland. Along the Washougal River, a large
landslide Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated slope failures, mudflows, and debris flows. Landslides occur in a variety of environmen ...
occurred as a result of
failure Failure is the state or condition of not meeting a desirable or intended objective, and may be viewed as the opposite of success. The criteria for failure depends on context, and may be relative to a particular observer or belief system. One ...
due to the Boring Lava pushing down on rock from the Troutdale formation. Intrusions of Boring Lava formed outcrops at Highland Butte, La Butte, and potentially in the subsurface regions near
Aurora An aurora (plural: auroras or aurorae), also commonly known as the polar lights, is a natural light display in Earth's sky, predominantly seen in high-latitude regions (around the Arctic and Antarctic). Auroras display dynamic patterns of bri ...
and Curtis, and these intrusions have been associated with normal faulting at Parrett and Petes Mountain, Aurora, Curtis, and Swan Island (along the Molalla River). Faults together with igneous intrusions are usually accompanied by stretching and doming as a result of magma influxes or collapses from the evacuation of the magma flows. Similarly, faults north of Oregon City might have resulted from subsidence after magma chambers emptied or lava was extruded as a result of Boring Lava eruptions. Some of the Boring Lava vents cut off hydrogeologic units in the surrounding area. Eruptive vents on the western edge of the field formed along a fault line that trended to the northeast, located north of present-day Carver. Boring Lava was erupted by vents in the volcanic field, and it has been exposed at elevated topographic levels in intact volcanic cones and dissected lava plains. There is likely more lava deposited under Quaternary sedimentary mantle throughout the region, though activity was confined to a relatively concentrated area.


Subfeatures

D. E. Trimble (1963) argued that the Boring Lava Field was produced by eruptive activity at 30 volcanic centers; these include shield and cinder cone volcanoes. J. E. Allen reported 95 vents in 1975, dividing them into four clusters: 17 vents north of the Columbia River, 14 vents west of the Willamette River, 19 vents east of the Willamette River and north of Powell Valley Road, and 45 vents east of the Willamette River and south of Powell Valley Road (Highway 26). Of these, 42 were unnamed, and several volcanoes contained multiple vents. Generally, all lava flows in the field can be traced to specific vents in the field, but documented source vents have mostly been confirmed through chemical analysis or petrographic comparisons, with a few exceptions. In the eastern part of the Boring cluster, volcanic vents have average diameters less than , with average heights less than from base to summit. The lava flows from Highland Butte and Larch Mountain, both shield volcanoes, encompass a wide area, the Boring Lava deposits averaging thicknesses of not considering areas next to volcanic cones in the field. Most of the summit craters have been destroyed, though there are partial craters at Bobs Hill (located northeast of Portland) and Battle Ground Lake (located north of Portland); Mount Scott also has an intact summit crater. However, many of the Boring vents retain the shape of a volcanic cone, with loess extending above an elevation of . The Rocky Butte plug, which reaches a height of above its surroundings, was dated to 125,000 ± 40,000 years old by R. Evarts and B. Fleck from the
United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...
(USGS). Mount Tabor is also prominent in the area, dated by the USGS to 203,000 ± 5,000 years old, as are Kelly Butte, Powell Butte, and Mount Scott. Scott has been dated to 1.6 million years ago. A series of
lava tube A lava tube, or pyroduct, is a natural conduit formed by flowing lava from a volcanic vent that moves beneath the hardened surface of a lava flow. If lava in the tube empties, it will leave a cave. Formation A lava tube is a type of lava ...
s were documented near the
Catlin Gabel School The Catlin Gabel School is an independent preschool through 12th grade institution located on 67 acres in Portland, Oregon 5 miles west of downtown. Annual enrollment is approximately 780 students from a wide variety of cultures, backgrounds, and ...
along the western slope of the Portland Hills. These formations, created by lava flows cooling at the surface while their hot interior kept draining, were first identified by R. J. Deacon in 1968, then analyzed by L. R. Squier in 1970; they were studied in greater detail by J. E. Allen and his team in 1974. The Catlin Gabel tubes lie among cinder cones and lava flows from the Pliocene to Pleistocene, and they are the oldest known lava tubes in Oregon, older than the Holocene. The tubes were produced by a small vent at the southern end of the northern segment of the field, extending from its base to the south and then the west. They originated from the uppermost lava flow from a series of eruptions that ran into a valley on the western slope of the Portland Hills. The Catlin Gabel tubes have a width of , with slopes averaging per mile for an average grade of 3 percent. On average, these tubes have a thickness of near their center, with an upper lava unit thickness of that has since been modified by erosion and the deposition of up to of Portland Hills silt. The Catlin Gabel tubes also sit atop of silt from the Troutdale Formation. Running along the tube's arc are five depressions, which were created through the collapsing roofs of the lava tubes within a subsegment that is in length. The characteristics of the tube system are not well documented, since only the collapsed segments are accessible. Some of the channels have been reduced to rubble, and analysis has revealed that they trended northwest, had widths up to and depths no more than , and required special engineering procedures to permit the construction of a 15-story building above them.


