High School
Teacher's Guide
to Craters of the Moon
Chapter Five:
Water Quality
Chapter Five:
Water Quality
Water is extremely scarce at Craters of the Moon. Little Cottonwood and Leech Creeks, which flow from springs in the foothills of the Pioneer Mountains, are the only two streams in the Monument. They disappear below ground at the edge of the lava flows. Throughout the rest of the Monument, water exists only in scattered water holes and ice caves.
Water holes appear to form when water percolating downward meets an unusually non-porous layer of lava, where the water may collect into a pool. If the temperature in these locations is below freezing, the water turns to ice. Ice, too, forms an impermeable layer that traps water above it. These water holes provide oases for animals living in the volcanic desert. Early explorers of the lava fields located water by watching for concentrations of birds circling in the air above water holes.
Ironically, deep below the parched surface of the lava beds lies an enormous reservoir of fresh water, the "Snake River Plain aquifer." The Snake River Plain aquifer is a huge underground body of water covering 10,000 square miles, stretching from the town of Hagerman upstream to near St. Anthony. The aquifer is made up of water which is stored in a series of lava flows erupted over the past 15 million years. The lava flows are separated by layers of broken rock and cinders as well as sand, gravel, and clay which mark the location of ancient lakes and rivers. In addition, the lava is cracked, leaving large spaces through which water can flow. These rock layers act like a giant sponge, with a storage capacity of 200 million acre feet!
Farmers depend on the aquifer to irrigate over one million acres annually. Most farms also depend on wells for domestic and stock water. In addition, over 41 communities serving 127,000 people utilize the aquifer for municipal water supplies, either from wells or springs.
The aquifer lies approximately 1,000 feet below the surface and flows slowly, following the gradual slope of the Snake River Plain. Streams entering the lava plain, rain, and snow melt all disappear into the porous rock. The water then makes its slow journey southwestward, eventually cascading from the canyon walls into the Snake River at Thousand Springs.
In 1992, researchers began an Aquatic Resources Assessment at Craters of the Moon. The study collected baseline data on water and ice in the Monument. It also documented the physical condition of the streams and chemical content of the water in streams, water holes, ice caves, and wells. In addition, researchers examined the invertebrate animal life of streams, and they reviewed historical documents for any trends in water quantity. This study established what existing conditions are, and created guidelines for ongoing monitoring to detect any significant changes.
The study indicates that minerals may be leaching from the mine tailings at the abandoned Martin Mine into the water of Little Cottonwood Creek. Samples from the spring box on Little Cottonwood Creek, upstream from this area, demonstrate that the springs come from a surface source and not from groundwater as previously thought. Sampling of water in several ice caves showed that the water may come from atmospheric condensation and not from percolation of ground water, as had been previously assumed. Finally, the pH and temperature in both creeks tested was normal.
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