Magma Deposits EarthCache
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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. Describe the area.
2. What evidence of magma deposits do you see? What is the reason for this?
3. What did geologists call the hardened magma that they found along Split Rock Creek?
4. On what building was this hardened magma was used to build a facade?
This Earthcache is located at Lien Park, along the Big Sioux River. Note the historical marker. Lien Park offers picnic tables and a dog off leash area. The park is well kept and has plenty of space for parking. Please observe the park hours and enjoy!
The outer layers of Earth are divided into lithosphere and asthenosphere. The lithosphere, which consists of the crust and upper mantle, is cooler and more rigid. Directly below the lithosphere in the upper mantle (between 62-124 miles below the surface of the Earth) is the asthenosphere, which is hotter than the lithosphere and flows more easily. The lithosphere (the rigid outer part of Earth, consisting of the crust and upper mantle) is broken up into what are called tectonic plates, which sit on the asthenosphere. 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).
Nearly 1.2 billion years ago, at a divergent boundary, molten rock called magma from deep in the Earth flowed up between two adjoining tectonic plates that were then located under present-day eastern Minnesota. Through a process called rifting, in which the rising magma causes the overlying lithosphere to move upward and stretch, some magma flowed underground into Minnehaha County, where it intruded into fractures in the overlying quartzite. While still below the surface of the Earth, the magma slowly cooled and hardened to form a dark-colored, coarse-grained rock.
Subsequent uplift of the Earth’s crust and erosion combined to expose and erode away most of the large body of solidified magma. Geologists first saw outcrops of the hardened magma north of Corson, South Dakota, along Split Rock Creek. In the early 1900s, the hardened magma was spotted in what is now Lien Park, and a quarry was opened.
Today, the quarry is gone and only scattered remnants of the hardened magma remain in the area.
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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