The field lies within the Willamette National Forest near Santiam Pass. It supports some forested areas, which grow well on lava flows with tephra that serves as suitable soil for stands of Douglas fir and western hemlock and less commonly western red cedar. The surroundings represent an area of geological interest, and scoria has been quarried from one of the field's volcanic cones for highway supplies. Nearby tourist destinations include a ski resort, Tamolitch Falls, and Clear Lake.
The field borders Clear Lake, the source for the McKenzie River,[7] and lava flows from the field formed a dam that created the lake.[8] Clear Lake encompasses 148 acres (0.60km2)[9] near Oregon Route 126,[10] with a shallow northern region and a deeper southern zone, which reaches a maximum depth of 175 feet (53m).[9] Other nearby lakes include Lost Lake, Lava Lake, and Fish Lake. Fish Lake is an ephemeral lake that dries up during the summer season, formed by the damming of local water drainages by a lava flow from Sand Mountain Volcanic Field about 3,850 years ago.[11] Local topography has influenced eruptive activity in the past, directing lava flows downhill to the west and, with wind, directing tephra to the northeast.[7]
Annual precipitation in the Oregon Cascades averages 79 to 150 inches (2,000 to 3,800mm), with about 80percent falling in the winter season. In the High Cascades, discharge is steady throughout the year, and precipitation falls mostly as snow, which then melts, seeps into the ground, and reaches springs several years later.[12]
Ecology
The southern part of the field supports mature forests, but other zones with younger lava deposits are barren.[13] Mature forests correspond to lava flow areas with tephra; areas that do not have tephra cover lack soil and support only limited vegetation.[14] Below elevations of 4,300 feet (1,300m), these forests are typical of the lowlandtemperate climate of the Pacific Northwest, with Douglas fir and western hemlock predominating.[15] Notably, forests in the Sand Mountain volcanic field have fewer western red cedar trees than is common among other forests in the Pacific Northwest region.[7]Fen wetlands surround Lost Lake, which is about 3.1 miles (5km) north–northeast of the field.[16]
Within Clear Lake is a submerged forest of Douglas fir trees.[7] Well-preserved under 120 feet (37m) of water,[17] they can be seen standing on the bottom of the lake.[10] The cold water prevents most life from growing, giving the lake its name,[9] Analysis of samples from the underwater trees in 1965 suggested that the trees were "drowned" about 3,000 years ago, when a lava flow from Sand Mountain created Clear Lake.[18] The eruption altered the ecosystem and created new habitats in the lake, on its shores, and on the new lava flow deposits.[17] Today, life in the lake includes naturally reproducing fish species in Clear Lake such as brook and cutthroat trout, and the water is restocked annually with rainbow trout.[17]
Geology
The Cascade Range and Cascade Volcanic Arc result from the subduction of the Juan de Fuca tectonic plate under the North American tectonic plate.[19] In the Central Oregon Cascades, there are two subsegments: the Western Cascades (active from about 35 to 5 million years ago) and the High Cascades (active since 5 million years ago). As the North American Plate has rotated in a clockwise fashion above the subduction zone, volcanism has moved east in the central Oregon Cascades and moved west in the northern Cascades.[6]
The graben of the High Cascades is bounded to the east by the Green Ridge fault zone and to the west by the Horse Creek fault zone. It has a width of 19 miles (30km) and a depth of 1.2 to 1.9 miles (2 to 3km). Predominantly, it has generated mafic (rich in magnesium and iron) lava, producing about 14 cubic miles (60km3) of magma within the past 15,000 years. Moreover, many of the identified eruptive vents from the Quaternary include scoriacones or other mafic vents. The High Cascades graben displays a unique geochemical signature with low-Ktholeiite magma and a relatively enriched mantle source, produced by extension and heat flux.[6]
