Sand Mountain Field
   HOME

TheInfoList



OR:

The Sand Mountain Volcanic Field (also known as the Sand Mountain Field) is a
volcanic field A volcanic field is an area of Earth's Earth's crust, crust that is prone to localized volcano, volcanic activity. The type and number of volcanoes required to be called a "field" is not well-defined. Volcanic fields usually consist of clusters ...
in the upper McKenzie River
watershed Watershed may refer to: Hydrology * Drainage divide, the line that separates neighbouring drainage basins * Drainage basin, an area of land where surface water converges (North American usage) Music * Watershed Music Festival, an annual country ...
, located in the
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
in
Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...
. Part of the
Cascade Volcanic Arc The Cascade Volcanoes (also known as the Cascade Volcanic Arc or the Cascade Arc) are a number of volcanoes in a continental volcanic arc in western North America, extending from southwestern British Columbia through Washington and Oregon to No ...
, it lies southwest of Mount Jefferson and northwest of
Belknap Crater 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 ...
and
Mount Washington Mount Washington is an ultra-prominent mountain in the state of New Hampshire. It is the highest peak in the Northeastern United States at and the most topographically prominent mountain east of the Mississippi River. The mountain is notorio ...
. Its highest elevation is . Active during the
Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...
epoch, the Sand Mountain Field began erupting about 4,000 years ago. The field includes 23
basalt Basalt (; ) is an aphanite, 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 planetary surface, surface of a terrestrial ...
ic and basaltic andesitic
cinder cone A cinder cone or scoria cone is a steep, volcanic cone, conical landform of loose pyroclastic rock, pyroclastic fragments, such as volcanic ash, clinkers, or scoria that has been built around a volcanic vent. The pyroclastic fragments are forme ...
s and
lava flows 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 unde ...
, for a total of 42 volcanic vents within two roughly north–south trending alignments. Its total
dense-rock equivalent Dense-rock equivalent (DRE) is a volcanologic calculation used to estimate volcanic eruption volume. One of the widely accepted measures of the size of a historic or prehistoric eruption is the volume of magma ejected as pumice and volcanic ash, k ...
eruptive output is , with subfeatures including a
tephra Tephra is fragmental material produced by a Volcano, volcanic eruption regardless of composition, fragment size, or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, ...
field and a
lava tube A lava tube, more rarely called a pyroduct, is a 'roofed conduit through which molten lava travels away from its vent'. If lava in the tube drains out, it will leave an empty cave. Lava tubes are common in low-viscosity volcanic systems. La ...
system. Future activity is possible, but according to the
Volcano Hazards Program The Volcano Hazards Program is a program directed by the USGS that monitors the activity of volcanoes and the public awareness of eruptions. Under the mandate of the Robert T. Stafford Disaster Relief and Emergency Assistance Act (Stafford Act), the ...
of the
United States Geological Survey The United States Geological Survey (USGS), founded as the Geological Survey, is an agency of the U.S. Department of the Interior whose work spans the disciplines of biology, geography, geology, and hydrology. The agency was founded on Mar ...
, the threat from the field itself is low. The field lies within the
Willamette National Forest The Willamette National Forest is a United States National Forest, National Forest located in the central portion of the Cascade Range of the U.S. state of Oregon. It comprises . Over 380,000 acres (694 mi2, 1,540 km2) are National Wil ...
near
Santiam Pass Santiam Pass is a mountain pass in the Cascade Range in central Oregon in the United States. It is located on the border between Linn and Jefferson counties, about northwest of Sisters, between the prominent volcanic horns of Three Fingered ...
. It supports some forested areas, which grow well on lava flows with tephra that serves as suitable soil for stands of
Douglas fir The Douglas fir (''Pseudotsuga menziesii'') is an evergreen conifer species in the pine family, Pinaceae. It is the tallest tree in the Pinaceae family. It is native to western North America and is also known as Douglas-fir, Douglas spruce, Or ...
and
western hemlock ''Tsuga heterophylla'', the western hemlock or western hemlock-spruce, is a species of hemlock native to the northwest coast of North America, with its northwestern limit on the Kenai Peninsula, Alaska, and its southeastern limit in northern ...
and less commonly
western red cedar ''Thuja plicata'' is a large evergreen coniferous tree in the family Cupressaceae, native to the Pacific Northwest of North America. Its common name is western redcedar in the U.S. or western red cedar in the UK, and it is also called pacific re ...
. The surroundings represent an area of geological interest, and
scoria Scoria or cinder is a pyroclastic, highly vesicular, dark-colored volcanic rock formed by ejection from a volcano as a molten blob and cooled in the air to form discrete grains called clasts.Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackso ...
has been quarried from one of the field's volcanic cones for highway supplies. Nearby tourist destinations include a
ski resort A ski resort is a resort developed for skiing, snowboarding, and other winter sports. In Europe, most ski resorts are towns or villages in or adjacent to a ski area–a mountainous area with pistes (ski trails) and a ski lift system. In North Am ...
, Tamolitch Falls, and Clear Lake.


