| Mount Thomson | |
|---|---|
 Mount Thomson | |
| Highest point | |
| Elevation | 6,554 ft (1,998 m)[1] |
| Prominence | 1,514 ft (461 m)[1] |
| Parent peak | Chikamin Peak[2] |
| Isolation | 2.33 mi (3.75 km)[2] |
| Coordinates | 47°28′20″N121°21′39″W / 47.472323°N 121.360711°W /47.472323; -121.360711[1] |
| Geography | |
  Mount Thomson Location in Washington Show map of Washington (state) Mount Thomson Mount Thomson (the United States) Show map of the United States | |
| Country | United States |
| State | Washington |
| County | King |
| Protected area | Alpine Lakes Wilderness |
| Parent range | Cascade Range |
| Topo map | USGSChikamin Peak |
| Geology | |
| Rock type | Keechelusandesite |
| Climbing | |
| First ascent | 1917 Joe Hazard, B. French[3] |
| Easiest route | Scrambling East Ridge |
Mount Thomson is a prominent 6,554-foot-elevation (1,998-meter) mountainsummit in easternKing County ofWashington state.[4]
Mount Thomson is part of theCascade Range and is a half-mile east of the crest of the range. Thomson is situated 4 mi (6.4 km) northeast ofSnoqualmie Pass in theAlpine Lakes Wilderness, on land managed byMount Baker-Snoqualmie National Forest. Precipitationrunoff on the mountain drains into the Middle Fork ofSnoqualmie River. The nearest peak isAlaska Mountain 0.81 mi (1.30 km) to the southeast, and the nearest higher peak isChikamin Peak, 2.08 mi (3.35 km) to the east.[1] The mountain was named forReginald Heber Thomson (1856-1949), a Seattle city engineer who reshaped the face ofSeattle.[3] This landform's toponym was spelled "Thompson" until the correct spelling was officially adopted in 1981 by theU.S. Board on Geographic Names.[4] Thefirst ascent of the peak was made in 1917 by Joe Hazard and B. French.
Mount Thomson is located in themarine west coast climate zone of western North America.[3] Mostweather fronts originating in the Pacific Ocean travel northeast toward the Cascade Mountains. As fronts approach, they are forced upward by the peaks of the Cascade Range, causing them to drop their moisture in the form of rain or snow onto the Cascades (Orographic lift). As a result, the west side of the Cascades experiences high precipitation, especially during the winter months in the form of snowfall. Because ofmaritime influence, snow tends to be wet and heavy, resulting in highavalanche danger.[3] During winter months, weather is usually cloudy, but due to high pressure systems over the Pacific Ocean that intensify during summer months, there is often little or no cloud cover during the summer.[3] The months of July through September offer the most favorable weather for viewing or climbing this peak.
The Alpine Lakes Wilderness features some of the most rugged topography in theCascade Range with craggy peaks and ridges, deepglacial valleys, andgranite walls spotted with over 700 mountain lakes.[5] Geological events occurring many years ago created the diverse topography and drastic elevation changes over the Cascade Range leading to the various climate differences.
The history of the formation of the Cascade Mountains dates back millions of years ago to the lateEocene Epoch.[6] With theNorth American Plate overriding thePacific Plate, episodes ofvolcanic igneous activity persisted.[6] In addition, small fragments of theoceanic andcontinental lithosphere calledterranes created theNorth Cascades about 50 million years ago.[6]
During thePleistocene period dating back over two million years ago, glaciation advancing and retreating repeatedly scoured and shaped the landscape.[6] The last glacial retreat in the Alpine Lakes area began about 14,000 years ago and was north of the Canada–US border by 10,000 years ago.[6] The U-shaped cross section of the river valleys is a result of that recent glaciation.Uplift andfaulting in combination with glaciation have been the dominant processes which have created the tall peaks and deep valleys of the Alpine Lakes Wilderness area.
Mountains portal