The Sand Mountain Volcanic Field was formed after magma entered rock that was fractured by faulting related to subsidence of the High Cascades graben. Beginning as dikes, these bodies of magma moved through conduits to separate volcanic vents at the surface. The initial magma was basaltic, though this was replaced several hundred years later by more evolved, basaltic andesite magma.[20] Eruptions at Sand Mountain Field were fed by two or three magma chambers,[21] including a number of mafic magma sources over a brief span of distance and time.[22]
The Sand Mountain Volcanic Field includes 23 basalt and basaltic andesite cinder cones and associated lava flows,[5] which were produced by two roughly north–south trending[23] alignments of 42volcanic vents.[5] The two groups cross near the Sand Mountain cinder cone; their alignments imply the existence of complex volcanic dikes under the field.[1] Sand Mountain marks the largest cinder cone in the field, at a height of 820 feet (250m).[1] According to the Global Volcanism Program, the field includes six major clusters of volcanic vents, all pyroclastic cones. These are the Central Group, Little Nash Crater, Lost Lake Group, Nash Crater, Sand Mountain Cones, and South Group.[11] Slight variations in vent alignment within groups likely reflect the small differences in local tectonic stress fields.[23] There is also evidence of vent reoccupation, suggested by lava deposits in close proximity at the Old Wagon Road vent and Great Spring vent eruptive units; one of the Great Spring cones buries part of an Old Wagon Road vent.[24]
There are three major geochemical groups in the field: Sand, Lost Lake, and Nash. Together they amount to 13 eruptive units, three of which have not been associated with exposed volcanic vents and one cluster of volcanic cones that do not have associated lava flows. The Sand group includes five eruptive units, while the Nash and Lost Lake group both consist of four units.[25] The Jack Pine cone has no associated lava deposits, and the SnoPark lava unit has no associated volcanic vent.[25] These two deposits exhibit unique compositions; SnoPark lava has relatively higher levels of barium and potassium oxide than the rest of the field, with the exception of the Jack Pine lava, which has even higher concentrations of barium (and also very high levels of strontium),[26] at 1081ppm and 1343ppm, respectively.[27]
Single lava units at the field have uniform compositions, which is distinct from other young lava deposits within the surrounding region;[25] major distinguishing elements include silicon dioxide (silica), titanium dioxide, magnesium oxide, and calcium oxide.[28] The Sand group has high compositional variation, ranging from basalt to basaltic andesite,[28] while the Lost Lake group is mostly basalt,[29] and the Nash group is completely composed of basaltic andesite.[28] The Nash group shows distinctively high silica content and a unique ratio of iron(II) oxide to magnesium oxide, and the Lost Lake Group is distinguished by its lower iron(II) oxide to magnesium oxide ratio and high magnesium oxide content.[29]
According to Wood and Kienle (1993), the field has a lava composition of subalkaline basalt and basaltic andesite.[5] Deligne et al (2016) argue that the field also has calc-alkaline basalt.[25] Morphologically, Sand Mountain Field lavas have blocky appearances,[26] reaching thicknesses up to 49 feet (15m)[30] though certain parts of the Lost Lake group have a ropy, pāhoehoe surface.[26]
Subfeatures
The Jack Pine cone in the Sand Mountain Field is composed of absarokites, which are unique within the Cascade Range. Its geochemical signature suggests that it was fed by a distinct magma chamber. Absarokites occur within the forearc of the Cascades and the Central Cascades, so this unique magma may be the result of old, metasomatized material from the Earth's mantle.[22]
The basaltic andesite at Little Nash Crater includes many small plagioclasephenocrysts with less abundant olivine phenocrysts, with silica levels of about 56.8percent. These flows are younger than 2,590 ± 150 years by radiocarbon dating.[31] Basaltic lava from the Lost Lake cone group contained 2–3percent olivine phenocrysts, which are slightly porphyritic; these deposits have been radiocarbon dated to 1,950 ± 150 years BP.[31] At Nash Crater, there are basaltic andesite lava flows with sparse olivine phenocrysts and silica levels of about 53.5percent.[31] The lava from the main Sand Mountain chain varies from 51.6–53.2percent silica, thus ranging from basalt to basaltic andesite in composition. Basalt lava at Sand Mountain contains sparse plagioclase and olivine phenocrysts, while basaltic andesite lava only exhibits olivine phenocrysts. These flows vary in age from are 3,850 ± 215 years BP to 2,750 years BP.[31]
