The posted coordinates will take you to a shoulder pull-off next to the Fox River, on IL Route 25. This is a public roadway. You can park your vehicle at the posted coordinates, or you can utilize the bike trail and either ride a bike or walk to the posted coordinates.
The Fox River is a tributary river that flows 202 miles from Southeastern Wisconsin to Ottawa, Illinois where it enters the Illinois River.
Throughout much of the Fox River's journey, there are several islands that have formed. Some are very tiny while others are quite substantial. The islands that form inside a river body are called riverine islands. They are also sometimes referred to as eyots or aits.
While standing at the posted coordinates, there are a few islands in view. But why are these islands here and how were they formed? Let's discuss.
What exactly is an riverine island? Definition: Any exposed land surrounded by river water.
The river islands you see in the water in front of you were most likely created over the course of several years. There are 2 main processes through which river islands are formed: 1) Deposition of sediment and 2) Anabranches.
DEPOSITION OF SEDIMENTARY MATERIALS
The deposition of sediment is the process in which a solid material (sand, gravel, soil, etc) is transported from its site of orgination (by air, water, gravity, or ice) to a field or low landscape position. Rivers naturally flow from higher elevation to lower elevation and carry sedimentary materials as they flow. Deposition occurs most frequently when the flow rate of rivers are low. This allows sediment to settle to the riverbed because there is less force pushing/carrying the sediment down the river. When a river widens, the flow rate of the water also slows down. Many of the islands on the Fox can be found at the widest points of the river, and near riverbends, where the flow rate is the slowest.
One unique factor of the Fox River is that it has 15 dams spread across its 202-mile journey. These dams drastically slow down the flow rate of the river. Looking at an aerial map of the Fox, one can see the majority of the islands are down-stream, and in close proximity, of the dams. Again, this is due to the fact that deposition occurs where the water flow is weakened or slowed.
Sediment deposition can create a natural force of resistance in the water flow. This resistance can cause more sedimentary material to be deposited in the same area over a period of time...thus resulting in the formation of small river islands. Over the course of time, these islands can grow larger, and even "move", through further depostion of sediment along the banks of the island. Islands can "move" though the combined means of both erosion and deposition. As water flow erodes the back end of the island erodes, the sediment can be deposited at the front end of the island, thus causing the island to "move" downstream ever so slightly.
Another interesting fact about the Fox: the area surrounding the Fox River (known as the Fox River Valley) is rich in limestone. In fact, 9 limestone quarries were once located 10 miles upstream on the Fox River, in the city of Batavia. The quarries operated from the 1840s through the 1920s. Downstream of Batavia, specifically, limestone deposition makes up much of the Fox River's riverbed. When the river level is low, limestone gravel is clearly evident in the riverbed that you see in front of you at ground zero.
ANABRANCHES
Another cause of eyots are anabranches. An anabranch is an arm of a river that temporarily diverts from the main body or channel of the watercourse but rejoins the main body at a later point downstream. Anabranches use the process of erosion to cut away at the soil and create a new arm, or branch, of the river. Small, short anabranches form islands like the ones you see in front of you, at ground zero. Larger, longer anabranches are responsbile for the creation of giant islands, such as Stolp Island, located just 3 miles upstream, on the Fox River. Stolp Island is a 19-acre island which is home to several businesses, restaurants and retail shops.
Some anabranches are seasonal or temporary and occur only during periods of heavy rainfall and flooding. Water may leave a river or stream during highwater and find its way back when the waterlevel receeds. The Darling River anabranch is New South Wales, Australia is an example of a seasonal anabranch. It is 287 miles long but only flows during wetter months of the year.
Different Types of Riverine Islands
There are a few different catagories of riverine islands:
- Seasonal Island: Seasonal islands are temporary islands that form mainly during the rainy season. These islands are no more when summer comes because the water in these rivers usually dries down in the summer.
- Permanent Island: We all know that some rivers always flow persistently or are evergreen in all seasons. The islets of these types of rivers are permanent and some of them are habitable. The inhabitants of many small islands live there and do everything possible there, such as fishing, farming, and several other works.
- Flooded Island: Some islands in the river only forms when there is a flood. When the flood water level drops, these islands are no longer islands.
- Single River island: Single river islands create a solid foundation in the middle of the river. Water flows around the islands. These types of islets are formed at a sharp bend of the river.
- Parallel River Island: When two parallel rivers flow together and a solid place naturally forms between these rivers, they are called parallel river islands. There are very few naturally formed parallel river islands available. The maximum available river islands are single river islands.
- Coastline River Island: Most of the rivers end up on oceanic coastlines. River islets that naturally form the coastline on the other side are called coastal river islands.
- Habitable river islands: Habitable river islands are islands with comfortable inhabitants. There are thousands of islands available where people can live with basic needs. But the life of the people living here is very difficult. It’s really hard to live on small islands in the middle of the river like this.
IN ORDER TO LOG THIS EARTHCACHE, YOU MUST PERFORM THE FOLLOWING ACTIVITIES:
1) Standing at the posted coordinates, take a photo of yourself, your group, or a personal item with the Fox River island(s) clearly visible in the background and attach it to your log. (A sign with your caching name or your GPS unit will suffice as an identifiable personal item.)
AND
2) Email me the answers to the following questions. Do NOT post your answers in your log!
a) What are the 2 processes that are mainly responsible for the creation of river islands / eyots?
b) Which of the above listed processes do you feel was responsible for the creation of the river islands you see in front of you?
c) Do you see any evidence of sedimentary material deposition? If so, what type of material do you see?
YOU MUST PROVE THAT YOU ACTUALLY VISITED THIS EARTHCACHE!
LOGS WITHOUT PHOTOS WILL BE DELETED!
YOU MAY OPT TO EMAIL ME YOUR PHOTO IF YOU DO NOT WANT TO POST IT IN YOUR LOG.
Sources:
https://en.wikipedia.org/wiki/River_island
https://en.wikipedia.org/wiki/Deposition_(geology)
https://en.wikipedia.org/wiki/Anabranch
https://www.shawlocal.com/2016/05/05/park-district-dish-batavia-is-swimming-in-history/ag43jqh
http://www.encyclopedia.chicagohistory.org/pages/481.html