Arches National Park

8th Grade Science• What is the purpose?

– To understand geology and understand how it relates to the red rock formations

• Objectives– Understand natural and cultural resources of our national

parks, surrounding areas and the earth as a whole. – Develop a wide range of environmentally responsible

activities in the outdoors to learn skills, judgment, confidence and sensitivity.

– Understanding the properties and the interconnected nature of Earth's systems, processes that shape Earth and Earth's history

Terms to Know

• Paradox Formation- underground salt bed• Arch- geological formation with a minimum 3

foot wide opening. • Pothole- basins or pools in sandstone that

collect rainwater and wind-blown sediment• Biological Soil Crust- Biological soil crust is a

living groundcover that forms the foundation of high desert plant life

How did the arches form?Arches National Park lies atop an underground salt bed called the “Paradox

Formation” which is responsible for the arches. Over millions of years, the salt bed was covered with the residue of floods and winds

as the oceans returned and evaporated. Much of this debris was cemented into rock.

Salt under pressure is unstable, and the salt bed below Arches began to flow under the weight of the overlying sandstones. This movement caused the surface rock to buckle and shift, thrusting some sections upward into domes, dropping others into surrounding cavities, and causing vertical cracks which would later contribute to the development of arches.

Water seeped into cracks and joints, washing away loose debris and eroding the "cement" that held the sandstone together, leaving a series of free-standing fins. During colder periods, ice formed, its expansion putting pressure on the rock, breaking off bits and pieces, and sometimes creating openings. With the right degree of hardness and balance, most of these openings have survived as the world famous formations of Arches National Park.

What do you mean, potholes?• Throughout Arches, naturally occurring sandstone basins called potholes collect rain water

and wind-blown sediment, forming tiny ecosystems where a fascinating collection of plants and animals have adapted to life in the desert. These potholes range from a few millimeters to a few meters in depth, and even the smallest potholes may harbor microscopic invertebrates.

• To survive in a pothole, organisms must endure extreme fluctuations in several environmental factors. Surface temperatures vary from 140 degrees Fahrenheit in summer to below freezing in winter.

• The most extreme conditions exist when a pothole is dry.• Desert precipitation falls at irregular intervals, and once water enters a pothole there is no

guarantee that there is enough for an organism to complete its life cycle. Most organisms living in potholes have very short life cycles, as brief as ten days, reducing the time water is required and allowing them to live in the shallow pools.

• After a pothole fills with water, the small ecosystem experiences many other changes. Water temperatures can be very high, while oxygen levels can be very low. As the pool shrinks from evaporation, its salinity increases and the pH changes. Many organisms are capable of surviving wide fluctuations in these factors, but for some these changes are an indication that the time for dormancy is near.

Biological what?• Biological soil crust is a living groundcover that forms the foundation of high desert

plant life. This knobby, black crust is dominated by cyanobacteria, but also includes lichens, mosses, green algae, microfungi and bacteria.

• Cyanobacteria, previously called blue-green algae, are one of the oldest known life forms. Extremely thick mats of these organisms converted the earth's original carbon dioxide-rich atmosphere into one rich in oxygen and capable of sustaining life.

• When wet, Cyanobacteria move through the soil and bind rock or soil particles, forming an intricate web of fibers. In this way, loose soil particles are joined together, and an otherwise unstable surface becomes very resistant to both wind and water erosion. Layers of abandoned sheaths, built up over long periods of time, can still be found clinging tenaciously to soil particles, providing cohesion and stability in sandy soils at depths up to 10cm.

• Nitrogen fixation is another significant capability of cyanobacteria. Cyanobacteria are able to convert atmospheric nitrogen to a form plants can use. This is especially important in desert ecosystems, where nitrogen levels are low and often limiting to plant productivity.

• Soil crusts have other functions as well, including an ability to intercept and store water, nutrients and organic matter that might otherwise be unavailable to plants.

Other important facts

• The major rock formations visible in the park today are the salmon-colored Entrada Sandstone, in which most of the arches form.

• Over 2,000 catalogued arches range in size from a 3 foot opening minimum to Landscape Arch which measures 306 feet from base to base

Resources

• Arches National Park: Official Site. Retrieved June 28, 2009, from: http://www.nps.gov/arch/index.htm

• Arches National Park: Natural Features and Ecosystems. Retrieved June 29, 2009, from: http://www.nps.gov/arch/naturescience/naturalfeaturesandecosystems.htm

Brain Teasers

• Here are a few quiz questions to test your knowledge

Question #1 Question #2 Question #3

Question #1

• What is the minimum width (in feet) to be considered an arch?

5

3

7

CORRECT!

• The minimum width to be considered an arch is 3 feet

INCORRECT

• Please review this information and try the question again.

Question #2

• Out of what stone do most of the arches form?

Entrada Sandstone

Limestone

Salt

Correct!!!

• The major rock formations visible in the park today are the salmon-colored Entrada Sandstone, in which most of the arches form.

Incorrect

• Please review the information and try the question again

Question #3

• What is the most extreme condition for a pothole?

wet

hot

dry

Correct!!!

• The most extreme conditions exist when a pothole is dry

Incorrect

• Please review the information and try the question again

Conclusion

• You did it! All of the quiz answers are now correct. I hope you better understand the Arches National Park formations and how they formed.