Goat Rocks

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This article is about the stratovolcano. For the lava dome, see Goat Rocks dome.
Goat Rocks
Gilbert 14A.JPG
The Goat Rocks, with Gilbert Peak at upper left
Elevation 8,184 ft (2,494 m)
Location
Location Lewis / Yakima counties, Washington, U.S.
Range Cascade Range
Coordinates 46°29′19″N 121°24′21″W / 46.48861°N 121.40583°W / 46.48861; -121.40583Coordinates: 46°29′19″N 121°24′21″W / 46.48861°N 121.40583°W / 46.48861; -121.40583
Topo map USGS Old Snowy Mountain, Walupt Lake
Geology
Type Dissected Stratovolcano
Age of rock 3.2 million - 730,000 years
Volcanic arc Cascade Volcanic Arc
Climbing
First ascent Fred G. Plummer, 1899
Easiest route Scrambling

The Goat Rocks are a series of rugged volcanic peaks in the Cascade Range, roughly between Mount Rainier and Mount Adams in southern Washington state. They are named after the numerous mountain goats which live in the area, and are at the core of the eponymous Goat Rocks Wilderness.

Geography and geology[edit]

Goat Ridge. The base of Mount Adams is visible.
Old Snowy Mountain from the north, with the snow-covered McCall and Packwood Glaciers flanking the peak

The Goats Rocks complex is located in southern Washington, 70 miles (113 km) west of Yakima,[1] at latitude 46.50° N and longitude 121.45° W.[2] 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.[3] It is a zone of intermittent volcanism which has produced many small volcanic vents. Over time, overlap occurred, and these vents now make up the Mount Adams volcanic field, Indian Heaven, and parts of Goat Rocks.[4] Situated in the eastern portion of the Cascade Range, Goat Rocks lies at the northwest corner of the Klickitat River basin.[5] The Cascade Volcanoes in Washington are restricted to four belts; Goat Rocks forms one segment of the north–south trending Mount Adams belt that includes Tumac Mountain, Adams, and the King Mountain Fissure Zone. This belt contains the second most volcanoes of the four, and its volcanoes are made predominantly of calc-alkalic to tholeiitic to basaltic andesite lava.[6] Goats Rocks and its vicinity are underlain by pre-Tertiary greywacke and argillite, and these deposits are cut by several prominent northward-trending faults.[7]

Together with Mount Adams, Mount Rainier, and Mount St. Helens, the Goat Rocks complex forms a triangular array of volcanoes 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 of sedimentary rock against a continental margin.[8] However, Hill et al. (2009) dismiss this view as it proves inconsistent with maps made from magnetotelluric readings of the area. Instead, they propose that the region's volcanism has caused partial melting of the crust.[9]

Eruptive history[edit]

Goat Rocks is composed of the eroded remnants of a stratovolcano, where activity began approximately 3.2 million years ago during the Pliocene epoch. At first, it erupted silicic lava that included felsic rocks like rhyolite. One of these events produced 650 m (2,133 ft) of tuff that remains, exposed, on the east flank of the existing mountain. 3 million years ago Goat Rocks shifted to mafic volcanism, erupting olivine and basalt. As eruptions continued into the Pleistocene epoch, the lava flows became more andesitic, containing mostly pyroxene with phenocrysts as well as hornblende minerals. These andesitic flows formed the volcano between roughly 2.5 and 0.5 million years ago,[2] which may have resembled contemporary Mount Rainier.[10] Several eruptions had very high volumes, perhaps because multiple satellite vents contributed to eruptions,[7] and extended far from the volcano.[2] Approximately 1 million years ago, Goat Rocks generated an andesitic lava flow extending 80 km (50 mi) down the Naches and Tieton Rivers, which has been recognized as the longest andesite flow on Earth.[2] Many of the flows immediately surrounding the volcano have since been cut by intrusive dikes, 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. Eruptive activity continued at Old Snowy Mountain into the middle to late Pleistocene, yielding hornblende andesite lava flows that were glaciated in the Cispus River valley. Hornblende andesite can also be found on top of the highest point in Goat Rocks, Gilbert Peak. Whether Old Snowy Mountain is a vent of Goat Rocks or an independent volcano remains unclear.[1]

Goat Rocks is classified as an extinct volcano, as its last eruptive activity finished during the early Pleistocene. The oldest Cascade stratovolcano formed after the Columbia River Basalt Group, it is roughly equal in volume to Mount St. Helens and smaller in volume than Mount Baker, at approximately 14.4 cu mi (60 km3). Rough estimates place the composition of the volcano as 40% tuff and breccia.[11] The remains of its lava flows can be found in the Tieton, Klickitat, and Cispus riber valleys, their elevation reversed by erosion to make them resemble ridges. These flows have been thoroughly eroded, but testify to the volcano's previous size.[12]