Geography

The Sand Mountain Field is part of the
Cascade volcanic arc The Cascade Volcanoes (also known as the Cascade Volcanic Arc or the Cascade Arc) are a number of volcanoes in a continental volcanic arc in western North America, extending from southwestern British Columbia through Washington and Oregon to No ...
and is located at the western edge of the High Cascades segment of the central Oregon Cascades, near the upper McKenzie River watershed in
Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...
, in the
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
. It encompasses an area of and has a maximum elevation of . Located within the
Willamette National Forest The Willamette National Forest is a United States National Forest, National Forest located in the central portion of the Cascade Range of the U.S. state of Oregon. It comprises . Over 380,000 acres (694 mi2, 1,540 km2) are National Wil ...
in the McKenzie Ranger District near
Santiam Pass Santiam Pass is a mountain pass in the Cascade Range in central Oregon in the United States. It is located on the border between Linn and Jefferson counties, about northwest of Sisters, between the prominent volcanic horns of Three Fingered ...
, the Sand Mountain Volcanic Field is southwest of Mount Jefferson and northwest of
Belknap Crater 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 ...
and
Mount Washington Mount Washington is an ultra-prominent mountain in the state of New Hampshire. It is the highest peak in the Northeastern United States at and the most topographically prominent mountain east of the Mississippi River. The mountain is notorio ...
. The field borders Clear Lake, the source for the McKenzie River, and lava flows from the field formed a dam that created the lake. Clear Lake encompasses near
Oregon Route 126 Oregon OR 126 (OR 126) is a state highway that connects coastal, western, and central parts of the U.S. state of Oregon. A short freeway section of OR 126 in Eugene and Springfield is concurrent with Interstate 105 (I-105). Rou ...
, with a shallow northern region and a deeper southern zone, which reaches a maximum depth of . Other nearby lakes include Lost Lake, Lava Lake, and Fish Lake. Fish Lake is an
ephemeral lake A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from t ...
that dries up during the summer season, formed by the
dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aqua ...
ming of local water drainages by a lava flow from Sand Mountain Volcanic Field about 3,850 years ago. Local topography has influenced eruptive activity in the past, directing lava flows downhill to the west and, with wind, directing
tephra Tephra is fragmental material produced by a Volcano, volcanic eruption regardless of composition, fragment size, or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, ...
to the northeast. Annual precipitation in the Oregon Cascades averages , with about 80 percent 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.


