1. Jeremy LongThe Black Canyon of the Gunnison Physical Geography Spring 2012

2. Geologic HistoryThe Black Canyon of the Gunnison has a long and complex history. Asfar as we can see the major factors involved with forming the canyonhave their roots in the Pre-cambrian Era. This is when we had theforming of the metamorphic rock that the Gunnison river has cut through.During the early Tertiary period the Gunnison uplift occurred which raisedthe base metamorphic rock up. This altered the drainage pattern of theoriginal basin that drained into a large ancient lake to the west.(Geological Survey...) 3. The early Tertiary period (1) the Gunnison uplift, (2) the Sawatch Range, (3) large ancient lake covering a large portion of western Colorado and eastern Utah. (Geological Survey...) 4. Middle Tertiary PeriodDuring the middle Tertiary periodthe Gunnison uplift was largelyflattened as the Sawatch rangeeroded, burying the Gunnisonuplift. The drainage pattern wasfree to meander across thelarge flat basin. (GeologicalSurvey...) 5. Middle and Late TertiaryThis period is the defining period for the Black Canyon. A major period of volcanism forced the river south around the forming West Elk Mountains. This put the Gunnison river over the Gunnison uplift. This volcanism provided large sheet like deposits of rock that served to initially entrench the river. (Geological Survey...) 6. Today the Black Canyon (4) is firmly entrenched and cutting through some of the oldest hardest stone that has been exposed in the world.(Geological Survey...) 7. Fluvial Processes in the Black Canyon The Black Canyon of the Gunnison is a classic example of an entrenched river. This canyon is unusual due to its depth, width and rock type. Down cutting is accelerated in this canyon due to the rivers grade, about 13 meters a mile, and by a large stream load. The Gunnison River provides the mechanism for the formation of the canyon, and down cutting is much faster than valley widening. 8. Down cutting and KnickpointsKnick points can account for alarge portion of down cutting.As this knick point undermines,the rock on top breaks awayand thus the knick point travelsupstream. Stream load andabrasive erosion accounts forsome of the down cutting butknick points do the most visiblework. 9. Mass WastingDue to the hard stone that formsthe canyon walls the mainforms of mass wasting arerockfall from frost wedging andland slides. Often the rockfallforms talus cones at the base ofsteep slopes. Here in thisimage several forms of masswasting are present, rockfall onthe right side with the harderstone forming steeper walls.Also, on the left the angle ofrepose is not as steep, and thematerials is not as hard, so landslide and general erosion arelikely the active agents. 10. Transportation Here the idea of transportation can be easily visualized. The Gunnison is constantly moving material downstream. On the right talus slopes are making their way to the river below. This movement and landslides bring the material down to the river to be transported downstream. This process has moved 25 cubic miles of material out of the canyon. 11. BibliographyGeological Survey Bulletin 1191. Black Canyon of the Gunnison: Today and Yesterday. U.S.G.S. March 28, 2006. Web. April 3rd, 2012.http://www.nature.nps.gov/water/Homepage/Black_canyon.cfmhttp://summitvoice.files.wordpress.com/2011/04/black.jpg?w=300&h=263http://images.nationalgeographic.com/wpf/media-live/photos/000/037/cache/blackhttp://tlc.howstuffworks.com/family/black-canyon-national-park-ga.htmhttp://en.wikipedia.org/wiki/File:Black_Canyon_of_the_Gunnison,_June_2010.jpgv