DESCRIPTION:
Volcanic Fields and Lava Fields
Monogenetic Volcanic Fields - Mafic Volcanoes

Monogenetic volcanic fields are collections of cinder cones, and/or Maar vents and associated lava flows and pyroclastic deposits. Sometimes a stratovolcano is at the center of the field, as at the San Francisco Volcanic Field in Arizona. Monogenetic volcano fields have systematic growth patterns that suggest they represent single magmatic systems in the same way that stratovolcanoes do, but monogenetic volcanoes grow laterally rather than vertically (Wood and Shoan, 1984). Detailed mapping indicates that some cinder cones in monogenetic fields (e.g., Cima, California, and Timber Mountain Volcanic Field, Nevada) may have had multiple eruptions separated by tens to hundreds of thousands of years (Wells, et.al., 1989). Thus, some monogenetic cones may actually be polygenetic. This possibility differs from observations of historic eruptions (Wood, 1979), and is physically difficult to understand because cinder cone conduits are narrow and must solidify within a few years of eruption. Nonetheless, such multiple eruptions appear to have happened at least twice: Other cinder cones need to be closely reexamined.

Mafic volcanoes typically erupt less explosively than do composite volcanoes, so their eruption impacts are less widespread. Most mafic eruptions in the Three Sisters region have produced limited tephra deposits and lava flows that traveled typically 5-15 kilometers (3-9 miles) and rarely 15-20 kilometers (9-12 miles) from vents. Tephra deposits from such eruptions locally have thicknesses of several meters (6-12 feet) within 2 kilometers (1.2 miles) of vents, but seldom exceed 10 centimeters (4 inches) at distances 10 kilometers (6 miles) away from vents, and are typically much less. Some eruptions built scoria cones (piles of volcanic rubble centered around vents) with aprons of lava flows, like Pilot Butte in Bend. Others constructed broad shield volcanoes like Belknap Crater north of McKenzie Pass, which has lava flows that cover 100 square kilometers (40 square miles). At about 1,500 years old, Belknap Crater is one of the youngest mafic volcanoes in the Oregon Cascades. Some mafic eruptions constructed only a single small volcano, probably in a matter of days or weeks, while others involved eruptions along chains of several to tens of vents that may have continued for decades or centuries. The cluster of scoria cones and lava flows in the Sand Mountain area west of Santiam Pass was formed during three eruptive episodes between about 2,000 and 4,000 years ago. Mount Bachelor, a 1,000-meter-high (3,500 feet) mafic shield volcano, lies at the north end of a 25-kilometer-long (15 mile) chain of scoria cones and shield volcanoes that together cover 250 square kilometers (100 square miles). The entire chain formed over a period of several thousand years that ended about 12,000 years ago.

Monogenetic volcanoes typically erupt for only brief time intervals -- weeks to perhaps centuries -- and generally display a narrower range in eruptive behavior. Most monogenetic volcanoes are basaltic in composition, but just north of Mount Jefferson a few are of andesite and dacite composition -- that is, with a relatively higher silica content. Over a time span of hundreds of thousands of years, these monogenetic volcanoes have built a broad upland areas (hundreds to thousands of square kilometers (miles)) of mostly basaltic lava flows and small volcanoes. Prominent basaltic volcanoes in the Mount Jefferson region include Olallie Butte, Potato Butte, Sisi Butte, and North and South Cinder Peaks. Fresh-looking basalt lava flows can be seen along the Cabot Creek, Jefferson Creek, and upper Puzzle Creek drainages. Hundreds more basaltic volcanoes form the High Cascades of central Oregon to the south of Mount Jefferson, as far as Crater Lake, 180 kilometers (110 miles) away.

Amboy Crater - Lavic Lake Basalt Fields

• erupted approximately 10,000 years ago;
• consists of several mafic lava flows and cinder cones from several vents during the past approximately 10,000 years;
• volcanic domes: none recognized;
• mafic tephra erupted at several vents during the past approximate 10,000 years;
• pyroclastic flows: none recognized;
• blasts and pyroclastic surges: none recognized;
• debris avalanches and debris flows: none recognized;
• most recent eruption: mafic cinder cones and lava flows of apparent Holocene age (approximately 10,000 years ago);
• most probably future potential hazard (based on consideration of size, frequency, and severity of event): formation of cinder
• cones, small volumes of tephra, and lava flows; phreatic explosions.