The field also includes an extensive tephra deposit, which encompasses an area of 59 square miles (154km2) and has a volume of 0.094 cubic miles (0.39km3).[32] This tephra field is notable because it has a much greater volume and extent than tephra produced by other mafic volcanoes in the central Oregon Cascades.[33] Additionally, the tephra exhibits uniformity with a fine[34] mode grain size of 0.0049 inches (125μm) to 0.020 inches (0.5mm) and a lack of lapilli.[35] These tephra deposits vary in age from 3,440 ± 250 to 1,600 years BP, according to radiocarbon dating.[31] They reach thicknesses of greater than 6.6 feet (2m) as far as 5.6 miles (9km) from the Sand Mountain cinder cone and greater than 3.3 feet (1m) up to 7.5 miles (12km) from the cinder cone.[32]Microfractures within Sand Mountain clastic rock[36] along with the blocky, equant shapes and density of sideromelane and tachylite clastic rock in the field[37] suggest that Sand Mountain Field lava interacted with water.[38] According to McKay (2012), this likely came from groundwater.[39]
There is a lava tube called Lucy's Cavern that funneled the Sand Mountain Volcanic Field flows. It has a length of at least 490 feet (150m) and reaches depths of 26 to 33 feet (8 to 10m).[26] Its roof has a vaulted appearance with drip-like features.[40] There are also two circular "vertical pits" that reach depths of 62 feet (19m) and 98 feet (30m), respectively.[26] These open vertical conduit lava caves, known as Century and Moss Pits, lie to the southwest of Sand Mountain on a ridge of spatter material that trends to the east. There are also remnants of a third open conduit in a former vent, which left a crater about 30 feet (9.1m) in diameter. Both Moss Pit and Century Pit have vertical, circular entrances with smooth, remelted lining. Moss Pit has a diameter of 8 feet (2.4m) at the entrance, with a depth of 63 feet (19m). It also features a small chamber near its base, which slopes down for another 10 feet (3.0m). Century Pit lies 150 feet (46m) to the east of Moss Pit, with an entrance 3 feet (0.91m) in diameter. Surrounded by a wall of spatter material ranging from 1 to 2 feet (0.30 to 0.61m) in height, it has a vertical drop of 94 feet (29m), its lower half widening to a chamber with dimensions of 10 by 25 feet (3.0 by 7.6m) at its base. The western margin of the base has an opening about 6 feet (1.8m) deep, and at that depth it is blocked by debris. The lower chambers for both pits may be influenced by a fissure or may form part of an open fissure vent.[41]
Status as a volcanic field
Deligne et al. (2016) argue that "it is inarguably inappropriate" to consider Sand Mountain a volcanic field despite its official name.[24] They assert that Sand Mountain is a short-lived subfeature of a larger volcanic field of Quaternary volcanism in the region, which they refer to as the Central Oregon volcanic field.[42]
Eruptive history
During the Holocene epoch, volcanic activity has been particularly concentrated between the North Sister volcano and Three Fingered Jack, with at least 125 distinct eruptive centers active since the retreat of Pleistocene glaciers.[43] Eruptive activity in the upper McKenzie River catchment has been taking place since after the eruption of Mount Mazama about 7,700 years ago. Thus, it represents one of the youngest volcanic regions in the Cascade Arc. This activity is concentrated in the central Oregon Cascades, at the northwestern margin of the High Cascades graben near the boundary of the High Cascades and Western Cascades.[4]
The last eruption in the Sand Mountain Volcanic Field took place about 2,000 years ago at the Lost Lake cinder cone group, which lies at the northern–northeastern end of the field.[1] Before that, about 3,000 to 4,000 years ago, lava flows erupted from vents along the chain. They moved west and blocked drainage to create small lakes. Past lava flows from Sand Mountain and the nearby Belknap Crater historically disrupted the McKenzie River, producing highly fractured lava deposits across canyons, lakes, streams, and springs. They also produced the Sahalie Falls[1] and the Koosah Falls, as well as the 1.5-mile (2.4km) long Clear Lake, which still contains branches and bark from tree debris after the eruption.[44]