Ecology

The southern part of the field supports mature forests, but other zones with younger lava deposits are barren. Mature forests correspond to lava flow areas with tephra; areas that do not have tephra cover lack soil and support only limited vegetation. Below elevations of , these forests are typical of the
lowland Upland and lowland are conditional descriptions of a plain based on elevation above sea level. In studies of the ecology of freshwater rivers, habitats are classified as upland or lowland. Definitions Upland and lowland are portions of a ...
temperate climate In geography, the temperate climates of Earth occur in the middle latitudes (approximately 23.5° to 66.5° N/S of the Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ra ...
of the
Pacific Northwest The Pacific Northwest (PNW; ) is a geographic region in Western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Though no official boundary exists, the most common ...
, with
Douglas fir The Douglas fir (''Pseudotsuga menziesii'') is an evergreen conifer species in the pine family, Pinaceae. It is the tallest tree in the Pinaceae family. It is native to western North America and is also known as Douglas-fir, Douglas spruce, Or ...
and
western hemlock ''Tsuga heterophylla'', the western hemlock or western hemlock-spruce, is a species of hemlock native to the northwest coast of North America, with its northwestern limit on the Kenai Peninsula, Alaska, and its southeastern limit in northern ...
predominating. Notably, forests in the Sand Mountain volcanic field have fewer
western red cedar ''Thuja plicata'' is a large evergreen coniferous tree in the family Cupressaceae, native to the Pacific Northwest of North America. Its common name is western redcedar in the U.S. or western red cedar in the UK, and it is also called pacific re ...
trees than is common among other forests in the Pacific Northwest region.
Fen A fen is a type of peat-accumulating wetland fed by mineral-rich ground or surface water. It is one of the main types of wetland along with marshes, swamps, and bogs. Bogs and fens, both peat-forming ecosystems, are also known as mires ...
wetlands surround Lost Lake, which is about north–northeast of the field. Within Clear Lake is a
submerged forest A submerged forest is the ''in situ'' remains of trees, especially tree stumps, that lie submerged beneath a bay, sea, ocean, lake, or other body of water. These remains have usually been buried in mud, peat, or sand for several thousand years b ...
of Douglas fir trees. Well-preserved under of water, they can be seen standing on the bottom of the lake. The cold water prevents most life from growing, giving the lake its name, 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. The eruption altered the ecosystem and created new habitats in the lake, on its shores, and on the new lava flow deposits. Today, life in the lake includes naturally reproducing fish species in Clear Lake such as
brook Brook may refer to: Computing *Brook, a programming language for GPU programming based on C *Brook+, an explicit data-parallel C compiler *BrookGPU, a framework for GPGPU programming People * Brook (surname) *People with the given name Brook, ...
and
cutthroat trout The cutthroat trout (''Oncorhynchus clarkii'' clade) is a clade of four fish species of the Family (biology), family Salmonidae native to cold-water Tributary, tributaries of the Pacific Ocean, Rocky Mountains, and Great Basin in North America. ...
, and the water is restocked annually with
rainbow trout The rainbow trout (''Oncorhynchus mykiss'') is a species of trout native to cold-water tributary, tributaries of the Pacific Ocean in North America and Asia. The steelhead (sometimes called steelhead trout) is an Fish migration#Classification, ...
.