Amboy Crater is a prominent, undissected cinder cone in the northeastern quadrant of the lava field. The volcano erupted along the northern border of Bristol Dry Lake and poured lava onto its surface, dividing it into the two present playas. The cone rises 75 meters above the surrounding lava flows and is approximately 460 meters in basal diameter. It is composed of a loose accumulation of volcanic ejecta with secondary amounts of agglutinated scoriaceous tephra plus ropy, ribbon- and almond-shaped bombs. Some lithic non-vesicular accessory basaltic ejecta are present, but included xenolithic fragments are absent. Amboy Crater is not a single cone but is composed of at least four nearby coaxial nested cones. The outer slopes of the main cone are gullied by erosion. Within the main outer cone, there is a remnant of a second cone on the west side; both cones are breached on the west. In addition to the two main cones, there are two relatively undisturbed cone walls within the main crater. These innermost cones are composed almost entirely of angular scoriaceous cinders.

Amboy Menu

Mount Wellington is the largest scoria cone (volume of scoria) and the second youngest volcano in the Auckland Volcanic Field, erupting about 9000 years ago. ... The Auckland Volcanic Field is comprised of monogenetic volcanoes which means it is unlikely that Mount Wellington or any of the existing volcanoes will erupt again. The next eruption will probably occur in a new location.

New Zealand Volcanoes and Volcanics Menu

Metropolitan Portland, Oregon, like Auckland, New Zealand, includes most of a Plio-Pleistocene volcanic field. The Boring Lava includes at least 32 and possibly 50 cinder cones and small shield volcanoes lying within a radius of 21 kilometers (13 miles) of Kelly Butte, which is 100 kilometers (62 miles) west of Mount Hood and the High Cascade axis -- (Web note: Kelly Butte is approximately 4 miles east of downtown Portland). Only the Clear Lake volcanics in California lie as far west in the coterminous United States. Unlike Clear Lake, Boring lava vents have been inactive for at least 300,000 years.

Within a 13-mile radius of Kelly Butte there are over 32 volcanic vents; within a 20-mile radius centered at Troutdale there are 90 volcanic centers. Most of these were originally small cinder cones like Pilot Butte and Lava Butte near Bend, Oregon, but some of them, such as Mount Sylvania in southwest Portland, Highland Butte 10 miles southeast of Oregon City, and Larch Mountain south of the Columbia River Gorge, were low, broad lava domes of the type called "shield volcanoes".

The densest concentration of volcanic vents lies west of the town of Boring, where 20 centers occur within an area of about 36 square miles. Because of this grouping near Boring, Ray Treasher (1942) first gave the name "Boring lava" to the lava, cinders, and ash which emanated from volcanic centers in the Portland area within a time span of from perhaps 10 million to less than 1 million years ago (Trimble, 1963). Some like Bob's Mountain in Washington, may be very young indeed.

"The Boring lava is composed mainly of basaltic flow rocks, but locally contains tuff-breccia, ash, tuff, cinders and scoriaceous phases" (Trimble, 1963). The Boring Lava, originating in the Portland area, is quite different from Yakima Basalt (Columbia River Basalt), which originated outside the area. The Boring, as compared to the Yakima, is gray rather than dark gray to black, and the jointing is generally massive or blocky rather than columnar or brickbat. Still more characteristic of the Boring Lava, as seen in thin section, is the meshwork of minute plagioclase laths (polotaxitic texture) commonly with open spaces between the laths (diktytaxitic texture). The Boring Lava contains olivine, rare in Yakima Basalt, and there is a very distinct geochemical difference between the two types of lavas (Beeson, personal commun., 1975).

