Hogg Rock is a tuya volcano and lava dome in the Cascade Range of northern Oregon, United States, located close to Santiam Pass. Produced by magma with an intermediate andesite composition, it has steep slopes and thick glassy margins. Hogg Rock exhibits normal magnetic polarity and is probably about 80,000 years old. Hogg Rock lies south of Three Fingered Jack and north of Hayrick Butte, a somewhat larger tuya of similar age and composition. A tuya is a type of subglacial volcano, formed when lava erupts underneath an overlying glacier or ice sheet and then melts through to the surface and pools, producing the flat plateau on top with near-vertical walls along the ice-contact margin as the lava cools and hardens. It is a historic landmark, with the remnants of Colonel T. Egenton Hogg's Oregon Pacific Railroad, the Santiam Lodge, and a quarry. The mountain offers snowshoe and snowmobile trails, and its summit provides views of the surrounding area including volcanoes like the Black Butte stratovolcano, Mount Washington, Sand Mountain, and Potato Hill.
Geography Hogg Rock is located in Linn County, in the U. S. state of Oregon. It is close to Santiam Pass, by the Hayrick Butte tuya, another feature produced from the interaction of volcanic eruptive materials with glaciers. It is close to the Mount Jefferson Wilderness, near where Oregon Route 22 and US Highway 20 intersect with the Cascade Range at Santiam Pass, and sits next to Oregon Route 126. Hogg Rock lies about 16 miles (25 km) north of Collier Cone, a cinder cone at the northern side of the base of the North Sister. The United States Geological Survey considers Hogg Rock part of the Three Fingered Jack quadrangle, while Siebert, Simkin, and Kimberly (2010) list it as a volcanic cone of Three Fingered Jack. Hogg Rock lies south of Three Fingered Jack and north of Hoodoo Butte and Hayrick Butte. According to the Geographic Names Information System, the volcano has an elevation of 4,823 feet (1,470 m).
Ecology The Oregon Department of Fish and Wildlife determined in the early 1990s that there was potential for peregrine falcon nests at Hogg Rock, though it was considered low-quality habitat because of its lack of suitable ledges and high amounts of human disturbance. Wildflowers and bracken ferns occur along roadways. The area has previously been affected by fires.
Geology
North Sister and Mount Washington mark isolated volcanic centers among the highly mafic (rich in magnesium and iron) platform of the central High Cascades. About 4.5 million years ago, eruption of mafic lava filled a subsiding Pliocene depression, creating the modern mafic edifice of the High Cascades. Compared to the eruptive products at and near North Sister, lava deposits at Mount Washington have a greater abundance of incompatible elements (elements unsuitable in size and/or charge to the cation sites of the minerals of which it is included.) Hogg Rock shows more similarity to the basaltic andesite deposits at North Sister, which are poorly enriched in incompatible elements. The part of the High Cascades that extends south from Mount Jefferson to Santiam Pass includes shield volcanoes, lava domes, and cinder cones. The high elevation of Matuyama-aged rocks east of Santiam Pass, coupled with exposure of Brunhes-aged rocks to the west, imply the presence of a northward-trending normal fault. Part of a mostly mafic chain of volcanoes between the Three Sisters and Mount Jefferson, Hogg Rock has magma with an intermediate composition. A tuya, Hogg Rock is also considered a small lava dome with the flat top typically observed for tuya volcanoes. Unlike most lava domes in the Cascades, which are made of dacite or rhyodacite, Hogg Rock is comprised by andesitic lava. It is thick with steep sides that have glassy margins between 3.3 to 19.7 feet (1 to 6 m) in thickness,[a] and the rock forming the dome is heavily jointed. Andesite forming Hogg Rock has an aphyric, only slightly porphyritic texture, with plagioclase, orthopyroxene, and olivine phenocrysts. Along with Hayrick Butte, the silica content for Hogg Rock measures about 59–60 percent. The volcano has been eroded by glaciers. It was formed during the Pleistocene, with an approximate age of roughly 80,000 years according to Deligne et al. (2017), corresponding to the Wisconsin glacial period; Hill and Priest (1992) assign it an age of 90,000 years ± 20,000 years, while Sherrod et al. argue that its age by K–Ar dating is 80,000 years ± 20,000 years. The volcano exhibits a normal magnetic polarity. Santiam Pass has been assessed for its geothermal energy potential, and there is a drill corehole extending to a depth of 3,040 feet (930 m) south of the highway area. In addition to the expected basaltic andesite lava and a number of dikes, the core also detected unusual basalt, andesite, and coarse sediment indicative of debris flows. The dating for these samples cannot be confirmed because of the close proximity of Brunhes-aged dikes, which likely heated nearby rock and caused the loss of radiogenic argon.
… excerpt ends here. Continue reading the full article.