Geology

The
Cascade Range The Cascade Range or Cascades is a major mountain range of western North America, extending from southern British Columbia through Washington (state), Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as m ...
and
Cascade Volcanic Arc The Cascade Volcanoes (also known as the Cascade Volcanic Arc or the Cascade Arc) are a number of volcanoes in a continental volcanic arc in western North America, extending from southwestern British Columbia through Washington and Oregon to No ...
result from the
subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...
of the Juan de Fuca tectonic plate under the North American tectonic plate. 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 Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...
, volcanism has moved east in the central Oregon Cascades and moved west in the northern Cascades. The
graben In geology, a graben () is a depression (geology), depressed block of the Crust (geology), crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German language, German, meaning 'ditch' or 't ...
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 and a depth of . Predominantly, it has generated
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 include ...
(rich in
magnesium Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...
and
iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
) lava, producing about of magma within the past 15,000 years. Moreover, many of the identified eruptive vents from the
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), as well as the current and most recent of the twelve periods of the ...
include
scoria Scoria or cinder is a pyroclastic, highly vesicular, dark-colored volcanic rock formed by ejection from a volcano as a molten blob and cooled in the air to form discrete grains called clasts.Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackso ...
cones In geometry, a cone is a three-dimensional figure that tapers smoothly from a flat base (typically a circle) to a point not contained in the base, called the ''apex'' or '' vertex''. A cone is formed by a set of line segments, half-lines, ...
or other mafic vents. The High Cascades graben displays a unique geochemical signature with low- K tholeiite magma and a relatively enriched mantle source, produced by
extension Extension, extend or extended may refer to: Mathematics Logic or set theory * Axiom of extensionality * Extensible cardinal * Extension (model theory) * Extension (proof theory) * Extension (predicate logic), the set of tuples of values that ...
and
heat flux In physics and engineering, heat flux or thermal flux, sometimes also referred to as heat flux density, heat-flow density or heat-flow rate intensity, is a flow of energy per unit area per unit time (physics), time. Its SI units are watts per sq ...
. The Sand Mountain Volcanic Field was formed after magma entered rock that was fractured by faulting related to
subsidence Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope mov ...
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
basalt Basalt (; ) is an aphanite, 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 planetary surface, surface of a terrestrial ...
ic, though this was replaced several hundred years later by more
evolved Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...
,
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 Ameri ...
magma. Eruptions at Sand Mountain Field were fed by two or three
magma chamber A magma chamber is a large pool of liquid rock beneath the surface of the Earth. The molten rock, or magma, in such a chamber is less dense than the surrounding country rock, which produces buoyant forces on the magma that tend to drive it u ...
s, including a number of mafic magma sources over a brief span of distance and time. The Sand Mountain Volcanic Field includes 23 basalt and basaltic andesite
cinder cone A cinder cone or scoria cone is a steep, volcanic cone, conical landform of loose pyroclastic rock, pyroclastic fragments, such as volcanic ash, clinkers, or scoria that has been built around a volcanic vent. The pyroclastic fragments are forme ...
s and associated
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 Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...
s, which were produced by two roughly north–south trending alignments of 42 volcanic vents. The two groups cross near the Sand Mountain cinder cone; their alignments imply the existence of complex volcanic dikes under the field. Sand Mountain marks the largest cinder cone in the field, at a height of . According to the
Global Volcanism Program The Smithsonian Institution's Global Volcanism Program (GVP) documents Earth's volcanoes and their eruptive history during the Quaternary Period of Earth's geologic history, with particular emphasis on volcanic activity during the Holocene Epoc ...
, the field includes six major clusters of volcanic vents, all
pyroclastic Pyroclast, Pyroclastic or Pyroclastics may refer to: Geology * Pyroclast, or airborne volcanic tephra fragments * Pyroclastic rock, rock fragments produced and ejected by explosive volcanic eruptions * Pyroclastic cone, landform of ejecta fro ...
cones. These are the Central Group, Little Nash Crater, Lost Lake Group, Nash Crater, Sand Mountain Cones, and South Group. Slight variations in vent alignment within groups likely reflect the small differences in local tectonic stress fields. 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. There are three major geochemical groups in the field: Sand, Lost Lake, and Nash. Together they amount to , 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 , while the Nash and Lost Lake group both consist of four units. The has no associated lava deposits, and the has no associated volcanic vent. These two deposits exhibit unique compositions; SnoPark lava has relatively higher levels of
barium Barium is a chemical element; it has symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element. Th ...
and
potassium oxide Potassium oxide ( K O) is an ionic compound of potassium and oxygen. It is a base. This pale yellow solid is the simplest oxide of potassium. It is a highly reactive compound that is rarely encountered. Some industrial materials, such as fertil ...
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 Strontium is a chemical element; it has symbol Sr and atomic number 38. An alkaline earth metal, it is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is exposed to ...
), at 1081 ppm and 1343 ppm, respectively. Single lava units at the field have uniform compositions, which is distinct from other young lava deposits within the surrounding region; major distinguishing elements include
silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundan ...
(silica),
titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound derived from titanium with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or Colour Index Internationa ...
,
magnesium oxide Magnesium oxide (MgO), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2− ions ...
, and
calcium oxide Calcium oxide (formula: Ca O), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term '' lime'' connotes calcium-containing ...
. The Sand group has high compositional variation, ranging from basalt to basaltic andesite, while the Lost Lake group is mostly basalt, and the Nash group is completely composed of basaltic andesite. The Nash group shows distinctively high silica content and a unique ratio of
iron(II) oxide Iron(II) oxide or ferrous oxide is the inorganic compound with the formula FeO. Its mineral form is known as wüstite. One of several iron oxides, it is a black-colored powder that is sometimes confused with rust, the latter of which consists ...
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. According to Wood and Kienle (1993), the field has a lava composition of subalkaline basalt and basaltic andesite. Deligne et al (2016) argue that the field also has
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 ...
basalt. Morphologically, Sand Mountain Field lavas have blocky appearances, reaching thicknesses up to though certain parts of the Lost Lake group have a ropy,
pāhoehoe 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 unde ...
surface.


