Updated July 8, 2019 to make the answers clear even if there is no water due to periodic Texas droughts. The final is the same.
Pioneer Plaza Waterfall is an educational two stage multicache located at the edge of downtown.
Pioneer Plaza is the largest public open space in the Dallas central business district. It is located in between the Dallas Convention Center and the Pioneer Park Cemetery. Within the park itself there is a shallow flowing stream, a man-made limestone cliff with an artificial ridge, and some iconic western sculptures. On the side of this cliff, there is a waterfall (which is the educational focus of this geocache).
Some definitions:
- Waterfall - a steep fall of water, as of a stream, from a height; or a cascade.
- Plunge pool- a deep depression in a stream bed at the base of a waterfall.
- Erosion- a condition in nature in which something is worn away, or a landscape is formed by wearing away gradually.
- Bedrock - the solid rock that lies beneath the soil and other loose material on the Earth's surface.
How waterfalls are formed:
Waterfalls normally only occur in areas with rich geology and varying rock layers. Waterfalls are formed when the water travels over different layers and types of rock. Each of these rock layers and types vary in hardness and therefore have different rates of erosion. Knowing that water is an erosive agent, the water erodes the rock and ground at different rates. Basically, a river or stream flows over he hard bedrock and it flows over other soft rock. (Figure 1) The harder rock (possible bedrock) is more resistant to erosion, while the softer rock experiences erosion more rapidly.
As the water flows over the softer rock, it is able to erode it at a faster rate. This uneven erosion creates a step in the riverbed. (Figure 2) Over time, this step is further cut into since it is softer rock. This of course is when the water tumbles over the hard rock layer and is the start of the waterfall formation. The step accelerates erosion due to hydraulic action in which, due to the increase slope of the riverbed, gravity pulls the water more vertically down instead of horizontally down. This increases the speed of the water as well as the force from it falling. When people see this, they typically call it a cascades or rapids.
It continues cutting away the soft material beneath the harder bedrock while making the edge steeper between the two rock layers. The edge between the bedrock and the soft rock eventually steepens until it is nearly vertical or completely vertical. Then you have a waterfall! (Figure 3)
At this point, the tumbling water is continuing to cut into the softer rock beneath the harder rock. The waterfall gets taller and it deepens the plunge pool. As soft rock in the plunge pool erodes, the soft rock next to it is undercut and erodes as well. This creates a pocket behind the plunging water. As the undercutting continues, eventually there is not enough support under the harder rock that is overhanging at the top of the waterfall. (Figure 4) It becomes unstable and collapses into the plunge pool. (Figure 5) This results in the waterfall retreating further up stream to the remaining edge of the hard rock layer. The process of erosion continues until the entire bedrock layer of hard rock has collapsed. At that point the waterfall will look like a normal stream or small set of rapids. (The collapsed rock may lead to a secondary waterfall formation and the process continues. Eventually though the collapsed rock will erode due to the waterfall pouring directly on it).
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This specific Waterfall:
Most of the Dallas area is covered in Black-Heiden soil, which is a rather soft clayey soil. The cliff of this waterfall is made from limestone, which is a harder type of stone. If this were a natural waterfall, the water would flow over the limestone and then over the clay soil and any dirt. It would erode the soil with little or no disturbance to the limestone. (In the case of this waterfall, it appears Dallas just skipped the clay and put in the limestone and cement to create the ridge).
Information has been extracted and adapted from the following sources:
Geocache Details
Virtual Stage 1: Go to the coordinates and determine the answers to the questions below.
DO NOT include them in your log.
1. What is the estimated height of the waterfall?(top to plungepool)
Less then 5 feet tall W 96° 48.300
About 10 feet W 96° 48.011
More then 30 feet tall W 96° 48.959
2. When facing the waterfall, which direction does the water flow from the plunge pool?
Mostly North N 32° 46.560
Mostly South N 32° 46.002
Mostly East N 32° 46.731
Mostly West N 32° 46.630
Stage 2 is the final! Take your answers from above and go find the geocache. It is at the end even though buildings may cause your gps to jump around.
***Note: this area can be busy at different times. Be careful of traffic and muggles.
You must sign the log to claim the find so bring a pen. No exceptions and no excuses. Blank logs may be deleted without notice. Avoid the use of acronym only logs. Photos are highly encouraged but not required. (Please don’t post pictures that give away all the answers.)
Congrats to kennedkr and ARKS for both being the Co-FTF.