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In order to count this Earthcache as a find, you must complete the following tasks and email the answers to me.
1. What is the elevation? Based on this information, what can you can conclude is the elevation of the intake/recharge area of the aquifer?
2. Estimate the height to which rocks were pushed up in this area when the tectonic plates collided.
3. Describe the rock you see at the surface. How do you think this rock compares to the rock that makes up the foundation of the aquifer?
4. Is the flow from this spring closer to a “First Magnitude Spring” or an “Eighth Magnitude Spring”?
5. Is this spring intermittent or continuous?
6. If the water table in this area fell below the level of the spring, would this spring continue to be a flowing spring?
This Earthcache is located at a pull-off area along Vanocker Canyon Road in the Black Hills. Enjoy the beautiful scenery and taste the water if you dare. Enjoy!
The Black Hills are an isolated mountain range spanning from western South Dakota and into Wyoming. Geologists describe the region as a geological anomaly, calling it an “island of trees in a sea of grass.” The Black Hills is home to the tallest peaks in continental North America east of the Rocky Mountains.
The current landscape of the Black Hills is the result of tectonic activity. The time period between 2.6 million and 65 million years ago was marked by worldwide tectonic activity. During this time period, worldwide tectonic activity occurred. In some parts of the world, tectonic plates split apart from one another, while in other areas, including the Black Hills, the plates collided.
On Earth, there are currently eight major plates and many minor plates. Tectonic plates move in relation to each other at one of three types of plate boundaries: convergent or collisional boundaries, divergent boundaries or spreading centers, and transform boundaries. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along plate boundaries.
Transform boundaries occur where plates grind past each other along transform faults. Plates moving along a transform boundary cause earthquakes. The San Andreas Fault in California is a good example of a transform boundary.
Divergent boundaries occur where two plates slide apart from each other. The space created by these two plates moving apart is filled with new crustal material formed from molten magma that forms below. Mid-ocean ridges, such as the Mid-Atlantic Ridge, and active zones of rifting, such as Africa’s Great Rift Valley, are both examples of divergent boundaries.
Convergent boundaries occur where two plates slide toward each other, forming either a subduction zone, if one plate moves underneath the other, or a continental collision, if the two plates contain continental crust. This type of boundary is responsible for the creation of mountains (continental collision) and volcanic activity (subduction zone).
About 70 million years ago, at a convergent boundary in the Hills, two plates collided and caused an uplift (rise) of the landscape and rock in the area. The majority of the rock that can be found in the area was deposited as sediments at the bottom of an ancient sea that covered the area between 1.6 and 2.5 billion years ago. These rocks are classified as sandstone and shale. Other rock is the result of volcanic activity, which occurred in the northern part of the hills near the same time as the collision of the two tectonic plates. This type of rock is known as granite. These rocks that make up the Black Hills--particularly the sandstone--serve as a solid foundation for the formation of aquifers. By definition, an aquifer is a body of permeable rock below the surface that can take in and hold groundwater and move it from one place to another. The groundwater held by the the aquifer makes its way to the surface via wells or springs. This groundwater provides the drinking water for the people who live, work, and visit the Black Hills. The water held by this aquifer also is pushed eastward and provides water to other areas up to 200 miles away.
The spring located at this location can be classified as an artesian spring. In order for an artesian system to develop, three geologic conditions are necessary. These conditions, according to James Monroe’s and Reed Wicander’s book The Changing Earth: Exploring Geology and Evolution, are “(1) The aquifer must be confined above and below by aquicludes [a zone of rock within the earth that restricts the flow of groundwater from one aquifer to another] to prevent water from escaping; (2) the rock sequence is usually tilted and exposed at the surface, enabling the aquifer to be recharged; (3) precipitation in the recharge area is sufficient to keep the aquifer filled” (359). The intake/recharge area of the aquifer in the Black Hills sits at a higher elevation than the rest of the aquifer. The rest of the rock foundation housing the aquifer dips downward, causing the water to move downhill and away from the intake area, gradually building up pressure. This build-up of pressure is in the confined aquifer is what causes the water to rise to the surface. When a well is drilled, the pressure is reduced, and the water is forced upward. An artesian spring occurs where there is a fault or fracture in the rock confining the aquifer. Just like a well, these fractures reduce the built-up pressure and force the water to the surface.
Artesian springs, such as the one at this location, are common around the periphery of the Black Hills. Springs are often classified by the volume of the water they discharge. The largest springs are called "First-magnitude." First-magnitude springs discharge water at a rate of at 748 gallons of water per second. The smallest flowing springs are called “Eighth-magnitude.” Eighth-magnitude springs discharge water at a rate of 0.12 gallons per minute.
Long ago, someone stuck a small pipe here and water from the artesian spring has been gushing ever since.
Resources:
Monroe, James S., and Reed Wicander. The Changing Earth: Exploring Geology and Evolution. 4th ed. Belmon, CA: Thomson Brooks/Cole, 2006. Print.
NOT A LOGGING REQUIREMENT: Feel free to post pictures of your group at the area or the area itself - I love looking at the pictures.
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