Know before you go: This EarthCache is located on the beach of Indiana Dunes National Park. According to NPS guidelines, “prohibited activities on the beach include:
- The removal of natural items such as rocks, shells, and fossils.
- Wood and charcoal fires on the beach. West Beach and Lake View Beach do have dedicated grills in the picnic areas.
- Glass containers on all beaches.
- Pet rules differ for each beach area. Please visit the Pet Information Page.
- Launching, landing, or operating any unmanned aircraft (e.g. model airplanes, quadcopters, drones) on lands and waters administered by the National Park Service within the boundaries of Indiana Dunes National Park except as approved in writing by the superintendent.”
Please visit https://www.nps.gov/indu/planyourvisit/beach-safety.htm for more information.
Safety in the Water: At Indiana Dunes National Park and in other beaches on Lake Michigan, rip currents can be found. The NPS outlines a rip current to be “a strong, localized, and narrow current of water which moves away from the shore, cutting through the lines of breaking waves like a river running out to deeper waters. A rip current is strongest and fastest nearest the surface of the water and can pull swimmers out from the shore at speeds up to eight feet per second for hundreds of yards.” If caught in a rip current, it is recommended to swim away from the direction of the current, as shown in the below graphic:
For more information about beach safety, please visit https://www.nps.gov/indu/planyourvisit/beach-safety.htm and https://glsrp.org/water-safety/.
**A local EarthCache in the park also highlights the geology of how rip currents form found here.**
The Geological History of Indiana Dunes:
Between 70,000 and 10,000 years ago, much of the Midwestern United States was covered in glaciers, known as the Wisconsian Glaciation. About 13,000 years ago, these glaciers started to retreat into Canada, revealing river systems, the Great Lakes, and glacial sediment known as moraine. Moraine can range from the tiny clay particles found in soil to large boulders. On the beach, most sand is composed of granules of quartz and some magnetite moraine. At Indiana Dunes National Park, most dune formations are created from sand and gravel moraine from these glaciers. Two main processes on the lakeshore help aid the dune formation process: wave action (swash) and longshore drift.
Lakeshore Process #1: Swash
What is Swash (Wave Action)?
Swash refers to the turbulent layer of water that rushes onto the lakeshore following the breaking of an incoming wave. This swash action can transport beach materials back and forth along the shoreline, leading to sediment exchange in the cross-shore direction. The duration of swash motion varies, ranging from seconds to minutes, contingent upon the beach type. Flatter beaches generally experience more pronounced swash. The swash motion is instrumental in shaping morphological features within the swash zone, and it serves as an instantaneous process in broader coastal morphodynamics.
The swash process encompasses two distinct phases: uprush, characterized by onshore flow, and backwash, involving offshore flow. Typically, uprush exhibits higher velocity but shorter duration compared to backwash. Onshore velocities peak at the onset of uprush and subsequently decrease, while offshore velocities rise towards the conclusion of the backwash. The prevailing wind influences the direction of the uprush, whereas the backwash consistently moves perpendicular to the coastline.
Constructive vs. Destructive Waves:
Destructive waves are a natural cause of erosion of beaches. These high-energy waves are more potent in stormy conditions. When waves have stronger backwashes than uprushes, they pull material away from the shoreline and into the sea, resulting in erosion.
Constructive waves are a natural way of depositing sand on beaches. These waves are much less intense, allowing sand, clay, rocks, and debris to build up on the lakeshore. The main characteristic of constructive waves is that they have stronger uprushes than backwashes. In many places worldwide, constructive waves have led to the creation of beaches and dune systems.
Lakeshore Process #2: Longshore Drift
Longshore drift is the movement of sand across a shoreline. The processes of uprush and backwash occur at an angle (see the picture below) as bring sand onto and off the beach. As a result, sand gets transported along the beach. These “rivers of sand” occur on both ocean coasts and lakeshores. At Indiana Dunes National Park, most of the sand on West Beach comes from northeastern lakeshore beaches. A significant powerplant facility is situated to the northeast of the beach at the GZ. The built-up region along the lakeshore is probably hindering the movement of sand beyond it. This obstruction of longshore drift may result in beach starvation and heightened erosion of the lakeshore and dunes in the coming years.
We recommend you visit brcross95’s EarthCache to learn more about Indiana Dune’s beach starvation here.
Logging Tasks:
- What is the duration (in seconds) between the uprush and backwash?
- Use the website https://seatemperature.info/indiana-dunes-tides.html for a tide forecast. Did you visit near high or low tide? How did this affect the amount of swash?
- Would you classify the waves at the GZ to be constructive or destructive? How do they impact the process of dune formation at Indiana Dunes National Park?
- How do anthropogenic (human-caused) effects impact the process of longshore drift and dune formation?
- As of June 2019, EarthCaches may have required photo logging tasks. Please provide a photo of yourself, your GPSr, or a personal item that proves that you have visited this site. Please post this in your log.
Sources:
https://www.southshorecva.com/things-to-do/indiana-dunes/history/#:~:text=History%20of%20the%20Indiana%20Dunes,make%20up%20the%20Indiana%20Dunes
https://www.gsi.ie/en-ie/geoscience-topics/natural-hazards/Pages/Coastal-Erosion.aspx#:~:text=Destructive%20waves%20have%20stronger%20backwashes,the%20sea%20resulting%20in%20erosion.&text=Constructive%20waves%2C%20on%20the%20other,of%20material%20on%20the%20shoreline
https://www.usgs.gov/geology-and-ecology-of-national-parks/geology-indiana-dunes-national-park#:~:text=Dunes%20need%20three%20things%20in,Michigan%20meet%20all%20these%20criteria
https://www.indianadunes.com/explore-the-dunes/plan-your-visit/dunes-101/geographic-regions/the-dunes/
https://www.naturalnavigator.com/news/2018/12/what-is-swash/
https://itssedimentary.com/2014/09/28/geology-of-the-indiana-dunes-located-in/
https://www.internetgeography.net/topics/what-is-longshore-drift/
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