Indiana Dunes Rip Currents EarthCache

The dunes are adjacent to Lake Michigan and occupy only a narrow strip of land, a few miles wide at most. A few remnants of "older" sand dunes that extended as far south as Valparaiso (older because, as the lake shrank back in stages, new shoreline formed farther north) still exist as well. However, most of these older dunes and their adjoining ecosystems (such as wetlands and forests) have been leveled and drained for industrial or agricultural purposes.

Dunes are created when:

a plentiful supply of sand combines with,

wind blowing mostly from one direction,

and a natural trap causes the wind to drop the sand.

At Indiana Dunes, sand is lifted by winds blowing off the lake. A short distance inland plants, dunes, and hills slow the wind so that it drops its cargo, creating shoreline sand dunes. On windy days you can place a stone on the beach and watch the wind create a miniature dune behind it. With patience, you can lie down and watch yourself creating one.

The Indiana Dunes were created by these interactions and make this a prime area for rip currents.

Rip currents can occur along any coastline that features breaking waves. Scientific investigations of wave and current interactions along the coast have shown that rip currents are likely present on most beaches every day as a component of the complex pattern of nearshore circulation.

as waves travel from deep to shallow water, they eventually break near the shoreline. As waves break, they generate currents that flow in both the offshore (away from the coast) and alongshore directions. Currents flowing away from the coast are called rip currents. .

Basic Rip Current Mechanics .

• Waves break on the sand bars before they break in the channel area. • Wave breaking causes an increase in water level over the bars relative to the channel level. • A pressure gradient is created due to the higher water level over the bars. • This pressure gradient drives a current alongshore (the feeder current). • The longshore currents converge and turn seaward, flowing through the low area or channel between the sand bars. .

Although rip currents are not caused by tides, the water level (tide elevation) at the coast may have an impact on rip current speed and strength. Generally, rip current velocities increase as water levels (tide elevation) decrease. .

Rip current velocities also typically increase as wave heights increase. An increase in the height of incoming waves can result in sudden increases in water depth and rip current velocities. These sudden changes or pulses in water depth and current speed can catch bathers off-guard. Rip current pulsations are extremely dangerous to all swimmers! .

While average rip current velocities of 1 to 2 feet per second do not pose serious hazards to strong swimmers, rip currents may rapidly reach or exceed velocities of 3 feet per second. Also, rapid fluctuations or pulses in wave groups can quickly generate rip currents with extreme velocities that have been measured up to 8 feet per second – this is faster than an Olympic swimmer can sprint! If a swimmer is caught in a rip current, attempting to swim directly back to shore against the seaward flowing current can result in exhaustion and possible drowning.

Rip currents are usually narrow (~ 20 to100 feet in the alongshore direction), may extend hundreds of feet offshore, and generally span the entire water column. However, offshore, or outside the surf zone, they tend to be confined near the surface. .

Rip currents do not pull people under water – they pull people away from shore. Drowning deaths usually occur when people are unable to keep themselves afloat and swim back to shore. This may be due to fear, panic, exhaustion, a lack of swimming skills, or any combination of these factors. .

Some shorelines are characterized by permanent rip currents which may be found in a fixed location such as a break in a reef or other hard structure. Some rip currents are persistent, lasting for many days or months in one location. Rip currents may also migrate along a stretch of coastline. Rip currents may also be ephemeral, forming quickly and lingering for a few hours or days before dissipating and disappearing.

Rip currents are not rip tides. A specific type of current associated with tides may include both the ebb and flood tidal currents that are caused by egress and ingress of the tide through inlets and the mouths of estuaries, embayment's, and harbors. These currents may cause drowning deaths, but these tidal currents or tidal jets are separate and distinct phenomena from rip currents. Recommended terms for these phenomena include ebb jet , flood jet , or tidal jet . .

Undertow, an often misunderstood term, refers to the backwash of a wave along the sandy bottom. After a wave breaks and runs up the beach face, some of the water percolates into the sand, but much of it flows back down the beach face creating a thin layer of offshore-moving water with a relatively high velocity. This backwash can trip small children and carry them seaward. However, the next incoming wave causes higher landward velocities, pushing them back up on the beach. Undertow does not pull you under water or out to sea. .

HOW TO IDENTIFY RIP CURRENTS.

Look for any of these clues:.

• a channel of churning, choppy water • an area having a notable difference in water color • a line of foam, seaweed, or debris moving steadily seaward • a break in the incoming wave pattern .

None, one, or more of the above clues may indicate the presence of rip currents. Rip currents are often not readily or easily identifiable to the average beachgoer. For your safety, be aware of this major surf zone hazard. Polarized sunglasses make it easier to see the rip current clues provided above. .

HOW TO AVOID AND SURVIVE RIP CURRENTS.

Learn how to swim! .

• Never swim alone. • Be cautious at all times, especially when swimming at unguarded beaches. If in doubt, don’t go out! • Whenever possible, swim at a lifeguard protected beach. • Obey all instructions and orders from lifeguards. • If caught in a rip current, remain calm to conserve energy and think clearly. • Don’t fight the current. Swim out of the current in a direction following the shoreline. When out of the current, swim towards shore.

• If you are unable to swim out of the rip current, float or calmly tread water. When out of the current, swim towards shore. • If you are still unable to reach shore, draw attention to yourself: face the shore, wave your arms, and yell for help. • If you see someone in trouble, get help from a lifeguard. If a lifeguard is not available, have someone call 9-1-1 . Throw the rip current victim something that floats and yell instructions on how to escape. Remember, many people drown while trying to save someone else from a rip current..

To claim credit for this Earthcache you must do the following: .

1. Take a picture of you ( or your group) with GPS at posted coordinates.

2. What is the average velocity needed to form a rip current?

3. Name 2 ways to identify Rip Currents.

4. What is mistaken for a Rip Current?

5. This one is a bonus, What commonly happens at this general vicinity in the winter? Note signs state this as you enter the park.