Shield volcano in Oregon, United States
Newberry Volcano is a large, active, shield-shaped stratovolcano located about south of Bend, Oregon, United States, east of the major crest of the Cascade Range, within the Newberry National Volcanic Monument. Its highest point is Paulina Peak. Newberry is the largest volcano in the Cascade Volcanic Arc, with an area of when its lava flows are taken into account. From north to south, the volcano has a length of , with a width of and a total volume of approximately . It was named for the geologist and surgeon John Strong Newberry, who explored central Oregon for the Pacific Railroad Surveys in 1855.
The volcano contains a large caldera, in diameter, known as the Newberry Caldera. Within the caldera are two lakes: Paulina Lake and East Lake. The volcano and its vicinity include many pyroclastic cones, lava flows and lava domes; Newberry has more than 400 vents, the most of any volcano in the contiguous United States. Glaciers may have once been present at the volcano, though this remains contested. The area has a dry climate with low precipitation levels and little surface runoff.
The origin of the volcano remains somewhat unclear; while some scientists believe it originated from an independent hotspot, most evidence indicates that it formed from the subduction of the oceanic Juan de Fuca and Gorda tectonic plates under the continental North American Plate. Eruptive activity at Newberry Volcano began about 600,000 years ago and has continued into the Holocene, the last eruption taking place 1,300 years ago. Unlike other shield-shaped volcanoes, which often erupt basaltic lavas only, Newberry Volcano has also erupted andesitic and rhyolitic lavas. A popular destination for hiking, fishing, boating, and other recreational activities, the volcano lies within of 16,400 people and within of nearly 200,000 people, and it continues to pose a threat to life. Still considered an active volcano, it could erupt and produce lava flows, pyroclastic flows, lahars (volcanically induced mudslides, landslides, and debris flows), ashfall, earthquakes, avalanches, and floods. To track this threat, the volcano and its surroundings are closely monitored with sensors by the United States Geological Survey.
Geography.
The center of Newberry Volcano lies to the south of the city of Bend, at the intersection of Deschutes, Klamath and Lake counties in Oregon, where it is one of the most accessible volcanoes in the state. It is the largest volcano in the Cascade Volcanic Arc at , and has roughly the same area as the state of Rhode Island at if its lava flows are included. Newberry lies east of the major crest of the Cascade Range in the High Lava Plains region, rising above its surroundings. From north to south, the volcano runs for a length of , with a width of and a total volume of about . Because of its enormous size and topographic prominence, it is often confused for an entire mountain range.
Newberry Volcano has a somewhat dry climate due to its location in the rain shadow of the Cascade Range. Climate data for the Newberry National Volcanic Monument are collected at the Lava Butte cinder cone, which had an average annual precipitation of from 2002 to 2012. Summer temperatures average from , dipping to average minimum and maximum temperatures of during the winter season. Spring has average temperatures of , while fall temperatures average . Each year, total precipitation consisting of winter snow and summer rain varies from in the highest parts of the region, and surface runoff rarely occurs even during heavy rain showers. Only one stream appears on Newberry's entire surface, and it remains unclear whether the volcano has ever been able to support glaciers on its slopes, since the mountain lacks cirques (amphitheater-like valleys formed by glacial erosion) or evidence of contact between lava and ice. However, displaced glacial erratics have been found far from their native areas, moraine sediment has been deposited on the eastern and northeastern slopes of the volcano, and the mountain's various cone features have "boat" shapes that indicate glacial alteration. The precise history of glaciers on the volcano is debated, but dry channels and dry waterfalls on the eastern and western slopes are evidence that the volcano once held water.
The volcano has two crater lakes, Paulina Lake and East Lake, which are filled by precipitation and percolation of ground water. Paulina Lake occupies an area of and reaches a maximum depth of , and it is separated from East Lake by a narrow isthmus, which is composed of rhyolite lava. East Lake has a smaller area of with a maximum depth of . The lakes have historically flooded channels surrounding the volcano. A large flood between 4,000 and 2,300 years ago released up to 12,000 acre feet (0.0148 km3) in volume from Paulina Lake, filling the valley floor above the Paulina Prairie, which surrounds the lake. It was possibly caused by the failure of a rock ledge in height, rather than eruptive activity. Another flood took place in 1909 on the Deschutes River downstream from where it meets its tributary the Little Deschutes River.
Ecology.
The Newberry National Volcanic Monument forms part of the northern section of the Mazama Ecological Province, which has soil comprised by aeolian pumice and volcanic products over basalt bedrock. Flora within the Newberry Volcano area includes forests of juniper, whitebark pine, ponderosa pine (including Oregon's largest ponderosa pine tree), lodgepole pine, jack pine, and white fir, in addition to other plants like Indian paintbrush, purple penstemon, bitterbrush, manzanita, and snowbrush. Infestations by mountain pine beetles have killed many lodgepole pines in the area. Animals near Newberry Volcano include burrowing owls, kangaroo rats, lizards, bats, rattlesnakes, eagles, porcupines, otters, bobcats, mule deer, Roosevelt elk, ducks, and American pika.
Lava flows from Newberry display varied vegetation cover, and there are variable levels of flora between flows, though the level of vegetation and species diversity generally increase with elevation. Dominant plant species on lava flows include oceanspray and wax currant, with rabbitbrush also common. Though forbs are not widespread on the lava flows, where they do occur Davidson's penstemon and hotrock penstemon dominate. Above elevations of , roundleaf alumroot is common, particularly near the edges of lava flows. All lava flows support patches of grasses such as Idaho fescue, especially on north-facing slopes. One lava flow at Lava Butte is barren except for scattered, dense patches of greenleaf manzanita.