Portland Area Volcanoes and Volcanics Menu

Boring Lava Field Menu

The Clear Lake volcanic field (late Pliocene to Holocene) lies in a tectonically active, complex geologic setting within the San Andreas transform fault system in northern Coast Ranges of California. Clear Lake and the volcanic field are located within a fault-bounded, locally extensional basin. The lake is the largest freshwater lake entirely within California; it is probably volcano-tectonic in origin, but is not a caldera lake. The volcanic field is the northernmost of a series of young Cenozoic volcanic fields in the Coast Ranges. Within the field, eruptive loci have migrated northward through the last 2.1 million years. Eruptive centers are lacking. Volcanism appears to be related to extension in a pull-apart basin within the San Andreas fault system and is not directly related to subduction, which ceased off the California coast at this latitude around 3 million years ago. ... Mount Konocti is the largest edifice of the Clear Lake volcanic field.

Clear Lake Menu

The Coso volcanic field is located at the west edge of the Basin and Range province. Initiation of volcanism at Coso preceded the onset of Basin and Range crustal extension there, as expressed by normal faulting. The earlier of the two principal periods of volcanism began with the emplacement of basalt flows over a surface of little relief. Then, during the ensuing period of approximately 1.5 million years, eruptive activity included chemically more evolved rocks erupted upon a faulted terrain of substantial relief. Following a 1.5-million-year hiatus with few eruptions, a bimodal field of basalt lava flows and rhyolite lava domes and flows developed on Basin and Range terrain of essentially the same form as today's landscape. Many of the young basalt flows are intercanyon, occupying parts of the present day drainage system.

The Coso volcanic field is best known for its Pleistocene rhyolite. Thirty-eight rhyolite domes and flows form an elongate array atop a north-trending 8 x 20-kilometer horst of Mesozoic bedrock. Nearby uneroded constructional forms are exhibited by most domes. Many are nested within tuff-ring craters, and a few filled and overrode their craters to feed flows a kilometer or two long. The two oldest domes contain several percent phenocrysts; the rest are essentially aphyric. Obsidian is exposed locally on most extrusions, and analyses of fresh glass indicate that all of the rhyolite is of the so-called high-silica variety; SiO2 content is essentially constant at 77 percent.

Coso Menu

Craters of the Moon lava field lies along the northern border of the Snake River Plain, midway between Arco and Carey, Idaho. It consists of Holocene to Pleistocene lava flows, cinder cones, spatter cones, lava tubes, and other features typical of basaltic volcanism. Much of the field lies within the Craters of the Moon National Monument, administered by the National Park Service.

The lava field covers, 1,600 square kilometers and consists of more than 60 mappable flows, around 25 cinder cones, and eight fissures/fissure systems. Detailed mapping and evaluation of dated flows have allowed USGS scientists to determine that the magma output rate was constant at around 1.5 cubic kilometers per 1000 years during 15,000-7,000 years B.P., then increased to 2.8 cubic kilometers per 1000 years from 7,000-2,000 years B.P.

Craters of the Moon Menu

During the past one million years, numerous volcanic vents were active throughout south-central Washington, from Vancouver to Goldendale. Most were probably active for relatively short times ranging from days to tens of years. Unlike Mount Adams, which has erupted repeatedly for hundreds of thousands of years, these vents typically did not erupt more than once. Rather, each erupting vent built a separate, small volcano, and over time a field of numerous overlapping volcanoes was created. Clusters of these vents define the Mount Adams, Indian Heaven, and Simcoe Mountains volcanic fields. In addition, the Goat Rocks volcanic center lies 30 kilometers (18 miles) north of Mount Adams. The Mount Adams and Indian Heaven fields have been the most active recently; the Simcoe field and the Goat Rocks center have not erupted for hundreds of thousands of years.

Because the numerous volcanoes in these fields were active for geologically brief times, they are much smaller than Mount Adams. Underwood Mountain, which lies west of the mouth of the White Salmon River, is one such volcano. It is about 8 kilometers (5 miles) in diameter and less than 800 meters (2,600 feet) high. About 9,000 years ago, the Big Lava Bed issued from a small volcano less than 300 meters (1,000 feet) high and partly filled the northwest part of the Little White Salmon River drainage basin with a thick lava flow almost 16 kilometers (10 miles) long. A few ancient lava flows were sufficiently large to flow down tributary valleys, spread out on the floor of the Columbia River Gorge, and dam the river to form a lake. The river then cut a new channel around or through the lava flow.

