INDIANA DUNES
RIP CURRENTS
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.
Only during winter months.