1 / 21

Canyons and Arches or: Why erosion is cool

Canyons and Arches or: Why erosion is cool. Angela Stickle March 5, 2007 Geology of the Desert SW. Canyons are cool. Erosion when water runs through dry regions with sedimentary rocks layers of varying resistance Formation due to natural tendency of rivers to reach a base line elevation

truda
Download Presentation

Canyons and Arches or: Why erosion is cool

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Canyons and Arches or: Why erosion is cool Angela Stickle March 5, 2007 Geology of the Desert SW

  2. Canyons are cool • Erosion when water runs through dry regions with sedimentary rocks layers of varying resistance • Formation due to natural tendency of rivers to reach a base line elevation • The larger the height difference between river and inlet into draining body, the more energy it will expend • = more erosion! • Energy expended in facilitating a speedy drop in elevation

  3. Canyon Forming processes • Stream Downcutting • Deepens the channel of a stream or valley • Removes material from bed or valley floor • How fast downcutting occurs depends on base level • Lateral Erosion • Widens a stream channel or valley • Most dominant if stream level is near the base level • If Elevation > Base level • Downcutting > Lateral erosion San Juan River, Utah

  4. Canyon Forming processes • Mass wasting • Aka: mass or slope movement • “geomorphic process by which soil, regolith and rock move downslope under gravity.” • Creep, slides, flows, etc

  5. Canyon Formation • Surface stripped by running water • Terraces formed in rocks of varying resistance • Vertical erosion predominates and alternating cliffs are formed through downcutting http://library.thinkquest.org/C005280/geoformation.htm

  6. Zion sediment deposition • Kaibab (Upper Permian), limestone • Moenkopi (lower triassic, 230 mya), mudstone, shales, siltstones • Chinle (upper Triassic), includes petrified woods etc • Moenave (Lower Jurassic), siltstone, mudstone, fine sandstone • Kayenta (Lower Jurassic), sand and siltstone

  7. Zion sediment deposition • Navajo (Low to Mid Jurassic), sandstone • Temple Cap (Middle Jurassic), clay and silt • Carmel (Middle Jurassic), limestone • Dakota (Lower Cretaceous), sandstone

  8. Zion and Kolob Canyons • This area includes 9 known exposed formations in Zion • Represents 150 MY, mostly mesozoic aged, sedimentation Kolob Canyons from end of Kolob Canyons Road, showing red-orange Navajo Sandstone

  9. Zion National Park • Varying depositional environments: • Warm, shallow seas • Streams and lakes • Deserts and near shore environments • Uplift of the Colorado plateau exposed sediments to erosion • Much later, lava flows and cinder cones covered part of the Zion area

  10. Zion National Park • Elevated plateau with sedimentary formations dipping gently east • Oldest strata exposed along the Virgin River • Youngest strata exposed in Kolob Canyons Canyons in Zion Nat’l Park

  11. Zion canyon • About 6000 feet of sediment have been removed from Dakota Sandstone • Continuing erosion of Navajo sandstone • At head of Zion canyon, Virgin River reaching Kayenta Formation, eroding the shale and undermining the overlaying sandstone • Causes collapses • Widens Canyon • Geologists estimate the Virgin River will cut ~1000 ft before it loses ability to transport sediment Temple of Sinawava

  12. Zion Canyons Zion Canyon Canyon Overlook

  13. Natural Arches • “A rock exposure that has a hole completely through it formed by the natural, selective removal of rock, leaving a relatively intact frame.” • Must be made of exposed rock! • Actually have a hole… • Hole formed from natural removal of rock (typically erosion, but lava flow happens too..)

  14. Natural Bridges • Natural Bridges are types of Natural Arches • Distinguished by: • A current of water (e.g. stream) formed the hole or is running through it • It is being used as a bridge • Looks like a bridge

  15. Several types • Alcove Natural Arch • Buttress Natural Arch • Meander Natural Bridge • Pothole Natural Arch • Shelter Natural Arch • Waterfall Natural Bridge

  16. Alcove Natural Arch • Occurs on or next to a vertical cliff face • Only forms where vertical joint exists behind and parallel to face • Very common, relieves stress • Kolob Arch in Zion • Eroded into Navajo sandstone • Span: 287’, second largest in the world!

  17. Meander Natural Bridge • Associated with active stream or streambed • Opening in a semicircle and the lintel is arched • Wall collapse also important feature (creates semi-circle aperture) • Rainbow Bridge • Largest natural bridge in the world • Opening 246’ high • Lake Powell, Utah

  18. Lateral Stream Piracy • Two water courses separated at a point by a thin rock barrier • Barrier must be breached!! • Water of one stream is ‘stolen’ by the other • Two occasions: • Neck of an incised meander • Two tributaries running closely parallel

  19. Capitol Reef Canyons

  20. Capitol Reef Arches Muley Twist Canyon, Capitol Reef Hickman Bridge, Capitol Reef

  21. References • www.wikipedia.org • http://www-geoimages.berkeley.edu/Waterfalls/ZionCanyon/TempleSinawavaL.html • http://www.zionparkmotel.com/images/zion-national-park.jpg • http://www.terragalleria.com/images/np-plateau/zion0787.jpeg • http://www.naturalarches.org/archinfo/faq.htm#whatis • http://darkwing.uoregon.edu/~mobar/images/capreef.jpg • http://www.americansouthwest.net/utah/photographs700/capvalley.jpg • http://www.so-utah.com/archcany/arches/delicate.jpg • http://www.travelwest.net/parks/zion/images/zion-canyon.jpg • http://www.aztecdaytrips.com/images/rooftop.jpg • http://www.computersforart.org/create/arch/big/computer_arch_07.jpg

More Related