A spring is releasing its clear water down a canyon wall. The iron in the water then is being used by bacteria to support its life. The orange color is a by-product of the bacteria’s digestion. Photo by Robert Dryja
By ROBERT DRYJA
We have reviewed in prior articles the geologic characteristics of Upper Pueblo Canyon and the impact of the Cerro Grande Forest fire on the landscape. Flash floods have a dramatic impact on the canyon but there are subtle impacts as well.
Upper Pueblo Canyon descends 1,300-foot in elevation along its length. Surface water flows quickly but sub-surface water moves differently. It soaks downward into the porous soil and also moves at an angle, following the downward slope.
The velocity of subsurface water can vary widely. One foot per day is a high rate while one foot per year is a low rate. This means sub-surface water moving along the canyon could take approximately 43 years at the high rate or 15,840 years at the low rate to traverse the three-mile length.
Sub-surface water may emerge from springs along the way. Two springs can be seen in Upper Pueblo Canyon. Both springs are a trickle of water that falls a short distance to the canyon floor. The water accumulates in small pools before being absorbed again into the ground.
The two springs could not be more different in appearance from one another. The water from one spring is completely clear as it emerges, falling a few inches to a pond. The pond water is clear and shaded by trees.
The appearance of the second spring is very different. Clear water flows down the side of a vertical rock wall for about four feet before entering a small pond. The canyon wall is a bright orange where the water flows over it. The water in the pond also is a murky orange where the falling water first enters. What is making the orange coloration?
There are dry areas next to the wet area. These have a light orange color directly on the rock. This suggests that that the water is dissolving some kind of mineral from the rock and exposing it when it dries. However, a thick slimy column can be seen in the wet area. An iron oxidizing bacterium is using iron dissolved in the water to obtain energy. An orange slime is created in the process.
What looks like dried orange rock on the sides of the wet column is actually a surface covering of dried slime. Some of the slime is being washed into the pond by the falling water. This is creating the orange color adjacent to where the water first enters the pond.
The presence of butterflies sipping the spring water indicates it is acceptable for their needs, just as the iron-oxidizing bacteria are using it for its needs. The butterflies sip clear water only where the bacterial slime is not present. Look at the color of the cliff side when driving along the main hill road to Los Alamos. Iron is present in this cliff. Its color is similar to the color of the slime in the water column created by the spring. This impressive vertical cliff then may remind you of the lives of bacteria and butterflies.
A butterfly sips the spring water that is flowing nearby but is not a part of the orange slime. Photo by Robert Dryja