Hogback Mountain, a shield volcano north of Goat Rocks and south of White Pass, was identified by Siebert et al. (2010) as a satellite vent of Goat Rocks.[13] 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.[1] Eruptions from Goat Rocks formed a spread-out volcanic field populated by small lava domes to the north, which is 18.6 by 9.3 miles (29.9 by 15.0 km).[12]

Glaciation[edit]

Goat Rocks is similar to other nearby, ancient volcanoes in that it has undergone extensive erosion,[14] and much of the leftover rock has been partially covered by younger rocks.[11] Once the volcanic eruptions came to an end, the ongoing forces of glacial erosion stripped away the outer layers of volcanic ash deposits and lava flows,[15] uncovering the rocky lava spines where magma had cooled and hardened within the conduits of the volcano. The current eroded volcano has numerous summits reaching about 8,000 ft (2,400 m). The Goat Rocks area is notable for its extensive glaciers, despite the modest elevation and southerly location relative to the rest of the Washington Cascades. Four glaciers mantle the north and northeast slopes of the peaks: Conrad Glacier, McCall Glacier, Meade Glacier, and Packwood Glacier, along with numerous smaller permanent snowfields.

The remnant core of the Goat Rocks Volcano is Egg Butte, located north of Old Snowy Mountain in the valley carved by the ice age Packwood Glacier. Similar to the lava spines remaining on the ridges to the south and east of Old Snowy Mountain, the dense core became exposed after the Packwood Glacier removed the softer ash and broken flows around it. At the base of the valley lies Packwood Lake, formed behind the terminal moraine created by the [ice age] Packwood Glacier, evidence of the large amount of volcanic material stripped away by the glacier.

Goat Ridge panorama with Old Snowy Mountain on the left obscured by cloud cover.

Major peaks[edit]

The elevation in the Goat Rocks vicinity varies from 3,000 ft (914 m) to 8,201 ft (2,500 m) at its highest point, Gilbert Peak. Because of extensive glaciation and erosion, the peaks of Goat Rocks are at most moderate in height.[15]

Gilbert Peak (Mount Curtis Gilbert) 8,201 ft (2,500 m)[15]
Old Snowy Mountain 7,880 ft (2,402 m)[16]
Ives Peak 7,920 ft (2,414 m)[17]
Tieton Peak 7,772 ft (2,369 m)[18]
Johnson Peak 7,487 ft (2,282 m)[19]
Bear Creek Mountain 7,341 ft (2,238 m)[20]
Hogback Mountain 6,793 ft (2,071 m)[21]

Wilderness[edit]

Main article: Goat Rocks Wilderness
Looking down at a herd of goats from the Pacific Crest Trail

Land surrounding Goat Rocks was first protected by the United States Department of Agriculture in February 1931, when approximately 44,500 acres (18,009 hectares) was set aside for preservation. In 1935, this was increased to 72,440 acres (29,315 hectares) of land, then to 82,680 acres (33,459 hectares) in 1940. In 1964, the United States Congress created the Goats Rock Wilderness as part of the National Wilderness Preservation System, delegating its management to the United States Forest Service. Since additional land was incorporated in 1984,[22] it now encompasses 108,096 acres (43,745 hectares) between Mount Rainier and Mount Adams, straddling the Gifford Pinchot and Okanogan-Wenatchee national forests.[23] It is bordered by the Yakama Indian Reservation to the southeast.[22]

The wilderness ranges from 3,000 to 8,201 ft (914 to 2,500 m) in elevation, featuring alpine tundras with glaciers, small lakes, and ponds, as well as 15 different routes that amount to 120 mi (193 km) of trails. One of these trails constitutes the highest segment of the famous Pacific Crest Trail in Washington,[24] running for 31.1 mi (50 km) north–south through the middle of the wilderness area.[23] Because this route is located at such a high elevation, its hikers may experience violent storms that could be dangerous for unprepared parties.[25] Much of the wilderness is located above the timberline, offering views of alpine scenery.[22]

Climbing and recreation[edit]

Old Snowy Mountain and Mount Gilbert, two of Goat Rocks's peaks, are frequented by hikers and mountaineers. Both are considered remote summits, although Old Snowy Mountain is the more accessible of the two.[26] 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 3,600 ft (1,097 m) in elevation. Running for 14 mi (23 km) round-trip, Old Snowy can be scrambled or climbed using glaciers, although a trail exists. From the summit, mountaineers can see Mount St. Helens and Mount Rainier in the distance.[26] Because this area has a lot of loose talus and rock, an avalanche hazard exists.[27]

