| Newberry Volcano - Paulina Peak | |
|---|---|
Newberry Caldera, with Paulina Lake, East Lake, and Big Obsidian Flow |
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| Elevation | 7,989 ft (2,435 m) NAVD 88[1] |
| Location | |
| Location | Deschutes County, Oregon, USA |
| Range | Cascade Range |
| Topo map | USGS Paulina Peak |
| Geology | |
| Type | Shield volcano with pyroclastic cones |
| Age of rock | About 600,000 years old [2] |
| Volcanic arc/belt | Cascade Volcanic Arc |
| Last eruption | 690 AD ± 100 years [3] |
| Climbing | |
| First ascent | 1873 |
| Easiest route | Road to Paulina Peak |
Newberry Volcano (with Newberry Caldera) is a large potentially active[2] shield volcano located 40 miles (64 km) east of the Cascade Range and about 20 miles (32 km) southeast of Bend, Oregon. It is not a typical shield volcano. In addition to erupting basaltic lavas, it also has erupted andesitic and even rhyolitic lava.
The volcano is 20 miles (32 km) in diameter and has an approximate volume of 80 cubic miles (330 km3). It possesses a large oval-shaped caldera 4 × 5 miles (6.4 × 8.0 km) in diameter, called the Newberry Caldera. Within the caldera there are two lakes (Paulina Lake and East Lake), many pyroclastic cones, lava flows, and obsidian domes.
A deep gash in the northern caldera wall, dubbed "The Fissure", is the end of a 29-mile (47 km) long series of fractures called the Northwest Rift Zone. Approximately 6,100 years ago, fissure basalt flows erupted from the rift and covered part of Newberry's northwest flank.
Newberry Volcano was named for John Strong Newberry, who explored central Oregon for the Pacific Railroad Surveys in 1855.[4]
During the Apollo program, parts of the volcano that resemble the Moon's surface were used to train the astronauts.
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The Newberry Volcano lies at the northwest end of both the Brothers Fault Zone, and the High Lava Plains (area of blue lines on diagram at right) of volcanic features in central Oregon that have been developing since about 16 Ma. Volcanism in the High Lava Plains is bimodal, having both basaltic (mafic) and rhyolitic (silicic) types of lava. Some of the rhyolites show a progression in ages from about 10 Ma in the east to the geologically recent Newberry Caldera in the west. This track, and its implication of a moving source, roughly mirrors the similar track of the Yellowstone Hotspot from the McDermitt Caldera on the Oregon—Nevada border, on which basis the Newberry volcanism has been attributed to a so-called hotspot (a plume of hot material arising from the earth's mantle). But whereas the Yellowstone Hotspot reflects the motion of the North American plate across a hotspot, the Newberry track does not. Although the cause of the intense regional volcanism around 16 Ma is hotly debated,[5] the age progression across the High Lava Plains is now attributed to a reservoir of hot material that expanded over time, and the linearity of the trend attributed to exploitation of a deep, pre-existing weakness in the crust associated with the Brothers Fault Zone.[6]
A great deal of volcanic activity has occurred on Newberry's shield, which itself has one of the largest collections of cinder cones, domes, lava flows, and fissures in the world—so much so that local residents call these parasitic vents the "Paulina Mountains", thinking of them as a separate mountain range. Most of the cinder cones are 200 to 400 feet (60 to 120 m) high and have shallow saucer-shaped summit craters. They are typically surrounded by basalt or andesite that erupted from their bases forming large lava beds. The northern flank holds three distinct lava tube systems that formed in pāhoehoe: the Horse Lava Tube System, Arnold Lava Tube System, and the Lava Top Butte basalt.[7] On the northwest flank of the volcano is Lava Butte, located next to Highway 97 south of Bend, is a good example of this kind of cinder cone and an ʻaʻā lava bed. There are also about 20 rhyolite domes or fissures on the eastern, southern, and western flanks. Larger examples include 580,000-year-old McKay Butte on the west flank, 80,000-year-old China Hat and 850,000-year-old East Butte on the far eastern base.
During the late Pleistocene and Holocene periods, there have been six eruptive episodes. Four of them rhyolitic, on the eastern half of the caldera, and two basaltic, on the flanks.
Newberry's highest point is located 1,500 feet (460 m) above the southern caldera floor on Paulina Peak, which is just one peak on the caldera rim. The volcano's south flank descends into the basaltic flatlands of central Oregon.
Newberry Caldera has existed possibly as long as 500,000 years, when the cone of the volcano is thought to have first collapsed. Subsequent caldera-forming collapse events have further deepened the caldera but volcanic material and lake-bed sediments have largely filled in much of this depth.
Within the caldera, there are two lakes (Paulina Lake and East Lake), many cinder cones, lava flows, and obsidian domes. The land area of the caldera is often heavily forested, except in areas where there are more recent volcanic flows and features. Paulina Lake is drained by Paulina Creek, which passes through a narrow gorge through the western part of the caldera rim. East Lake does not have a known outlet and is 40 feet (12 m) higher than Paulina Lake. 6700-year-old basalt flows separate the two caldera lakes. Rising 700 feet (210 m) above this flow is the Central Pumice Cone.
Both lakes have hot springs, and drilling in 1981 found that temperatures in the caldera reach 280 °C (540 °F) at 3,057 feet (932 m) below the caldera floor. This is the highest temperature ever recorded at a dormant Cascade volcano, hotter than even The Geysers of California, the world's largest producer of geothermal power.
Newberry has had a caldera for possibly as long as 500,000 years, when a large Plinian Eruption sent so much pyroclastic material gushing from its vent that the then-emptied magma chamber collapsed. This was repeated for several eruptions; each forming a slightly smaller caldera. The half-million-year-old (estimated) Teepee Draw tuff covers much of the volcano's shield and was from an eruption with an estimated volume of 10 cubic miles (42 km3). This is thought to be the first in a series of caldera-forming eruptions that issued from Newberry's main vent system. One of the later layers is cut by Newberry's only stream, Paulina Creek.
Subsidence of the caldera through time has been partly offset by the deposition of tephra, lava flows, and lake sediment. The USGS has drilled 3,057 feet (932 m) below the present surface of the caldera and has found that:
There are several large flows of obsidian in the caldera, one of which, Big Obsidian Flow, was created around 1400 years ago and is thus the most recent caldera eruption. This particular flow erupted from a vent or fissure near the southern wall of the caldera and partially engulfed the Lost Lake pumice ring.
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