The overall dense-rock equivalent (DRE) volume for the volcanic field lavas and volcanic cones is estimated to be 0.22 to 0.29 cubic miles (0.9 to 1.2km3). The Sand group has a DRE volume of 0.15 cubic miles (0.64km3), Lost Lake a DRE volume of 0.072 cubic miles (0.3km3), and Nash group a DRE volume of 0.053 cubic miles (0.22km3).[21]
Past radiometric dating gave Sand Mountain Volcanic Field's age within a 1,000 year range. More precise paleomagnetic dating suggested that the field includes at least 13 distinct eruptive units, which were generated over a short period of time (likely just a few decades) about 2,950 years ago. The Jack Pine vent, which resides at the northern edge of the field, has a distinct composition from the field's other landforms; it likely erupted about 4,000 years prior to the rest of the field.[11] Deligne et al. (2016) agree with this age estimate, arguing that tephrochronology evidence and lava composition analysis suggest that Jack Pine erupted about 7,000 years ago, while the main Sand Mountain Volcanic Field eruptions took place circa 3,000 years ago.[45]
According to the Global Volcanism Program, a confirmed eruption dated to 950 BCE ± 200 years had a Volcanic Explosivity Index of 4, while another confirmed eruption at Jack Mountain dated to 5050 BCE had a Volcanic Explosivity Index of 2.[11] While geological evidence suggests that eruptions at Sand Mountain Field were explosive,[46] they differed from violent, Strombolian eruptions because their very explosive eruptions were sustained over a long period of time, likely partly attributable to interaction with water.[47] Walsh (2012) classifies the eruptions as sub-Plinian.[48][49]
The Nash Crater cinder cone erupted lava flows about 3,850 years ago, which coursed west and blocked a stream to create Fish Lake and Lava Lake. The lava flows were unvegetated and blocky.[11] According to Sherrod et al. (2004), these flows, also known as the Fish Lake lava flow, represent the oldest lava flows near the Santiam and McKenzie Passes after the cataclysmic eruption of Mount Mazama. Radiocarbon dating of a charred conifer branch found in Sand Mountain volcanic ash yielded an age of 3,440 ± 250 years Before Present (BP).[50] Radiocarbon dating of charcoal on a lateral moraine near Nash Crater gave an age of 2,590 ± 150 BP.[51] The Lost Lake cinder cones erupted about 1,950 years ago, along a fissure that trended from north to south near the northern end of the volcanic field. These eruptions blocked the Lost Creek tributary, forming Lost Lake.[11]
Future threats
The Sand Mountain Field is located 62 miles (100km) from a population of roughly 500,000 people.[11] It is close to a major transportation corridor from central Oregon to the Willamette Valley[52] as well as a popular ski area,[47] and future eruptions could have "substantial societal consequences" according to Deligne et al. (2016).[52] Lava flows from an eruption in the surrounding Central Oregon volcanic field could reach highways, but most mafic volcanism in the region is unlikely to threaten transportation given the small number of local roads.[42] Tephra from eruptions at Sand Mountain could reach more than 6.2 miles (10km) from the vent, and if lava flows reached forested regions they could initiate forest fires.[42] However, according to the Volcano Hazards Program of the United States Geological Survey, the threat potential from the field is "Low/Very Low."[1]
Eruptive activity within the nearby Cascades Range is likely to resume. Deformation near the Three Sisters complex volcano suggests the presence of intrusive magma in the region, which could eventually lead to eruptions, though the intrusion appears to be currently stalled. Further magma intrusions could lead to eruptions that would create new cinder cones similar to those in the Sand Mountain Field.[53] Moreover, hazardous volcanic gases could accumulate after an eruption,[49] such as sulfur dioxide, hydrogen chloride, and hydrogen fluoride.[54]
Human history
The upper McKenzie River catchment is an area of interest for geological research. The first research there took place in 1929, headed by H. T. Stearns.[4][55] In 1957, H. Williams produced a reconnaissance geological map,[4] which was followed by further mapping by E. M. Taylor in 1965. Taylor's work determined the presence of 9lava units at Sand Mountain Volcanic Field and another lava unit from Belknap Crater.[4][56] A map published by Sherrod et al. (2004) built upon Taylor's studies.[4]
