The Secret of the Tides - Eva Varga

I grew up in Bandon, Oregon and though we now live in the valley of northern California, we travel home as often as possible.  While we go primarily to see family, the ocean pulls us to her just as compellingly.  We have enjoyed exploring the tide pools, investigating the unique estuarine habitats, and tasted freshly caught Dungeness crab many times in the past.  Recently, however, we spent some time taking a closer look and discovering the secret of the tides.

As pictured in the the photo collage above, we visited a beach access area at both low tide (6:59 a.m. @ -1.9′) and high tide (6:56 p.m. @ 1.5′).  I specifically selected this area because on low tide, we had access to tide pools.  Shortly after I took the photo, we walked down the stairway and spent time investigating the marine invertebrates.  While we marveled at the sea stars and innumerable sea anemones, I began to pose questions about the animals we observed and about the wave evidence on the shoreline.  We noted specifically where we found each species and shared our hypothesis for how these organisms could survive in such a dramatically changing environment. I’ll share our discoveries soon – the kids are still working on their nature journals.

Create a Tide Graph

One of the most useful activities we undertook this past week was to create a tide graph and then use the newspaper to also plot the corresponding moon phases.  To create a tide graph yourself, use a tide chart and select a specific month; you can access tidal data from NOAA.  Use a piece of graph paper to  graph the highest high tide and the lowest low tide for each day (recall there are typically two high tides and two low tides each day).  Use a different colored pencil for each tide type.  The day of the month should be on the x-axis and the height of the tide on the y-axis.  Tides can be negative, so be sure to include negative numbers on your y-axis.

Lastly, find a moon phase calendar for the selected month (or look up the moon phase in your local newspaper).  Sketch the four major moon phases (new moon, 1st quarter moon, full moon, and 3rd quarter moon) under the corresponding calendar date and label them accordingly.  After completing the graph, answer the questions listed below.

• Is there a relationship between the phase of the moon and the tides?  Explain what you observed based upon your graph.
• What are spring tides? Based upon your data, around what phase(s) of the moon do spring tides occur?  How do you know this?
• What are neap tides? Based upon your data, around what phase(s) of the moon do neap tides occur?  How do you know this?

Take it Further

If you have enjoyed this activity and would like to explore related lessons and inquiry activities, check out Estuary Ecology, a fourteen lesson hands-on life science curriculum unit study that focuses upon estuaries and salt water marshes.

** Please note that graphs will vary depending upon the selected location and time of year.  A great extension activity is to create tide graphs for distinctly different locations (Newport, Oregon and Cape Code, Massachusetts, for example) and/or different seasons.

Submitted to the Outdoor Hour Challenge Blog Carnival at Handbook of Nature Study.