Mount Adams Volcanic Fields Menu

Composite volcanoes erupt episodically over tens to hundreds of thousand of years and can display a wide range of eruption styles. Mount Jefferson is a composite volcano that has been active episodically for about 300,000 years. Monogenetic volcanoes typically erupt for only brief time intervals -- weeks to perhaps centuries -- and generally display a narrower range in eruptive behavior. Most monogenetic volcanoes are basaltic in composition, but just north of Mount Jefferson a few are of andesite and dacite composition -- that is, with a relatively higher silica content. Over a time span of hundreds of thousands of years, these monogenetic volcanoes have built a broad upland areas (hundreds to thousands of square kilometers (miles)) of mostly basaltic lava flows and small volcanoes.

Monogenetic volcanoes typically erupt for only brief time intervals -- weeks to perhaps centuries -- and generally display a narrower range in eruptive behavior. Most monogenetic volcanoes are basaltic in composition, but just north of Mount Jefferson a few are of andesite and dacite composition -- that is, with a relatively higher silica content. Over a time span of hundreds of thousands of years, these monogenetic volcanoes have built a broad upland areas (hundreds to thousands of square kilometers (miles)) of mostly basaltic lava flows and small volcanoes. Prominent basaltic volcanoes in the Mount Jefferson region include Olallie Butte, Potato Butte, Sisi Butte, and North and South Cinder Peaks. Fresh-looking basalt lava flows can be seen along the Cabot Creek, Jefferson Creek, and upper Puzzle Creek drainages. Hundreds more basaltic volcanoes form the High Cascades of central Oregon to the south of Mount Jefferson, as far as Crater Lake, 180 kilometers (110 miles) away.

Mount Jefferson Menu

Mount Wellington is the largest scoria cone (volume of scoria) and the second youngest volcano in the Auckland Volcanic Field, erupting about 9000 years ago. ... The Auckland Volcanic Field is comprised of monogenetic volcanoes which means it is unlikely that Mount Wellington or any of the existing volcanoes will erupt again. The next eruption will probably occur in a new location.

New Zealand Volcanoes and Volcanics Menu

Metropolitan Portland, Oregon, like Auckland, New Zealand, includes most of a Plio-Pleistocene volcanic field. The Boring Lava includes at least 32 and possibly 50 cinder cones and small shield volcanoes lying within a radius of 21 kilometers (13 miles) of Kelly Butte, which is 100 kilometers (62 miles) west of Mount Hood and the High Cascade axis -- (Web note: Kelly Butte is approximately 4 miles east of downtown Portland). Only the Clear Lake volcanics in California lie as far west in the coterminous United States. Unlike Clear Lake, Boring lava vents have been inactive for at least 300,000 years.

Within a 13-mile radius of Kelly Butte there are over 32 volcanic vents; within a 20-mile radius centered at Troutdale there are 90 volcanic centers. Most of these were originally small cinder cones like Pilot Butte and Lava Butte near Bend, Oregon, but some of them, such as Mount Sylvania in southwest Portland, Highland Butte 10 miles southeast of Oregon City, and Larch Mountain south of the Columbia River Gorge, were low, broad lava domes of the type called "shield volcanoes".

The densest concentration of volcanic vents lies west of the town of Boring, where 20 centers occur within an area of about 36 square miles. Because of this grouping near Boring, Ray Treasher (1942) first gave the name "Boring lava" to the lava, cinders, and ash which emanated from volcanic centers in the Portland area within a time span of from perhaps 10 million to less than 1 million years ago (Trimble, 1963). Some like Bob's Mountain in Washington, may be very young indeed.

"The Boring lava is composed mainly of basaltic flow rocks, but locally contains tuff-breccia, ash, tuff, cinders and scoriaceous phases" (Trimble, 1963). The Boring Lava, originating in the Portland area, is quite different from Yakima Basalt (Columbia River Basalt), which originated outside the area. The Boring, as compared to the Yakima, is gray rather than dark gray to black, and the jointing is generally massive or blocky rather than columnar or brickbat. Still more characteristic of the Boring Lava, as seen in thin section, is the meshwork of minute plagioclase laths (polotaxitic texture) commonly with open spaces between the laths (diktytaxitic texture). The Boring Lava contains olivine, rare in Yakima Basalt, and there is a very distinct geochemical difference between the two types of lavas (Beeson, personal commun., 1975).