In November 1963, the United States Forest Service sent divers from the Whitewater Diver group from Eugene to obtain tree samples from Clear Lake using Aqua-Lung technology. Two samples were acquired from one tree section, both about 1 foot (0.30m) in diameter, at a depth of about 13 feet (4.0m).[18] Radiocarbon dating analysis[57] suggested that the samples were dated to 3,200 ± 220 and 2,705 ± 200 years Before Present, respectively;[18] radiocarbon dating performed by Licciardi et al. (1999) found a similar result of 2750 ± 45 years Before Present.[58] Later radiocarbon dating of a conifer branch and charcoal on a lateral moraine near Nash Crater in 2004 had respective estimates of 3,440 ± 250 and 2,590 ± 150 years Before Present.[51]
Red and oxidized scoria has been quarried from Little Nash Crater for highway supplies near Santiam Pass.[11] The Carmen Smith Hydroelectric Power Scheme is fed by the upper McKenzie River and generates about 115 horsepower (86kW) of electricity.[6]
Recreation
The upper McKenzie River catchment area includes Clear Lake and Tamolitch Pool, which represent popular tourist locations.[6] At Clear Lake, popular activities include canoeing, fishing, and non-motorized boating, with 34 campsites available at the Cold Water Cove Campground and a grocery store, tackle shop, and restaurant located at the adjacent Clear Lake Resort.[17]
Volcanic formations including lava flows within McKenzie Pass have historically attracted the attention of passing motorists.[10] There is also a ski resort at Santiam Pass.[6]
Related Research Articles
Volcanic cones are among the simplest volcanic landforms. They are built by ejecta from a volcanic vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature and size of the fragments ejected during the eruption. Types of volcanic cones include stratocones, spatter cones, tuff cones, and cinder cones.
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, it lies in the eastern segment of the central portion of the High Cascades, the eastern segment of the Cascade Range. The volcano lies at the northern end of the 15-mile (24 km) long Mount Bachelor Volcanic Chain, which underwent four major eruptive episodes during the Pleistocene and the Holocene. The United States Geological Survey considers Mount Bachelor a moderate threat, but Bachelor poses little threat of becoming an active volcano in the near future. It remains unclear whether the volcano is extinct or just inactive.
The Mono–Inyo Craters are a volcanic chain of craters, domes and lava flows in Mono County, Eastern California. The chain stretches 25 miles (40 km) from the northwest shore of Mono Lake to the south of Mammoth Mountain. The Mono Lake Volcanic Field forms the northernmost part of the chain and consists of two volcanic islands in the lake and one cinder cone volcano on its northwest shore. Most of the Mono Craters, which make up the bulk of the northern part of the Mono–Inyo chain, are phreatic volcanoes that have since been either plugged or over-topped by rhyolite domes and lava flows. The Inyo volcanic chain form much of the southern part of the chain and consist of phreatic explosion pits, and rhyolitic lava flows and domes. The southernmost part of the chain consists of fumaroles and explosion pits on Mammoth Mountain and a set of cinder cones south of the mountain; the latter are called the Red Cones.
The Lassen volcanic area presents a geological record of sedimentation and volcanic activity in and around Lassen Volcanic National Park in Northern California, U.S. The park is located in the southernmost part of the Cascade Mountain Range in the Pacific Northwest region of the United States. Pacific Oceanic tectonic plates have plunged below the North American Plate in this part of North America for hundreds of millions of years. Heat and molten rock from these subducting plates has fed scores of volcanoes in California, Oregon, Washington and British Columbia over at least the past 30 million years, including these in the Lassen volcanic areas.
Cinder Cone is a cinder cone volcano in Lassen Volcanic National Park within the United States. It is located about 10 mi (16 km) northeast of Lassen Peak and provides an excellent view of Brokeoff Mountain, Lassen Peak, and Chaos Crags.
