Episode 207 S6-7
The Endless Night Ch 7
The Ogallala is a high planes aquifer system that spans from the north end of the Texas panhandle to southern South Dakota. Comprised of clay, silt, sand, and gravel, the spaces in between fill with groundwater. It was formed millions of years ago from streams that formed deep, course sedimentary rock. The underground water system created by the dirt that filled these streams used to receive water from the Rockies, but when it was cut off, the Ogallala became dependent upon rain and snowfall from above to fill it. This attrition is minimal accounting for about one inch a year.
The depth of the Ogallala beneath the ground is 500 feet down in some areas, but in others, it can be as close as 30 feet. Some areas of Nebraska boast a saturation level of 1000 feet, but most are much less. Nebraska's dominance of the Ogallala accounts for two-thirds of the total volume with Texas and Kansas tying for second with only ten percent. The storage capacity of the aquifer is comparable to the total volume of Lake Huron.
Since the 1940s the Ogallala Aquifer has become the most critical source of water in the high plains areas. It provides nearly all the drinking, irrigation, and industrial sources of water. One-fifth of the total US production of corn, wheat, cotton, and cattle rely upon the Ogallala's massive reservoir. However, since pumping in mass quantities began, there has been a one hundred foot decline in the level of the available water. This loss totals about 2.7 feet per year. There is lots of water stored in unsaturated zones that they attempt to exploit by blasting the area with air to push the water into usable spaces.
The Ogallala is facing some significant threats. Not only is it being drained at rapid rates but chemical contaminants from the farming activities above leach down to the reservoir below. Current amounts are not notable by the FDA, but as the water decreases and the contamination continues, this ratio is sure to change.
Farmers are taking an active role in the conservation of the Ogallala. New technology allows them to apply moisture sensors to the soil to avoid over-watering. They are switching to pivot sprinklers that conserve more water than the center point sprinklers. They are testing dry earth planting methods and planting the plant further apart to keep the soil moister.
For the Ogallala to collapse, as told in the Changing Earth Series, it would have to be a significant sinkhole event. Sinkholes happen in areas with no external drainage systems for the water. The collapse is usually caused by "karst" terrain. This soil consist of dissolvable rocks below the surface. Susceptible to erosion, the rainwater can destroy them, and the weight above causes a collapse.
There are a few types of natural sinkholes. When a solid mixes with a solvent resulting in a solution, it creates a dissolution sinkhole. The collapse happens when the rock erodes. A cover-collapse sinkhole is like a giant cavity in your tooth. The material under the ground decays, and a thin layer of soil remains until it collapses under the weight of the above-ground activity. Cover-subsidence sinkholes are when holes in limestone allow sand to enter and fill the drainage areas. This build-up of water results in a pond forming.
Then there are human-made sinkholes. Old mines, leaky pipes, sewers, and water lines form these sinkholes. Basically, anything that is built underground or runs a liquid underground. The industrial and runoff ponds can also put so much weight on top of the earth that there will be a collapse. The final way a sinkhole can form or subsidence (ground level collapse) can happen is through the use of groundwater pumping. The pumping disrupts the balance of dirt to water underground and reduces the groundwater level. This weakening can leave the ground above very susceptible to collapse.
Karst soil seems to be the key to sinkhole events, and the southern end of the Ogallala is rich with it. Texas is extremely sinkhole-prone thanks to the land. Oklahoma and east Colorado also show a fair amount of karst soil. The other ground that is susceptible is any soil composed of evaporative rock. There is a large vein of this type of soil that runs directly up the central region of the United States, directly under the Ogallala.
A potential trigger for such a collapse event might be an earthquake. The central part of the United States experienced very few earthquakes until the introduction of oil and natural gas pumping. These industries dispose of wastewater by pumping it back into the earth, causing induced earthquakes. These induced earthquakes are on the rise. Since 2009 the average M3 earthquakes jumped to 362 per year, and in 2015 there were 1010 M3 or higher earthquakes in the region. Oklahoma is a major point of concern for this activity.
Everything in life requires moderation. To maintain the stability of the heartland, education about the Ogallala is imperative, so the potential consequences of our actions are understood before disaster strikes. Technology, conservation, and general awareness of the potential for catastrophe are paramount for the longevity of the Ogallala Aquifer.
Ogallala Saturation Thickness
Ogallala Map of Water Usage
Karst in the United States
Induced Earthquakes in the Central US
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