Wednesday, November 2, 2011

Down on the beach

Breaking waves on a sandy beach
I took a group of students down to a local beach last week – it turned out to be the only day that week that poured rain (I often have that kind of luck). As the students were doing their work, I walked up and down the beach to check on them. Since I was dressed for the rain I didn't mind the weather, in fact I found it pleasant to be away from my computer for a few hours. In addition to my rain jacket, I wore my rubber boots so I could walk through the shallowest waves and feel their strength tugging at my ankles. Okay, the real reason I wore my rubber boots was because they were dirty and I hoped the wave action would clean them.

Most of the beach was cobble, that is, composed of golfball to baseball sized smooth stones. With each step shifting rocks allowed my foot to sink in a bit, it almost felt like I was wading. Off shore, breaking waves (less than 1 metre) formed perfect curls along their tops before crashing down. Beneath the crashing waves, rocks tumbled with the moving water adding their own sound to that of the waves. Constant wave action was moving the rocky beach, in fact, all beaches exist in a constant state of change. At different time of year a beach may look completely different. In summer, gentle waves bring more sand on shore while in the winter, larger waves can remove the sand entirely.

Beaches are made from loose sediments like rock and sand or even ground up hardened lava (Hawaii has beaches like this) that are deposited. A sheltered place in between headlands is ideal as the headlands will take the brunt of wave energy. Beach sediments can originate from a far off river or from right close by. The cliffs overlooking the beach I was on provided all the sediments needed for the beach to form.

As a tangent – my rubber boots are now nice and clean.

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