Newberry Volcano is a large active shield-shaped stratovolcano located about 20 miles (32 km) south of Bend, Oregon, United States, 35 miles (56 km) east of the major crest of the Cascade Range, within the Newberry National Volcanic Monument. Its highest point is Paulina Peak. The largest volcano in the Cascade Volcanic Arc, Newberry has an area of 1,200 square miles (3,100 km2) when its lava flows are taken into account. From north to south, the volcano has a length of 75 miles (121 km), with a width of 27 miles (43 km) and a total volume of approximately 120 cubic miles (500 km3). It was named for the geologist and surgeon John Strong Newberry, who explored central Oregon for the Pacific Railroad Surveys in 1855.
Mount Jefferson is a stratovolcano in the Cascade Volcanic Arc, part of the Cascade Range in the U.S. state of Oregon. The second highest mountain in Oregon, it is situated within Linn County, Jefferson County, and Marion County and forms part of the Mount Jefferson Wilderness. Due to the ruggedness of its surroundings, the mountain is one of the hardest volcanoes to reach in the Cascades. It is also a popular tourist destination despite its remoteness, with recreational activities including hiking, backpacking, mountaineering, and photography. Vegetation at Mount Jefferson is dominated by Douglas fir, silver fir, mountain hemlock, ponderosa pine, lodgepole pine, and several cedar species. Carnivores, insectivores, bats, rodents, deer, birds, and various other species inhabit the area.
Mount Mazama is a complex volcano in the western U.S. state of Oregon, in a segment of the Cascade Volcanic Arc and Cascade Range. Most of the mountain collapsed following a major eruption approximately 7,700 years ago. The volcano is in Klamath County, in the southern Cascades, 60 miles (97 km) north of the Oregon–California border. Its collapse, due to the eruption of magma emptying the underlying magma chamber, formed a caldera that holds Crater Lake. Mount Mazama originally had an elevation of 12,000 feet (3,700 m), but following its climactic eruption this was reduced to 8,157 feet (2,486 m). Crater Lake is 1,943 feet (592 m) deep, the deepest freshwater body in the U.S. and the second deepest in North America after Great Slave Lake in Canada.
Three Fingered Jack is a summit of a shield volcano of the Cascade Range in the U.S. state of Oregon. Formed during the Pleistocene epoch, the mountain consists mainly of basaltic andesite lava and was heavily glaciated in the past. While other Oregon volcanoes that were heavily glaciated—such as Mount Washington and Mount Thielsen—display eroded volcanic necks, Three Fingered Jack's present summit is a comparatively narrow ridge of loose tephra supported by a dike only 10 feet (3.0 m) thick on a generally north–south axis. Glaciation exposed radiating dikes and plugs that support this summit. The volcano has long been inactive and is highly eroded.
Mount Washington is a deeply eroded volcano in the Cascade Range of Oregon. It lies within Deschutes and Linn counties and is surrounded by the Mount Washington Wilderness area.
Belknap Crater is a shield volcano in the Cascade Range in the U.S. state of Oregon. Located in Linn County, it is associated with lava fields and numerous subfeatures including the Little Belknap and South Belknap volcanic cones. It lies north of McKenzie Pass and forms part of the Mount Washington Wilderness. Belknap is not forested and most of its lava flows are not vegetated, though there is some wildlife in the area around the volcano, as well as a number of tree molds formed by its eruptive activity.
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 south and is dominated by six small shield volcanoes; these shields are topped by small spatter and cinder cones, and the field includes a number of subglacial volcanoes and tuyas. The northernmost peak in the field is Sawtooth Mountain and the southernmost is Red Mountain; its highest point is Lemei Rock at an elevation of 5,925 feet (1,806 m).
Pisgah Crater, or Pisgah Volcano, is a young volcanic cinder cone rising above a lava plain in the Mojave Desert, between Barstow and Needles, California in San Bernardino County, California. The volcanic peak is around 2.5 miles (4.0 km) south of historic U.S. Route 66-National Old Trails Highway and of Interstate 40, and west of the town of Ludlow. The volcano had a historic elevation of 2,638 feet (804 m), but has been reduced to 2,545 feet (776 m) due to mining.
