Sandbars come in many different types and sizes, made up of many different materials.
River Sandbars
A river sandbar is formed differently than its coastal counterpart. River water carries silt, sand and clay in its narrow channel, but as it flows around curves the water on one side slows down and the other speeds up. On the one side this difference in speed allows the heavier particulates in the water to fall out creating the bar or shoal.
Sand
In a most basic sense, the sand on our beaches comes from the erosion of the land. Sand consists of rocks, crystals, shells and skeletal remains of organisms, eroded over time by water, wind, and ice. The composition differs greatly from different parts of the world. In Hawaii, the black sands are mostly made up of volcanic ash, while in New Mexico the white sands are composed mainly of gypsum. Many beaches contain magnetite which is chemically resistant, durable, and it resists abrasion. It can be transported by the wind and water.
In our area the beaches rely on sand transported mostly from the mountains and lands by the rivers and from eroding cliffs near the shoreline. The particles are suspended in the river until they are deposited by the currents along the beach. This sandbank is a linear landform that is typically composed of sand, silt, or small pebbles. Sandbanks tend to build where a river current promotes depositing of the granular material, which often happens where the current slows down due to bends in the river.
Sand varies in size from silt to gravel. In the United States it is divided into 5 sub-categories: very fine, fine, medium, coarse, and very coarse. The composition of sand is highly variable since it depends on local rock sources and conditions. Sand found near its source will be different sizes (not well sorted) while sand found far from its origin will be about all the same size (well sorted).
This earthcache will bring you to a sand beach along the Iowa River. To demonstrate the educational value of this cache, please answer the following questions. Submit the answers to these questions to the cache owner: Do not post your answers with your log. Photos are optional, but appreciated and encouraged.
Pick up a handful of sand and tell us what you see and feel.
a) How would you categorize the sand according to one of the 5 above categories?
b) What size particles do you see?
c) Do you think the sand is well sorted or not?
d) Do you feel the sand came from nearby or far away?
e) On which side of the river bend does the water move slower and deposit the sand?