Jack Mountain is the 17th highest mountain in

Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered o ...

state. It is one of the 10 non-volcanic peaks in Washington State over . It towers dramatically over the south end of Ross Lake, rising above the lakeshore in only . Nohokomeen Glacier nearly fills the

cirque A (; from the Latin word ') is an amphitheatre-like valley formed by glacial erosion. Alternative names for this landform are corrie (from Scottish Gaelic , meaning a pot or cauldron) and (; ). A cirque may also be a similarly shaped landform ...

on the upper north slopes of the mountain.

History

Jack Mountain was first described by surveyor Henry Custer in 1859, and was named for prospector Jack Rowley who was active on Canyon Creek. The first recorded ascent of Jack Mountain was made in 1904 by topographer E.C. Barnard. By the 1980s climbing routes had been established on most ridges, glaciers, and directions, seven in total. Most are but some involve true technical climbing. All are long routes with a great deal of vertical gain, meaning most parties take three to four days to climb the mountain.

Geology

Rock Types

The mountain is composed mostly of

Metavolcanic rock Metavolcanic rock is volcanic rock that shows signs of having experienced metamorphism. In other words, the rock was originally produced by a volcano, either as lava or tephra. The rock was then subjected to high pressure, high temperature or both ...

and

Metasedimentary rock In geology, metasedimentary rock is a type of metamorphic rock. Such a rock was first formed through the deposition and solidification of sediment Sediment is a naturally occurring material that is broken down by processes of weathering and ...

from the Hozameen Group. Most predominant is Greenstone from the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...

periods. Most surface material is heavily eroded, by water Glacier ice. The lower flanks of the mountain in the Devils creek basin Maine sedimentary rock from the lower

Cretaceous period The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of t ...

, part of the Harts Pass Formation. The lower flanks of the mountain on the Ross lake side are composed of many diffent rock types including

Orthogneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures an ...

Ultramafic rock Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are composed ...

, low grade

Phyllite Phyllite ( ) is a type of foliated metamorphic rock created from slate that is further metamorphosed so that very fine grained white mica achieves a preferred orientation.Stephen Marshak ''Essentials of Geology'', 3rd ed. It is primarily compo ...

Tonalite Tonalite is an igneous, plutonic ( intrusive) rock, of felsic composition, with phaneritic (coarse-grained) texture. Feldspar is present as plagioclase (typically oligoclase or andesine) with alkali feldspar making up less than 10% of the total ...

, Continental glacier drift,

Diorite Diorite ( ) is an intrusive igneous rock formed by the slow cooling underground of magma (molten rock) that has a moderate content of silica and a relatively low content of alkali metals. It is intermediate in composition between low-silic ...

, and

Schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes o ...

Faults and Formation

The Jack Mountain area consists of one small

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...

, and a few other normal faults, none showing any seismic activity. Jack Mountain was created when the Hozameen Group was thrusted over the younger Harts Pass formation to the east. Most likely caused by the

Ross lake Fault The 10 kilometer wide Ross Lake fault zone (RLFZ) is part of a 500 kilometer long zone of high-angle faults in the North American Cordillera of Washington and Canada. The RLFZ consists of two major sets of faults. The eastern set of the Hozameen ...

to the west. The lower flanks of the mountain to the west were created by the Ruby Creek Heterogeneous plutonic belt.https://fortress.wa.gov/dnr/geology/?Theme=wigm, Surface geology map layer.Beckey, Fred W. Cascade Alpine Guide, Climbing and High Routes Pg 202, 203, 204, 205. Seattle, WA: Mountaineers Books, 2008.

Geographical features

Jack Mountain from Diablo Lake Vista Point

* Nohokomeen Glacier fills northwestern side of mountain * Northeast glacier steep and heavily crevassed small glacier * East glacier small pocket glacier on the east side * Northwest glacier, small hanging glacier west of summit ridge * Crater creek, main southside drainage * Devils creek, main northside drainage * Nohokomeen falls, May creek water fall over headwall * Roland creek is located on the steep westside, its tributary's hold many waterfall.

Routes

*Southeast Ridge first ascent John Anderson and Alan Kearney August 1977. Grade III, class 5.6 *Southeast route class 4 *East ridge first ascent Carl and Gordon Skoog July 16, 1984. Grade II, class 4. *Northeast Glacier first ascent

Fred Beckey Friedrich Wolfgang Beckey (14 January 1923 – 30 October 2017), known as Fred Beckey, was an American rock climber, mountaineer and book author, who in seven decades of climbing achieved hundreds of first ascents of the tallest peaks and best ro ...

, Dallas Kloke, Reed Tindall July 19, 1978. *North Ridge first ascent Joe Vance and Bill Weitkamp August 1, 1971. Grade II class 4 *Southwest Ridge class 4 *South Face class 4

References

External links

* * * {{Washington highest Mountains of Washington (state) Mountains of Whatcom County, Washington