| Goat Rocks | |
|---|---|
 The Goat Rocks, with Gilbert Peak at upper left | |
| Highest point | |
| Elevation | 8,201 ft (2,500 m)[1] |
| Coordinates | 46°29′19″N121°24′21″W / 46.48861°N 121.40583°W /46.48861; -121.40583 |
| Geography | |
 | |
| Location | Lewis /Yakima counties,Washington, U.S. |
| Parent range | Cascade Range |
| Topo map(s) | USGS Old Snowy Mountain, Walupt Lake |
| Geology | |
| Rock age | 3.2 million - ~500,000 years |
| Mountain type | Extinctstratovolcano |
| Volcanic arc | Cascade Volcanic Arc |
| Last eruption | ~500,000 years ago |
| Climbing | |
| First ascent | Fred G. Plummer, 1899 |
| Easiest route | Scrambling |
Goat Rocks is anextinctstratovolcano in theCascade Range, located betweenMount Rainier andMount Adams in southernWashington, in the United States. Part of theCascade Volcanoes, it was formed by thesubduction of theJuan de Fuca Plate under the western edge of theNorth American Plate. The volcano wasactive from 3.2 million years ago until eruptions ceased between 1 and 0.5 million years ago. Throughout its complex eruptive history, volcanism shifted fromsilicicexplosive eruptions to voluminous,mafic activity.
The volcano and the surroundingGoat Rocks Wilderness, established in 1964, are named after the numerousmountain goats which live in the area. The variable climate of the wilderness area supports a host of wildlife, including marmots, pikas, deer, and elk. Various peaks within the wilderness can be climbed orscrambled, and other activities such as hiking are permitted. The area is rife with minerals and resources, including coal,cobalt,copper, andbase metals.
Goats Rocks volcano is located in southernWashington, 113 km (70 mi) west ofYakima,[2] at latitude 46.50° N and longitude 121.45° W.[3] This region of the Cascades was originally occupied by Native Americans, who hunted and fished in its vicinity and used its trails as trade routes.[4] Goat Rocks lies in a zone of intermittent volcanism which has produced many small volcanic vents, also including theMount Adams volcanic field andIndian Heaven.[5] Situated in the eastern portion of theCascade Range, Goat Rocks lies at the northwest corner of theKlickitat River basin.[6] As a member of theCascade Volcanoes,[1] Goat Rocks was produced by thesubduction of the oceanicJuan de Fuca plate under the western edge of the continentalNorth American Plate. This fault, known as theCascadia subduction zone, lacks the deepoceanic trench usually found at convergent plate boundaries, which can probably be explained by its slow rate of subduction. According to theUnited States Geological Survey, the Nazca and North American plates converge at a rate of 3 to 4 cm (1 to 2 in) each year, just half of their convergence rate as recently as 7 million years ago.[7]
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The Cascade Volcanoes in Washington are restricted to four belts; Goat Rocks forms one segment of the north–south trending Mount Adams belt that also incorporates Tumac Mountain, Adams, and the King Mountain Fissure Zone. Of the four Cascade arcs, this belt contains the second most volcanoes, and its volcanoes are predominantly made ofcalc-alkalic totholeiitic to basaltic andesite lava.[8] Goat Rocks and its immediate vicinity are underlain by pre-Tertiarygreywacke andargillite, and these deposits are cut by several prominent northward-trendingfaults.[9] Overlaying these deposits areCenozoic volcanic rocks, including the thick,Eocene-agedOhanapecosh Formation, comprised by chemically alteredbasalt andandesite lava flows andbedded andesite anddacitevolcaniclastic rock. In turn, theStevens Ridge Formation overlies the Ohanapecosh layer, featuringquartz-bearingsilicictuff,rhyolite, and other volcaniclastic rocks.[10] Under both layers is theRussell Ranch Formation, 2,298 to 3,048 m (7,539 to 10,000 ft) in thickness, which contains deposits oflapilli and tuff hinting at acaldera, although geologists have failed to identify clear evidence for the formation of a caldera in this zone.[11]
