Armored Mud Balls and Mud Cracks in Southern Utah

September 27, 2021


Photographer: Tom McGuire

Summary Author: Tom McGuire; Cadan Cummings

The picture above features armored mud balls and soil cracking taken near the trailhead of the Wire Pass in Kane County, Utah. Armored mud balls are spherical soil formations composed of a mixture of silt, clay, sand, and gravel that form in stream beds or previously flooded areas. The diameter of mud balls usually ranges between 2 to 4 inches (5 to 10 cm), but it largely depends on the soil particles and gravel present. The size of the particles in a stream bed is directly related to the speed of the water. This means that when stream water slows down, larger particles like gravel and sand are deposited first, while smaller soil particles such as silt and clay can stay suspended in the water until the water is mostly stagnant. Sediments can be mud where flood water becomes stagnant, or pebbles deposited in a moderate current. As mud dries, it hardens and forms tessellated chunks caused by shrinking during desiccation.  

Cracked pieces of soil may be dislodged by wind or water, while the mud is still wet below the surface. The pieces become round as they are pushed along the surface. Rolling balls of sticky mud can pick up pebbles that “armor” them. These armored mud balls were found below the Buckskin Wash trailhead on the Utah-Arizona border. Mud balls can also be geologically preserved given the correct environmental conditions. Such examples include fossilized Triassic mud balls collected by Professor Richard Little, which are displayed in the Greenfield Community College Rock Park north of Amherst, Massachusetts.

Photo Details: Olympus E-510: 42 mm, f/9, 1/250 second exposure, ISO-100

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