What are tides?
A tide is the alternating advance and retreat of seawater along a shoreline. When the water reaches its greatest extent along the shoreline, it is said to be at high tide. When the tide recedes to its greatest extent, it is low tide. Tides can occur in several freshwater rivers and lakes, as well as seas and oceans. High and low tides are caused by the moon’s gravitational pull on the Earth and the Earth’s rotational force. The side of the Earth nearest to the Moon will experience the strongest pull, causing oceans to rise and high tides to occur. The rotating force of the Earth is greater than the gravitational force of the Moon on the side facing away from it. Because the rotational force causes water to build up as it tries to resist the force, high tides arise on this side as well. The ocean recedes elsewhere on Earth, resulting in low tides. The Sun’s gravitational attraction also plays a minor influence in the production of tides. Tides circulate the Earth as bulges in the ocean.
Types of Tides:
Semidiurnal and mixed semidiurnal tides are the most common type. It consists of 2 high tides and 2 low tides in one lunar day (approximately 25 hours). The difference in height between the high tide and the low tide is called the tidal range.
Diurnal tides consist of just 1 high tide and 1 low tide on each lunar day.
What are ripple marks?
Ripple marks are ridges of sediment that form in response to wind blowing along a layer of sediment. They are formed perpendicular to the wind direction and each ridge is roughly equidistant from the ripple mark on either side. The troughs and ridges of fossilized ripple mark in sandstone and siltstones are hardened versions of the short-lived ripples in the loose sand of a modern-day stream, lake, sea, or sand dune. Ripples may be made by water or, in sand dunes, by wind. The symmetry of water-current ripple marks indicate whether they were formed by gentle waves or faster water currents.
Types of ripples:
Straight ripples point in the same direction. They are constructed by unidirectional flow of the current.
Sinuous ripples are curve-shaped. They show a pattern of curving up and down as shown in the picture. Sinuous ripples are formed by dipping at an angle to the flow of water.
Linguoid ripples generate an angle to the flow as well as downstream. Linguoid ripples have a random shape as seen below.
REMINDER:
**You are not obligated to find this geocache. Remember to exercise caution entering and wading in the water. Enter the water at your own risk.**
Logging Tasks:
- Based on the information/images provided in the description and your observations at the GZ, what type of tides does Ocean City experience?
- Use https://tidesandcurrents.noaa.gov/noaatidepredictions.html?id=8534836 to view the tide predictions for Atlantic County, NJ. Did you visit near high or low tide? Observe how this affects the surf at the GZ.
- Which of the three types of ripple marks are observed in the sand at the GZ? Explain your rationale.
- Estimate the distance between the trough and ridges of the ripple marks.
**Depending on the day, weather conditions, and tidal levels you may need to wade into the water to see the ripples.**
- As of June 2019, earthcaches now contain required photo logging tasks. Please provide a photo of yourself, your GPSr, or a personal item that proves that you have visited this site. You can put this in your log.
Sources:
https://www.geologypage.com/2017/11/ripple-marks.html#:~:text=November%209%2C%202017-,Ripple%20Marks,along%20a%20layer%20of%20sediment.
https://geology.com/rocks/sandstone.shtml#:~:text=Sandstone%20is%20a%20sedimentary%20rock,spaces%20between%20the%20sand%20grains.
https://www.thoughtco.com/tidal-pool-overview-2291685
https://www.americanoceans.org/facts/information-guide-high-low-tide/
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