Together with Mount Adams,Mount Rainier, andMount St. Helens, the Goat Rocks volcano is part of a triangle of volcanoes, an arrangement not found elsewhere in the Cascades. This may be related to a mid-crust zone with abnormally high electrical conductivity, the Southern Washington Cascades Conductor (SWCC), which is not well understood by geologists. Scientists from the United States Geodynamics Committee hypothesized in 1994 that this anomaly is associated with the thrust of a large deposit ofsedimentary rock against acontinental margin.[12] However, Hill et al. (2009) dismiss this view as it proves inconsistent with maps made frommagnetotelluric readings of the area. Instead, they propose that the anomaly is linked to the region's volcanism, which has causedpartial melting of the crust.[13]
The oldest Cascade stratovolcano formed after theColumbia River Basalt Group, Goat Rocks is roughly equal in volume to Mount St. Helens and smaller in volume than Mount Baker, at approximately 60 km3 (14 cu mi). Rough estimates place the composition of the volcano as 40%tuff andbreccia.[14] The remains of its lava flows can be found in the Tieton, Klickitat, and Cispus river valleys, their elevationreversed by erosion to make them resembleridges. These flows have been thoroughly eroded, but testify to the volcano's previous size.[15]
Although it may have once been a towering stratovolcano,[16] Goat Rocks has undergone extensiveerosion since its extinction.[17] Once eruptions ceased, the ongoing forces ofglacialerosion, as well ashydrothermal alteration of the volcano's interior, stripped away layers ofvolcanic ash deposits andlava flows,[1] uncovering the rockylava spines wheremagma had cooled and hardened within the conduits of the volcano.[18] Nearly all the remaining volcanic debris has been partially covered by a younger layer of rock.[14]
The Goat Rocks area is notable for its extensive glaciers, despite its modest elevation and southerly location relative to the rest of the Washington Cascades. Four major glaciers mantle the north and northeast slopes of the peaks:Conrad Glacier,[19]McCall Glacier,[20]Meade Glacier,[19] andPackwood Glacier,[21] along with numerous smaller permanent snowfields.[22]
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The elevation of the Goat Rocks volcano and its immediate vicinity varies from 914 to 2,500 m (2,999 to 8,202 ft) at its highest point,Gilbert Peak. Because of extensive glaciation and erosion, the peaks surrounding Goat Rocks are at most moderate in height.[1]
| Gilbert Peak (Mount Curtis Gilbert) | 2,500 m (8,202 ft)[1] |
| Old Snowy Mountain | 2,402 m (7,881 ft)[23] |
| Ives Peak | 2,414 m (7,920 ft)[24] |
| Tieton Peak | 2,369 m (7,772 ft)[25] |
| Johnson Peak | 2,282 m (7,487 ft)[26] |
| Bear Creek Mountain | 2,238 m (7,343 ft)[27] |
| Hogback Mountain | 2,071 m (6,795 ft)[28] |
Goat Rocks is astratovolcano with a somewhat complicated eruptive history. It first became active approximately 3.2 million years ago during thePliocene epoch, undergoingexplosive eruptions[18] that ejectedsilicic lava with highlyfelsic rocks likerhyolite. One of these events produced 650 m (2,133 ft) oftuff that remains, exposed, on the east flank of the existing mountain. This rhyolitic episode also produced the Devil's Horn caldera.[29] The amount of rhyolite tuff exceeds 20 km3 (4.8 cu mi).[30]
Three million years ago Goat Rocks shifted tomafic volcanism, eruptingolivine andbasalt. As eruptions continued into thePleistocene epoch, the lava flows became increasinglyandesitic, containing mostlypyroxene withphenocrysts as well ashornblende minerals. These andesitic flows formed the volcano's major edifice between roughly 2.5 and 0.5 million years ago,[3] which may have resembled contemporary Mount Rainier.[31] At this point in time, Goat Rocks's eruptions had very high volumes and extended far from the volcano,[3] possibly because multiple satellite vents contributed to eruptions.[9]
Approximately 1.64 million years ago, Goat Rocks generated an andesitic lava flow extending 80 km (50 mi) down theNaches andTieton Rivers, which has been recognized as the longest andesite flow on Earth having a total volume of 6.6 km3 (1.6 cu mi).[32][3] About 250,000 years after this andesite flow a second flow erupted from Bear Creek Mountain, the second flow took a similar path as the older one and had a total volume of 2.5 km3 (0.60 cu mi).[32] Many of the flows immediately surrounding the volcano have since been cut byintrusivedikes, which form a radial arrangement around the volcano's core.