Broken Top is a glacially eroded complex stratovolcano. It lies in the Cascade Volcanic Arc, part of the extensive Cascade Range in the U.S. state of Oregon. Located southeast of the Three Sisters peaks, the volcano, residing within the Three Sisters Wilderness, is 20 miles (32 km) west of Bend, Oregon in Deschutes County. Eruptive activity stopped roughly 100,000 years ago, and erosion by glaciers has since reduced the volcano's cone to where its contents are exposed. There are two named glaciers on the peak, Bend and Crook Glacier.
The Boring Lava Field is a 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 and adjacent southwest Washington. The field got its name from the town of Boring, Oregon, located 12 miles (20 km) southeast of downtown Portland. Boring lies southeast of the densest cluster of lava 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.
West Crater is a small lava dome with associated lava flows in southern Washington, United States. Located in Skamania County, it rises to an elevation of 4,131 feet (1,259 m), and forms part of the Cascade Volcanic Arc. It is also part of the Marble Mountain-Trout Creek Hill volcanic field, a little-known Quaternary volcanic field in the southern Cascades of Washington state. The area can be hiked, and can be accessed by roads in the Gifford Pinchot National Forest.
Black Crater is a shield volcano in the Western Cascades in Deschutes County, Oregon. Located near McKenzie Pass, the volcano has a broad conical shape with gentle slopes. The volcano likely formed during the Pleistocene and has not been active within the last 50,000 years. Eruptive activity at the volcano produced mafic lava flows made of basaltic andesite and olivine basalt; it also formed a number of cinder cones. A normal fault occurs on the western side of the volcano, trending north–south. The volcano has been eroded by glaciers, which carved a large cirque into the northeastern flank of the mountain, forming its current crater.
The Twin Buttes are two volcanic cinder cones located in the Cascade Mountain Range in Shasta County, California. They are part of the Bidwell Spring chain and lie within a region that was active in the Quaternary. Formed during the Pleistocene between 25,000 and 15,000 years ago, the volcanoes erupted lava flows that coursed toward the Burney Mountain lava dome. These lava flows cover an area of 3.9 square miles (10.1 km2) and are made of basalt and dacite. The volcanoes also erupted cinder and volcanic ash that reached eastward.
Blue Lake Crater is a maar, or a broad, low-relief volcanic crater, in the U.S. state of Oregon. Located in Jefferson County, it consists of three overlapping craters, which hold Blue Lake. The drainage basin for Blue Lake has very steep, forested slopes and is mostly part of the explosion crater left by the volcano's eruption. The volcano lies within the Metolius River basin, which supports a wide array of plant life, large and small mammals, and more than 80 bird species. A 2009 Oregon law designated the Metolius River basin as an area of critical concern, preventing large-scale development and protecting wildlife.
Lunar Crater volcanic field is a volcanic field in Nye County, Nevada. It lies along the Reveille and Pancake Ranges and consists of over 200 vents, mostly small volcanic cones with associated lava flows but also several maars, including one maar named Lunar Crater. Some vents have been eroded so heavily that the structures underneath the volcanoes have been exposed. Lunar Crater itself has been used as a testing ground for Mars rovers and as training ground for astronauts.
Deligne, N. I.; Cashman, K. V.; Roering, J. J. (November 2013). "After the lava flow: The importance of external soil sources for plant colonization of recent lava flows in the central Oregon Cascades, USA". Geomorphology. 202: 15–32. Bibcode:2013Geomo.202...15D. doi:10.1016/j.geomorph.2012.12.009.
Deligne, N. I.; Conrey, R. M.; Cashman, K. V.; Champion, D. E.; Amidon, W. H. (November 1, 2016). "Holocene volcanism of the upper McKenzie River catchment, central Oregon Cascades, USA". GSA Bulletin. Geological Society of America. 128 (11–12): 1618–1635. Bibcode:2016GSAB..128.1618D. doi:10.1130/B31405.1.
Harris, S. L. (2005). "Chapter 13: The Three Sisters". Fire Mountains of the West: The Cascade and Mono Lake Volcanoes (Thirded.). Missoula, Montana: Mountain Press Publishing Company. pp.179–200. ISBN978-0-87842-511-2.
Walsh, L. K. (2012). Implications for volcanic hazards in the central and southern cascades based on gas emissions during explosive cinder cone activity (Thesis). University of Oregon.
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