Oregon vents

The following vents are in Oregon:


Washington vents

The following vents are in Washington:


Eruptive history

Eruptions at Boring Lava Field occur in a concentrated manner, often in clusters of three to six vents, as at Bobs Mountain and Portland Hills. These types of vents typically produced similar types of magma in relatively short periods of time, and they also frequently show alignment. Vents in the field have generally produced basalt and basaltic andesite, with some andesitic eruptions, including those that produced the Larch Mountain shield volcano. Prior to the 1990s, there was little potassium-argon dating data available for the lava field, and despite the field's proximity to an urban area, little was known about its composition until recent years. Weathering, fine grain size, and glassy content further limit
argon–argon dating Argon–argon (or 40Ar/39Ar) dating is a radiometric dating method invented to supersede potassiumargon (K/Ar) dating in accuracy. The older method required splitting samples into two for separate potassium and argon measurements, while the newer ...
for the field. Recent argon–argon dating suggests that eruptive activity at the Boring Lava Field began between 2.6 and 2.4 million years ago, yielding far-reaching basalt lava flows, the Highland Butte shield volcano, a number of monogenetic vents, and one andesitic lava flow. These took place near the southern Portland Basin, and were followed by about 750,000 years of quiescence. About 1.6 million years ago, eruptive activity resumed to the north of the previously active area, with alkalic basalt lava flows generating the Mount Scott shield volcano. As eruptions shifted to the east over time, the Larch Mountain volcano was produced by eruptions in the foothills of the Cascade Range. Activity spread out over the area, extending to its current expansive state about one million years ago. In addition to spreading out geographically, the lava composition in the field's vents became more diverse. This period continued until about 500,000 years ago, with no activity until about 350,000 years ago, after which activity continued through roughly 60,000 to 50,000 years ago according to several sources, or about 120,000 years ago according to I. P. Madin (2009). R. Evarts and Fleck originally reported that lava flows at the Barnes Road deposit of the field represented the youngest eruptive products in the Boring area, with a
radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares ...
age of 105,000 ± 6,000 years. These eruptions followed a relatively even age distribution over time; younger vents and associated deposits lie in the northern portion of the field, while older deposits are confined to the south. The products of the Boring Lava Field were erupted discontinuously over an
erosion surface In geology and geomorphology, an erosion surface is a surface of rock (geology), rock or regolith that was formed by erosion and not by construction (e.g. lava flows, sediment deposition) nor fault (geology), fault displacement. Erosional surfaces ...
. Activity took place during the late Tertiary and early Quaternary, in what is now the Portland area as well as the surrounding area, with a particularly concentrated pocket of activity to the east. Nearly all of these eruptions were confined to single vents or small vent complexes, with the exception of a lava plain southeast of present-day Oregon City. Boring Lava generally consists of flowing lava; only one eruptive deposit contains tuff, ash, and tuff breccia, and one vent to the northeast of the Carver area displayed evidence of explosive eruptions that later became
effusive In physics and chemistry, effusion is the process in which a gas escapes from a container through a hole of diameter considerably smaller than the mean free path of the molecules. Such a hole is often described as a ''pinhole'' and the escape ...
.