As erosion occurred on a large scale, the volcano remained active, producing more hornblende andesite lava flows. Eruptive activity continued atOld Snowy Mountain into the middle to late Pleistocene, yielding hornblende andesite lava flows that were subsequently glaciated in theCispus River valley; whether Old Snowy Mountain is a vent of Goat Rocks or an independent volcano remains unclear.[2] Hornblende andesite can also be found on top of the highest point in Goat Rocks, Gilbert Peak.[2]
Hogback Mountain, ashield volcano north of Goat Rocks and south ofWhite Pass, was identified by Siebert et al. (2010) as a satellite vent of Goat Rocks.[33] Rising 700 m (2,297 ft) in elevation, it erupted more than 200 m (656 ft) of olivine basalt and basaltic andesite from the end of the Pliocene through the early Pleistocene.[2] Eruptions from Goat Rocks formed a spread-outvolcanic field populated by smalllava domes and cinder cones as far north as an unnamed vent on American Ridge north ofBumping Lake.Spiral Butte alongUS 12 near White Pass is one of these vents, having erupted less than 690,000 years ago.[34] The volcanic field's dimensions are approximately 29.9 by 15 km (19 by 9 mi).[15]
Goat Rocks is now classified as anextinct volcano, as its most recent eruptive activity was during the Pleistocene.[14] The last eruption from the Goat Rocks complex occurred around 115,000 years ago.[35] It was an effusive lava flow known as the Clear Fork Lava. The flow was primarily composed ofdacite and flowed 12 km (7.5 mi) along the White Pass Highway and has an estimated volume of 0.55 km3 (0.13 cu mi).[35]
Land surrounding Goat Rocks was first protected by theUnited States Department of Agriculture in February 1931, when approximately 18,009 hectares (44,501 acres) was set aside for preservation. In 1935, this was increased to 29,315 hectares (72,439 acres) of land, then to 33,459 hectares (82,679 acres) in 1940. In 1964, the United States Congress created the Goats Rock Wilderness as part of theNational Wilderness Preservation System, delegating its management to theUnited States Forest Service. Since additional land was incorporated in 1984,[36] it now encompasses 43,745 hectares (108,096 acres) between Mount Rainier and Mount Adams, straddling theGifford Pinchot andOkanogan-Wenatcheenational forests.[37] It is bordered by theYakama Indian Reservation to the southeast.[36]
The wilderness ranges from 914 to 2,500 m (2,999 to 8,202 ft) in elevation, featuringalpine tundras with glaciers, small lakes, and ponds, as well as 15 different routes that amount to 193 km (120 mi) of trails. One of these trails constitutes the highest segment of the famousPacific Crest Trail in Washington,[38] running for 50 km (31 mi) north–south through the middle of the wilderness area.[37] Because this route is located at such a high elevation, its hikers may experience violent storms that could be dangerous for unprepared parties.[39] Much of the wilderness is located above thetimberline, offering views of alpine scenery.[36]
Weather within the Wilderness varies due to the mountains acting as a barrier for both weather and temperature. The Cascade Range mountains prevent wet storms from moving, forcing air to rise and then cool. This cooling air cannot hold as much moisture, causing heavy precipitation (up to 381 cm (150 in) in rainfall annually) on the western flanks of the mountains,[40] which leads to extensive forestation. Snowfall typically totals more than 8 m (26 ft) annually, amounting to snow still being present as late as July or August. In warmer months, melted snow runs off into lakes, keeping them especially full.[1] Because the mountains are so tall, storm clouds may get stuck even as the rest of the storm moves onward, leading to snowstorms and freezing temperatures year-round. In extreme conditions, these storm cells might endanger hikers by means of strong winds, fog, snow, and rain that can potentially make hiking nearly impossible. On the eastern sides of the mountains, air warms as it drops, producingChinook winds, considerably lower precipitation, and less forested landscapes. Because of these conditions, temperatures on the western sides of mountains are steady, whereas temperatures on the eastern flanks fluctuate wildly.[41]
