The Windows Section: Arches National Park
A
cache
by minerals44
Hidden:
11/17/2006
Size:
 (Not chosen)
Difficulty:
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(1 is easiest, 5 is hardest)
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You will visit an example of a typical Entrada Sandstone arch, one
of more than 2000 in the Park. Bowing and uplifting of sandstone
layers created vertical cracks that gradually eroded into “fins”.
Water seeped into the cracks, froze there, and the ice “wedged” off
pieces of rock. Wind and water continued their attack over
millennia. Some of the fins collapsed of their own weight, while
others having just the right hardness and geometry, evolved into
arches.
Directions:
South Window
From Hwy. 191 enter Arches National Park. You should stop at the
Visitors’ Center on the way into the park to pick up descriptive
pamphlets and see the exhibits. Do not miss the excellent film
shown in the new auditorium that describes the geology of rock
arches.
Follow the road past Balanced Rock, turning right at ~9.2 mi.
Proceed another 2.5 mi. to the parking area. The trail goes to the
North and South Windows and Turret Arch.
Supplies: Water, sunscreen, camera.
Alcove: An Arch "Wanna'be"
Learning Objectives:
- To become familiar with the terms “fins”, “joints” and
“evaporite”.
- To understand how arches and alcoves are formed.
Fins on a TOPO Map
The Entrada Sandstone lies atop a massive body of salt that
formed in the Paradox Basin ~250 million years ago. The salt is
water soluble and plastic. It migrated as the weight of deposited
sediments pressed down on it. The overlying rocks bowed upward into
an inverted “U” (an anticline). Under this stress the sedimentary
rock fractured into parallel slices known as "fins". The fractures
are called "joints", weakened places subject to erosion.
Alcoves and arches form as these sandstone fins are worn away by
chemical weathering (dissolution of the calcium carbonate
that cements the sand grains) and mechanical weathering
(water, wind, ice, abrasion)
Educational Requirement: To get
credit for this EarthCache you must email us your answer to any one
of the Study Questions and let us know how many people were in your
party.
Study Questions: ("Azimov-rated"). Note: Graduate- and
Ph.D.-level questions may take a bit of looking on the www.
- College-Bound AP Describe how “fins” were formed.
- College-Bound AP (Virtual survey) Double-click on the
cache map above and select the "hybrid" or "satellite" view in
Google Maps. As you zoom in on the cache, look for evidence of fins
nearby?
- College-Bound AP Describe the forces that erode
fins.
- Freshman Do you think differences between the two
members of the Entrada sandstone contribute to the formation of the
arches?
- Graduate Where did the salt in the Paradox evaporite
beds come from?
- Ph.D. What chemical compounds (minerals) are included
under the general term “evaporites”?
- Ph.D. As you pass the intersection of Hwy. 279 and Hwy.
191 north of Moab there is a sign which exists because of the
Paradox Evaporites. What does it say? Explain. [Major
hint!]
Links and Resources:
- Wikipedia on Salt
Domes
- Wikipedia on
Evaporites
- How
arches are formed.
- Park Service
Descriptions
-
Technical paper
-
Really technical paper
- Anticlines,
synclines and monoclines.
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Current time: 11/21/2009 11:12:33 PM Last Updated: 11/19/2009 9:46:29 PM Rendered: From Database Coordinates are in the WGS84 datum
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