The Falls 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. How many separate falls can be seen at this location?
2. Estimate the height of the main waterfall.
3. Rate the waterfall on a scale of 1-10 based on the volume of water present.
4. For the main waterfall, identify its type.
This earthcache is located at Falls Park in Sioux Falls. There are several sidewalks that will take you to different vantage points around the falls. These paths are also dotted with informational signs detailing the history of the area. An observation tower, a souvenir shop, and a cafe are also located in the park. Enjoy!
Waterfalls are formed through the process of erosion or the wearing down of the Earth’s surface. While wind and glacial ice, two natural elements, are responsible for erosion in some areas, water is the most common and most powerful elements that causes erosion.
Waterfalls start out as small rapids and form where a band of hard or resistant rock lies next to soft rock. As the river passes over the hard rock, the soft rock below it is eroded more quickly than the hard rock. This creates a “step” by elevating the hard rock above the stream bed below. This “step” in the river flow continues to develop over time as the river continues to flow over the hard rock as a vertical drop. This drop gets steeper as the river continues to erode the soft rock beneath it through processes such as abrasion and hydraulic action.
Abrasion is a mechanical scraping of a rock’s surface by friction between rocks and moving particles during their transport by wind, glaciers, waves, gravity, or running water. The abrasion in this case would be caused by the moving river. The friction of the rocks scraping against each other dislodges loose and weak debris from the side of the rock - slowly chipping away at it.
Hydraulic action is a form of erosion caused by the force of moving water currents rushing into a crack in the surface of a rock. As the water rushes in, it compresses the air in the crack; as it retreats from the rock, the highly pressurized air is suddenly released with an explosive force. This process gradually widens the crack, which, in turn, increases the amount of compressed air inside the rock, which increases the explosive force of its release. This force is strong enough to chip away the surface of the rock over time.
While erosion causes the fall of the water to steepen, it also causes a plunge pool to form at the base of the waterfall. A plunge pool is a pond that is small in diameter, but deep. Water going over the falls carries with it sand and pebbles. As these pebbles fall, they end up in the swirling waters directly below the falls and move around in a circle or vertical whirlpool until further carried away. While the sediments are caught in this whirlpool, they scour the riverbed, slowly eroding and deepening it. Further abrasion and hydraulic action also cause the plunge pool to enlarge and deepen.
Eventually, all of this erosion gradually undercuts the hard rock (the soft rock below it is eroded) and the hard rock becomes unsupported and collapses. The rocks that fall into the plunge pool will continue to enlarge it by abrasion as they are swirled around. A steep sided valley called a gorge is left behind, and the erosion process continues as the waterfall gradually retreats upstream.
Waterfalls are rated on a scale on 1-10 based on the average volume of water present on the fall. Class 10 waterfalls are the most powerful and include Niagara Falls. Class 1 waterfalls are the weakest because they have the lowest volume of water on the fall. Waterfalls are also classified into ten different categories.
- block: water descends from a relatively wide stream or river
- cascade: water descends a series of rock steps
- cataract: a large, powerful waterfall
- fanny: water spreads horizontally as it descends while remaining in contact with bedrock
- horsetail: descending water maintains some contact with bedrock
- plunge: water descends vertically, losing contact with the bedrock surface
- punchbowl: water descends in a constricted form and then spreads out in a wider pool
- segmented: distinctly separate flows of water form as it descends
- tiered: water drops in a series of distinct steps or falls
- multi-step: a series of waterfalls one after another of roughly the same size - each with its own sunken plunge pool
Here at Falls Park, the Big Sioux River has been working for many years to create the waterfalls you see. The hard rock the water passes over is quartzite.
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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