Goat Rocks obtained its name from a population ofmountain goats that can be observed around the mountain.[36] Other fauna includemarmots andpikas at high elevations.Deer andelk can be found below the timberline,[1] includingmule deer, mule deer-black-tailedhybrids,Roosevelt elk, andRocky Mountain elk that wereintroduced fromYellowstone National Park in 1913.Black-tailed deer are especially common.[4]
Old Snowy Mountain and Gilbert Peak, two of Goat Rocks's peaks, are frequented by hikers andmountaineers. Both are considered remote summits, although Old Snowy Mountain is the more accessible of the two.[42] This, coupled with its easier ascent, makes Old Snowy Mountain the more popular climb. There are several routes up the mountain, which take 5–6 hours, rising 1,097 m (3,599 ft) in elevation. Running for 23 km (14 mi) round-trip, Old Snowy can bescrambled orclimbed using glaciers, although a trail exists. From the summit, mountaineers can see Mount St. Helens and Mount Rainier in the distance.[42] Because this area has a lot of loose talus and rock, an avalanche hazard exists.[43]
The climb up Gilbert Peak was first completed by Fred G. Plummer in 1899.[19] It also rises 1,097 m (3,599 ft) in elevation, lasting 6–8 hours and running for 26 km (16 mi) round-trip. Because the routes are longer and more technically challenging due to loose rock, scrambling Gilbert is generally considered more difficult than Old Snowy Mountain. Most climbers opt to mount Gilbert early in the climbing season when snow levels are low.[43]
Recreational activities permitted by the Forest Service at the Wilderness include day hiking, horse riding, andbackpacking.[1] Because Goat Rocks is part of theNational Wilderness Preservation System, motor vehicles and means of transport are prohibited.[44] These include bicycles, wagons, motorboats, and helicopters. A free permit is required for entry to the wilderness.[45]
Mineral resources in the Goat Rocks area can be divided into three segments, each rich with certain minerals. The first two are named Packwood Glacier–McCall Basin and Glacier Basin,[46] and are located near past volcanic vents. These areas exhibit anomalous levels ofcobalt,copper,lead,molybdenum,nickel, andzinc, well-dispersed levels ofpyrite, and sporadic concentrations ofsilver.[47] Area C corresponds to the Clear Fork of theCowlitz River and lies along the area of contact between Goat Rocks volcano and older volcanoes to the east.[48] It is distinct from the other two study areas, featuring anomalous amounts ofbarium, cobalt, copper, andmanganese, as well as smaller quantities of lead, molybdenum, nickel, and zinc. Other minerals found in Area C includebarite,boron,cinnabar,mercury, pyrite, andtin in concentrates taken from stream-sediment. The water has high concentrations ofchlorine, copper,fluorine, and molybdenum, andaltered rocks containarsenic, lead, manganese, molybdenum, and zinc at especially high levels. The Goat Rocks vicinity seems to offer largebase metal deposits. Outside the area studied, coal has been identified at the Packwood and Cowlitz fields, and building stones and gravel are beingquarried to the north and west of the volcano. The Goat Rocks area's potential resources for oil and gas remain unidentified.[47] Because no volcanic activity has occurred during theHolocene (within the past 11,700 years), Goat Rocks has very little potential forgeothermal resources.[49]
Claims to threelode mines and a single coal mine were made within the Goat Rocks Wilderness, but theUnited States Bureau of Mines has no record of production from any of these claims. Historically, two claims have actually been staked in the area, the Mosquito lode near Walupt Lake in 1934, and later, the Glacier lode near Packwood Glacier in 1939. Neither show evidence of assessment work, and both deposits are now abandoned. Miners may have been drawn to the area by news of lode deposits containinggold, silver, and copper along breccia andshear zones to the north of the wilderness area.[50]