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 A forearc is a region in a subduction zone between an oceanic trench and the associated volcanic arc. Forearc regions are present along convergent margins and eponymously form 'in front of' the volcanic arcs that are characteristic of convergen ...
of the Cascades and the Central Cascades, so this unique magma may be the result of old, metasomatized material from the Earth's mantle. The basaltic andesite at Little Nash Crater includes many small
plagioclase Plagioclase ( ) is a series of Silicate minerals#Tectosilicates, tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continu ...
phenocryst image:montblanc granite phenocrysts.JPG, 300px, Granites often have large feldspar, feldspathic phenocrysts. This granite, from the Switzerland, Swiss side of the Mont Blanc massif, has large white phenocrysts of plagioclase (that have trapezoid sh ...
s with less abundant
olivine The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...
phenocrysts, with silica levels of about 56.8 percent. These flows are younger than 2,590 ± 150 years by radiocarbon dating. Basaltic lava from the Lost Lake cone group contained 2–3 percent olivine phenocrysts, which are slightly
porphyritic Porphyritic is an adjective used in geology to describe igneous rocks with a distinct difference in the size of mineral crystals, with the larger crystals known as phenocrysts. Both extrusive and intrusive rocks can be porphyritic, meaning ...
; these deposits have been radiocarbon dated to 1,950 ± 150 years BP. At Nash Crater, there are basaltic andesite lava flows with sparse olivine phenocrysts and silica levels of about 53.5 percent. The lava from the main Sand Mountain chain varies from 51.6–53.2 percent 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. The field also includes an extensive tephra deposit, which encompasses an area of and has a volume of . 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. Additionally, the tephra exhibits uniformity with a fine mode grain size of to and a lack of
lapilli Lapilli (: lapillus) is a size classification of tephra, which is material that falls out of the air during a volcanic eruption or during some meteorite impacts. ''Lapilli'' is Latin for "little stones". By definition lapilli range from in dia ...
. These tephra deposits vary in age from 3,440 ± 250 to 1,600 years BP, according to
radiocarbon dating Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for Chronological dating, determining the age of an object containing organic material by using the properties of carbon-14, radiocarbon, a radioactive Isotop ...
. They reach thicknesses of greater than as far as from the Sand Mountain cinder cone and greater than up to from the cinder cone. Microfractures within Sand Mountain clastic rock along with the blocky, equant shapes and density of
sideromelane Sideromelane is a vitreous basaltic volcanic glass, usually occurring in palagonite tuff, for which it is characteristic. It is a less common form of tachylite, with which it usually occurs together; however it lacks the iron oxide crystals di ...
and
tachylite Tachylite ( ; also spelled tachylyte) is a form of basaltic volcanic glass. This glass is formed naturally by the rapid cooling of molten basalt. It is a type of mafic igneous rock that is decomposable by acids and readily fusible. The color i ...
clastic rock in the field suggest that Sand Mountain Field lava interacted with water. According to McKay (2012), this likely came from groundwater. There is a
lava tube A lava tube, more rarely called a pyroduct, is a 'roofed conduit through which molten lava travels away from its vent'. If lava in the tube drains out, it will leave an empty cave. Lava tubes are common in low-viscosity volcanic systems. La ...
called Lucy's Cavern that funneled the Sand Mountain Volcanic Field flows. It has a length of at least and reaches depths of . Its roof has a
vaulted In architecture, a vault (French ''voûte'', from Italian ''volta'') is a self-supporting arched form, usually of stone or brick, serving to cover a space with a ceiling or roof. As in building an arch, a temporary support is needed while ring ...
appearance with drip-like features. There are also two circular "vertical pits" that reach depths of and , respectively. These open vertical conduit
lava cave A lava cave is any cave formed in volcanic rock, though it typically means caves formed by volcanic processes, which are more properly termed volcanic caves. Sea caves, and other sorts of erosional and crevice caves, may be formed in volcanic rock ...
s, 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 in diameter. Both Moss Pit and Century Pit have vertical, circular entrances with smooth, remelted lining. Moss Pit has a diameter of at the entrance, with a depth of . It also features a small chamber near its base, which slopes down for another . Century Pit lies to the east of Moss Pit, with an entrance in diameter. Surrounded by a wall of spatter material ranging from in height, it has a vertical drop of , its lower half widening to a chamber with dimensions of at its base. The western margin of the base has an opening about deep, and at that depth it is blocked by debris. The lower chambers for both pits may be influenced by a
fissure A fissure is a long, narrow crack opening along the surface of Earth. The term is derived from the Latin word , which means 'cleft' or 'crack'. Fissures emerge in Earth's crust, on ice sheets and glaciers, and on volcanoes. Ground fissure A ...
or may form part of an open
fissure vent A fissure vent, also known as a volcanic fissure, eruption fissure or simply a fissure, is a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is often a few metres wide and may be many kilo ...
.