The climb up Mount Gilbert also rises 3,600 ft (1,097 m) in elevation, lasting 6–8 hours and running for 16 mi (26 km) 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.[27]

Recreational activities permitted by the Forest Service at the Wilderness include day hiking, horse riding, and backpacking.[15] Because Goat Rocks is part of the National Wilderness Preservation System, motor vehicles and means of transport are prohibited.[28] These include bicycles, wagons, motorboats, and helicopters. A free permit is required for entry to the wilderness.[29]

Climate and wildlife[edit]

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 150 in (381 cm) in rainfall annually) on the western flanks of the mountains,[30] which leads to extensive forestation. Snowfall typically totals more than 25 ft (8 m) 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.[15]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, producing Chinook 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.[31]

Goat Rocks obtained its name from a population of mountain goats that can be observed around the mountain.[22] Other fauna include marmots and pikas at high elevations. Deer and elk can be found below the timberline,[15] including mule deer, mule deer-black-tailed hybrids, Roosevelt elk, and Rocky Mountain elk that were introduced from Yellowstone National Park in 1913. Black-tailed deer are especially common.[3]

See also[edit]

Notes[edit]

  1. ^ a b c Wood 1992, p. 161.
  2. ^ a b c d Wood 1992, pp. 160.
  3. ^ a b Barstad, p.2.
  4. ^ Topinka, Lyn (February 27, 2002). "Description: Volcanic Fields and Centers near Mount Adams, Washington". United States Geological Survey. Retrieved April 24, 2010. 
  5. ^ "The Volcanoes of Lewis and Clark: April 15, 1806". United States Geological Survey. July 2004. Retrieved May 19, 2015. 
  6. ^ Korosec et al. (1983), pp. 183–184.
  7. ^ a b Church and Close (1984), p. 1063.
  8. ^ Commission on Geosciences, Environment and Resources 1994, p. 39.
  9. ^ Hill 2009.
  10. ^ Korosec et al. (1983), p. 213.
  11. ^ a b Smith, p. 10.
  12. ^ a b Smith, p. 9.
  13. ^ Siebert et al. (2010), p. 408.
  14. ^ Smith, p. 3.
  15. ^ a b c d e f "Wilderness: Goat Rocks - Gifford Pinchot". United States Forest Service. 2015. Retrieved May 18, 2015. 
  16. ^ "Old Snowy Mountain, Washington". Peakbagger.com. Retrieved May 18, 2015. 
  17. ^ "Ives Peak, Washington". Peakbagger.com. Retrieved May 18, 2015. 
  18. ^ "Tieton Peak, Washington". Peakbagger.com. Retrieved May 18, 2015. 
  19. ^ "Johnson Peak, Washington". Peakbagger.com. Retrieved May 18, 2015. 
  20. ^ "Bear Creek Mountain, Washington". Peakbagger.com. Retrieved May 18, 2015. 
  21. ^ "Hogback Mountain, Washington". Peakbagger.com. Retrieved May 18, 2015. 
  22. ^ a b c d "Gifford Pinchot National Forest: Goat Rocks Wilderness". United States Forest Service. 2015. Retrieved May 20, 2015. 
  23. ^ a b "Goat Rocks Wilderness: General". Wilderness.net. United States Forest Service and the University of Montana. Retrieved May 20, 2015. 
  24. ^ Barstad, p. 75.
  25. ^ Barstad, p. 76.
  26. ^ a b Smoot, p. 345.
  27. ^ a b Smoot, p. 347.
  28. ^ "Gifford-Pinchot National Forest Wilderness Regulations". United States Forest Service. 2015. Retrieved May 20, 2015. 
  29. ^ "Goat Rocks Wilderness: Area Management". Wilderness.net. United States Forest Service and the University of Montana. Retrieved May 20, 2015. 
  30. ^ Barstad, p. 1.
  31. ^ Barstad, pp. 1–2.

References[edit]

  • Barstad, Fred (2004). Hiking Washington's Goat Rocks Country: A Guide to the Goat Rocks and Lewis and Cispus River Regions of Washington's Southern Cascades. Globe Pequot Press. 
  • Commission on Geosciences, Environment and Resources; U.S. Geodynamics Committee; National Research Council, Division on Earth and Life Studies (1994). Mount Rainier:: Active Cascade Volcano. National Academies Press. 
  • Smoot, Jeff (2002). Climbing Washington's Mountains: Summit Hikes, Scrambles and Climbs in Washington's Cascade and Olympic Mountain Range. Globe Pequot Press. 
  • Wood, Charles A.; Kienle, Jurgen, eds. (1992). Volcanoes of North America: United States and Canada. Cambridge, England: Cambridge University Press. ISBN 978-0-521-43811-7.