Portland Area Volcanoes and Volcanics Menu

Boring Lava Field Menu

Northern Arizona's San Francisco Volcanic Field, much of which lies within Coconino and Kaibab National Forests, is an area of young volcanoes along the southern margin of the Colorado Plateau. During its 6-million-year history, this field has produced more than 600 volcanoes. Their activity has created a topographically varied landscape with forests that extend from the Pinon-Juniper up to the Bristlecone Pine life zones. The most prominent landmark is San Francisco Mountain, a stratovolcano that rises to 12,633 feet and serves as a scenic backdrop to the city of Flagstaff.

The cones and lava flows of the San Francisco volcanic field, which covers about 2,000 square miles of the southwestern Colorado Plateau, result from several million years of volcanic activity. These powerful underground forces changed the landscape dramatically beginning in the winter of AD 1064-65. Sunset Crater appeared when molten rock sprayed out of a crack in the ground high into the air, solidified, then fell to earth as large bombs or smaller cinders.

Arizona Volcanoes and Volcanics Menu

Three Sisters is one of three potentially active volcanic centers that lie close to rapidly growing communities and resort areas in Central Oregon. Two types of volcanoes exist in the Three Sisters region and each poses distinct hazards to people and property. South Sister, Middle Sister, and Broken Top, major composite volcanoes clustered near the center of the region, have erupted repeatedly over tens of thousands of years and may erupt explosively in the future. In contrast, mafic volcanoes, which range from small cinder cones to large shield volcanoes like North Sister and Belknap Crater, are typically short-lived (weeks to centuries) and erupt less explosively than do composite volcanoes. Hundreds of mafic volcanoes scattered through the Three Sisters region are part of a much longer zone along the High Cascades of Oregon in which birth of new mafic volcanoes is possible. ...

Mafic volcanoes typically erupt for brief time intervals (weeks to perhaps centuries), but some can grow almost as large as composite volcanoes. Subsequent eruptions in the region typically issue from new vents and, over tens to hundreds of thousands of years, build broad fields of many volcanoes. Prominent mafic volcanoes in the Three Sisters region include North Sister, Mount Bachelor, Belknap Crater, Black Butte, and Mount Washington. Hundreds more mafic volcanoes form the High Cascades of central Oregon between the neighboring composite volcanoes of Mount Jefferson, 60 kilometers (40 miles) north of Three Sisters, Newberry volcano, a similar distance southeast, and Crater Lake, 120 kilometers (75 miles) south.

Mafic volcanoes typically erupt less explosively than do composite volcanoes, so their eruption impacts are less widespread. Most mafic eruptions in the Three Sisters region have produced limited tephra deposits and lava flows that traveled typically 5-15 kilometers (3-9 miles) and rarely 15-20 kilometers (9-12 miles) from vents. Tephra deposits from such eruptions locally have thicknesses of several meters (6-12 feet) within 2 kilometers (1.2 miles) of vents, but seldom exceed 10 centimeters (4 inches) at distances 10 kilometers (6 miles) away from vents, and are typically much less. Some eruptions built scoria cones (piles of volcanic rubble centered around vents) with aprons of lava flows, like Pilot Butte in Bend. Others constructed broad shield volcanoes like Belknap Crater north of McKenzie Pass, which has lava flows that cover 100 square kilometers (40 square miles). At about 1,500 years old, Belknap Crater is one of the youngest mafic volcanoes in the Oregon Cascades. Some mafic eruptions constructed only a single small volcano, probably in a matter of days or weeks, while others involved eruptions along chains of several to tens of vents that may have continued for decades or centuries. The cluster of scoria cones and lava flows in the Sand Mountain area west of Santiam Pass was formed during three eruptive episodes between about 2,000 and 4,000 years ago. Mount Bachelor, a 1,000-meter-high (3,500 feet) mafic shield volcano, lies at the north end of a 25-kilometer-long (15 mile) chain of scoria cones and shield volcanoes that together cover 250 square kilometers (100 square miles). The entire chain formed over a period of several thousand years that ended about 12,000 years ago.

Three Sisters Menu

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