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. 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.


Eruptive history

During the Holocene epoch, volcanic activity has been particularly concentrated between the North Sister volcano and
Three Fingered Jack 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 ot ...
, with at least 125 distinct eruptive centers active since the retreat of Pleistocene glaciers. Eruptive activity in the upper McKenzie River catchment has been taking place since after the eruption of
Mount Mazama Mount Mazama ( Klamath: ''Tum-sum-ne'') is a complex volcano in the western U.S. state of Oregon, in a segment of the Cascade Volcanic Arc and Cascade Range. The volcano is in Klamath County, in the southern Cascades, north of the Oregon– ...
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. 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. Before that, about 3,000 to 4,000 years ago, lava flows erupted from vents along the chain. They moved west and blocked
drainage Drainage is the natural or artificial removal of a surface's water and sub-surface water from an area with excess water. The internal drainage of most agricultural soils can prevent severe waterlogging (anaerobic conditions that harm root gro ...
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 and the Koosah Falls, as well as the long Clear Lake, which still contains branches and bark from tree debris after the eruption. The overall
dense-rock equivalent Dense-rock equivalent (DRE) is a volcanologic calculation used to estimate volcanic eruption volume. One of the widely accepted measures of the size of a historic or prehistoric eruption is the volume of magma ejected as pumice and volcanic ash, k ...
(DRE) volume for the volcanic field lavas and volcanic cones is estimated to be . The Sand group has a DRE volume of , Lost Lake a DRE volume of , and Nash group a DRE volume of . Past
radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to Chronological dating, date materials such as Rock (geology), rocks or carbon, in which trace radioactive impurity, impurities were selectively incorporat ...
gave Sand Mountain Volcanic Field's age within a 1,000 year range. More precise
paleomagnetic dating Geochronology is the science of determining the age of rocks, fossils, and sediments using signatures inherent in the rocks themselves. Absolute geochronology can be accomplished through radioactive isotopes, whereas relative geochronology is p ...
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. Deligne et al. (2016) agree with this age estimate, arguing that
tephrochronology 250px, Tephra horizons in south-central Iceland. The thick and light coloured layer at the height of the volcanologist's hands is rhyolitic tephra from Hekla. Tephrochronology is a Geochronology, geochronological technique for dating archaeolo ...
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. According to the Global Volcanism Program, a confirmed eruption dated to 950
BCE Common Era (CE) and Before the Common Era (BCE) are year notations for the Gregorian calendar (and its predecessor, the Julian calendar), the world's most widely used calendar era. Common Era and Before the Common Era are alternatives to the o ...
± 200 years had a
Volcanic Explosivity Index The volcanic explosivity index (VEI) is a scale used to measure the size of explosive volcanic eruptions. It was devised by Christopher G. Newhall of the United States Geological Survey and Stephen Self in 1982. Volume of products, eruption c ...
of 4, while another confirmed eruption at Jack Mountain dated to 5050 BCE had a Volcanic Explosivity Index of 2. While geological evidence suggests that eruptions at Sand Mountain Field were explosive, they differed from violent,
Strombolian eruption In volcanology, a Strombolian eruption is a type of volcanic eruption with relatively mild blasts, typically having a Volcanic Explosivity Index of 1 or 2. Strombolian eruptions consist of ejection of incandescent Scoria, cinders, lapilli, and vo ...
s because their very explosive eruptions were sustained over a long period of time, likely partly attributable to interaction with water. Walsh (2012) classifies the eruptions as
sub-Plinian Plinian eruptions or Vesuvian eruptions are volcanic eruptions characterized by their similarity to the eruption of Mount Vesuvius in 79 AD, which destroyed the ancient Roman cities of Herculaneum and Pompeii. The eruption was described in a le ...
. 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. 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 Conifers () are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a sin ...
branch found in Sand Mountain volcanic ash yielded an age of 3,440 ± 250 years
Before Present Before Present (BP) or "years before present (YBP)" is a time scale used mainly in archaeology, geology, and other scientific disciplines to specify when events occurred relative to the origin of practical radiocarbon dating in the 1950s. Because ...
(BP). Radiocarbon dating of charcoal on a lateral
moraine A moraine is any accumulation of unconsolidated debris (regolith and Rock (geology), rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a gla ...
near Nash Crater gave an age of 2,590 ± 150 BP. 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.