Recent activity and current threats

Sometime less than 100,000 years ago, magma at Battle Ground Lake in Washington state interacted with water to form the eponymous maar volcano, destroying a lava flow dated to 100,000 years ago. The last volcanic center to form in the field was Beacon Rock, a cinder cone produced by eruptions about 57,000 years ago, which was eroded by the Missoula Floods to leave only its central
volcanic plug A volcanic plug, also called a volcanic neck or lava neck, is a volcanic object created when magma hardens within a vent on an active volcano. When present, a plug can cause an extreme build-up of high gas pressure if rising volatile-charged ma ...
. While the known volcanic vents in the Boring Lava Field are
extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
, the field itself is not considered extinct. However, the probability for future eruptions in the Portland–Vancouver metropolitan area is "very low". It is rare that more than 50,000 years pass without an eruption in the region; given the past eruptive history of the field, an eruption is predicted to occur once every 15,000 years on average. About half of the Boring Lava Field eruptions took place in what are today densely populated areas of the Portland–Vancouver metropolitan area. Though the formation of a small cinder cone vent might not extend far beyond its surroundings, depending on location, similar eruptions could lead to deposition of volcanic ash that could lead to serious infrastructural consequences, covering large areas. A larger eruption, like the ones that built Larch Mountain or Mount Sylvania, could span years to decades. It is unclear where exactly a future eruption might take place, but it would probably occur in the northern portion of the field. Many seismic faults in the northeastern section of the northern Willamette Valley formed as a result of intrusions of Boring Lava, as supported by their orientation, lengths, displacements, age, and proximity to Boring Lava intrusions. Though intrusions from any future eruptions at the Boring field are "probably minimal", Boring Lava might play a role in determining the intensity of ground shaking during future earthquakes in the area.


Recreation

Trails in the city of Gresham travel over parts of the Boring Lava Field and its cones. Mount Tabor and Powell Butte are better known for their recreational uses than other cones; Powell Butte Nature Park has of trails. The Mt. Tabor Park is open to bicyclists and pedestrians from 5 a.m. through midnight and to motorized vehicles from 5 a.m. through 10 p.m. each day, except for Wednesdays when the park roads are not open to automobiles. The Hogan Butte Nature Park offers views of Mount Adams, Mount Hood,
Mount Rainier Mount Rainier (), indigenously known as Tahoma, Tacoma, Tacobet, or təqʷubəʔ, is a large active stratovolcano in the Cascade Range of the Pacific Northwest, located in Mount Rainier National Park about south-southeast of Seattle. With a ...
, and Mount St. Helens, as well as running trails and sites for
picnic A picnic is a meal taken outdoors ( ''al fresco'') as part of an excursion, especially in scenic surroundings, such as a park, lakeside, or other place affording an interesting view, or else in conjunction with a public event such as preceding ...
king. In addition to the nature park on Hogan Butte, a number of smaller cinder cones are also publicly accessible. The Gresham Saddle Trail traverses Gresham Butte and Gabbert Butte, running for . The trail is considered to be of moderate difficulty, and it offers no amenities. It includes the Gabbert Loop Trail, which extends for through forests of maples, alders, ferns, and firs.


Notes

* Evarts et al. (2009) list only 80 centers but acknowledge there are likely more buried vents; Le Corvec et al. (2013) list 88 volcanic centers at Boring Lava Field. * Low-K is a geological term used to describe lava with low amounts of potassium, while high-K describes lava enriched in potassium. * Refractory refers to any material that does not easily convert from liquid to gas via the process of
vaporization Vaporization (or vaporisation) of an element or compound is a phase transition from the liquid phase to vapor. There are two types of vaporization: evaporation and boiling. Evaporation is a surface phenomenon, whereas boiling is a bulk phenomenon ...
, which includes elements and compounds made from metals.


References


Sources

* * *. * * . * * . * * * * * * * * . * * * * * . * . * * * * . * . * . * *


External links


USGS Map of Boring Lava Field
{{Volcanoes of Oregon Volcanic fields of Oregon Volcanic fields of Washington (state) Subduction volcanoes Cascade Volcanoes Extinct volcanoes Pliocene volcanism Pleistocene volcanism Lava fields Geography of Portland, Oregon