The Lava Cast Forest is a group of trees molded by lava from an eruption 6,000 years ago. Today, the surrounding site lies within the Newberry National Volcanic Monument and includes 11 kīpukas, plots of land surrounded by one or more younger lava flows. These habitat islands range from in area and sustain forests that have not been significantly altered by humans other than nearby fire suppression and land management efforts. Consisting of pure and mixed forest stands, these forests include ponderosa pine, lodgepole pine, and grand fir/white fir hybrid trees, which are supported by young soils derived from Mazama pumice.
Geology.
Overlapping with the northwestern corner of the Basin and Range Province, also known as the High Lava Plains, Newberry Volcano lies within a Cenozoic highland marked by normal faults known as the Brothers Fault Zone. It is situated at the intersection of the Brothers Fault Zone with the north–northwest-trending Sisters and northeast-trending Walker Rim fault zones. In the mantle under Newberry Volcano, P and S seismic waves exhibit an unusually low wave velocity. The Earth's crust thins from at the nearby Three Sisters volcano complex to near Newberry, where it has a high Poisson's ratio.
The oldest rocks in this region include silicic (rich in silica) lava domes from the late Miocene or early Pliocene, which lie near the province's eastern and southern borders, respectively. Volcanism in this area suggests a progression of silicic eruptions, known as the Newberry Trend, that moves in a northwest-trending direction from the Harney Basin to Newberry Volcano and the rest of the Cascade Range. Newberry Volcano's origins are somewhat controversial; some scientists think it originated from an independent hotspot, but overwhelming evidence suggests that it is part of the Cascades Arc and was produced by the subduction of the oceanic Juan de Fuca and Gorda tectonic plates under the continental North American Plate. However, Newberry Volcano has been transformed by tectonic processes, possibly related to subductive mechanisms that enhance melting of the Juan de Fuca tectonic plate. The High Lava Plains Trend, or the Newberry Trend, moves at an oblique angle to the underlying North American tectonic plate, for which subduction counterflow, gravitational flow along the lithosphere's base, faulting, and extension of the Basin and Range Province have all been proposed as possible mechanisms. At Newberry, the subducting plate has a depth that is shallower than elsewhere in the major crest of the Cascades,[b] accounting for its unique magmas. Newberry Volcano is likely fed by a magma chamber under the large, cauldron-like caldera at its summit. This caldera has dimensions of and formed about 75,000 years ago.
Newberry Volcano first formed about 600,000 years ago and has since been built up by several thousand eruptions. About 500,000 years ago, Mount Newberry attained an elevation of . The caldera-forming event occurred about 75,000 years ago from a major explosive eruption. It formed the crater lakes and Paulina Peak—which is the highest point on the volcano, at .[a]
As a result of its caldera-forming eruption, Newberry has a horizontal profile, which is typical of a shield volcano. However, it is also considered a composite volcano, made up of a matrix of lava flows and pyroclastic deposits. Unlike more typical composite volcanoes in the Cascades, it formed from several eruption types including more traditional explosive eruptions and more fluid effusive events; thus it is usually classified as a "shield-shaped composite volcano", or shield-shaped stratovolcano. The volcano has a caldera at its summit, which has a diameter of and features two crater lakes: Paulina Lake and East Lake. This caldera, known as the Newberry Crater, is forested, with small parts of its surface covered with lava flows and pumice deposits. Before the caldera's creation, the mountain's summit was greater in height than its current elevation. The caldera has reformed several times throughout the volcano's history, burying the caldera floor to a depth of and creating concentric calderas, each smaller than its predecessor. The first caldera—the volcano's largest caldera, forming approximately 300,000 years ago—was produced by the eruption of of pyroclastic ejecta, which created the Tepee Draw tuff and ash deposits that cover the volcano's eastern flank. The last crater formed after an explosive eruption about 80,000 years ago, which ejected up to of pyroclastic materials. Throughout this progression, the volcano shifted from rhyodacitic pumice to basaltic ash flows, the latter producing the Black Lapilli tuff that covers the western side of the volcano. Since the last caldera-forming eruption 80,000 years ago, the volcano has undergone silicic eruptions at the caldera and produced basaltic and basaltic andesite lava flows that extended down its outer flanks. The tephra and ash from the Black Lapilli tuff by the caldera formed agglutinates around its rim. Newberry Volcano is cut by several fault scarps, small step offsets on the ground surface where one side of a fault has moved vertically with respect to the other.
At the center of the isthmus that separates Newberry Volcano's two crater lakes is the central volcanic cone, named Central Pumice cone, which reaches above East Lake. With a broad, flat top, it formed during an explosive eruption about 7,000 years ago, and sits in the center of the caldera.
Compositionally, lava from the Newberry Volcano has varied from primitive basalts with high magnesium levels to more evolved tholeiitic and calc-alkaline deposits (based on the major element characteristics of the lavas). Primitive lavas exhibit high abundances of chromium and nickel as well as variable concentrations of fluid-mobile elements like barium and strontium. Tholeiitic and calc-alkaline lavas display overlap in magnesium, calcium oxide, and aluminum oxide levels but differ in that the tholeiites have lower contents of silica and potassium oxide and higher iron(II) oxide, titanium dioxide, and sodium oxide. There is also much overlap in isotopic composition, though the tholeiitic lavas mark the low point for 87Sr/86Sr and the high point for 143Nd/144Nd and 176Hf/177Hf. Examination of Newberry lavas with olivine-plagioclase hygrometry shows that tholeiites are anhydrous (less than 0.5 percentage by weight water) and thus distinct from