Future threats

The Sand Mountain Field is located from a population of roughly 500,000 people. It is close to a major transportation corridor from central Oregon to the
Willamette Valley The Willamette Valley ( ) is a 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 east, the ...
as well as a popular ski area, and future eruptions could have "substantial societal consequences" according to Deligne et al. (2016). 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. Tephra from eruptions at Sand Mountain could reach more than from the vent, and if lava flows reached forested regions they could initiate forest fires. However, according to the
Volcano Hazards Program The Volcano Hazards Program is a program directed by the USGS that monitors the activity of volcanoes and the public awareness of eruptions. Under the mandate of the Robert T. Stafford Disaster Relief and Emergency Assistance Act (Stafford Act), the ...
of the
United States Geological Survey The United States Geological Survey (USGS), founded as the Geological Survey, is an agency of the U.S. Department of the Interior whose work spans the disciplines of biology, geography, geology, and hydrology. The agency was founded on Mar ...
, the threat potential from the field is "Low/Very Low." 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. Moreover, hazardous volcanic gases could accumulate after an eruption, such as
sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a colorless gas with a pungent smell that is responsible for the odor of burnt matches. It is r ...
,
hydrogen chloride The Chemical compound, compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hyd ...
, and
hydrogen fluoride Hydrogen fluoride (fluorane) is an Inorganic chemistry, inorganic compound with chemical formula . It is a very poisonous, colorless gas or liquid that dissolves in water to yield hydrofluoric acid. It is the principal industrial source of fluori ...
.


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. In 1957, H. Williams produced a reconnaissance geological map, which was followed by further mapping by E. M. Taylor in 1965. Taylor's work determined the presence of 9 lava units at Sand Mountain Volcanic Field and another lava unit from Belknap Crater. A map published by Sherrod et al. (2004) built upon Taylor's studies. In November 1963, the
United States Forest Service The United States Forest Service (USFS) is an agency within the United States Department of Agriculture, U.S. Department of Agriculture. It administers the nation's 154 United States National Forest, national forests and 20 United States Natio ...
sent divers from the Whitewater Diver group from
Eugene Eugene may refer to: People and fictional characters * Eugene (given name), including a list of people and fictional characters with the given name * Gene Eugene, stage name of Canadian born actor, record producer, engineer, composer and musi ...
to obtain tree samples from Clear Lake using Aqua-Lung technology. Two samples were acquired from one tree section, both about in diameter, at a depth of about . Radiocarbon dating analysis suggested that the samples were dated to 3,200 ± 220 and 2,705 ± 200 years Before Present, respectively; radiocarbon dating performed by Licciardi et al. (1999) found a similar result of 2750 ± 45 years Before Present. 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. Red and oxidized scoria has been
quarried A quarry is a type of open-pit mining, open-pit mine in which dimension stone, rock (geology), rock, construction aggregate, riprap, sand, gravel, or slate is excavated from the ground. The operation of quarries is regulated in some juri ...
from Little Nash Crater for highway supplies near Santiam Pass. The Carmen Smith Hydroelectric Power Scheme is fed by the upper McKenzie River and generates about of electricity.


Recreation

The upper McKenzie River catchment area includes Clear Lake and Tamolitch Pool, which represent popular tourist locations. At Clear Lake, popular activities include
canoeing Canoeing is an activity which involves paddling a canoe with a single-bladed paddle. In some parts of Europe, canoeing refers to both canoeing and kayaking, with a canoe being called an 'open canoe' or Canadian. A few of the recreational ...
, 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. Volcanic formations including lava flows within McKenzie Pass have historically attracted the attention of passing motorists. There is also a
ski resort A ski resort is a resort developed for skiing, snowboarding, and other winter sports. In Europe, most ski resorts are towns or villages in or adjacent to a ski area–a mountainous area with pistes (ski trails) and a ski lift system. In North Am ...
at Santiam Pass.


See also

*
List of volcanic fields A list of volcanic fields follows below. {{Incomplete list, date=May 2025 Africa Algeria * Atakor volcanic field * In Teria volcanic field * Manzaz volcanic field * Nemours-Nedroma * Tafna Beni Saf * Tahalra volcanic field Cameroon * Oku Volcan ...


References


Sources

* * * * * * * * . * * * . * * * {{refend Cascade Volcanoes Lava fields Volcanic fields of Oregon Volcanoes of Oregon