The roughly twice-daily ocean tides ebb and flow on different timescales and to different heights depending on the relative orientations of the Sun and Moon.  It is the gravitational pull of these the two bodies that are responsible for our tides, a fact first explained by Isaac Newton.  When the Moon is full (and again when it is new), it, the Earth and the Sun are nearly aligned – a situation know as syzygy (one of my favorite words). In this orientation, the tidals forces combine to amplify the tidal surge; we have a spring tide.  Throw in some big surf and an unusually close Moon, and you’ve got quite a shorebreak.

This was the case this morning at about 9am near my home in Solana Beach, when a 7.4 foot high tide came in just a few hours after the full Moon had set (note the lag between the Moon/Sun location and the peak tide – this has to do with how long it takes the ocean water to respond to the tidal force).  This particular full Moon was a special one because the Moon is currently at perigee in its orbit – the closet it comes to the Earth.  This makes the tidal force that much stronger, and results in what is known as a perigean spring tide.

What’s more, we had big swells in the NOAA forecast:

CAZ043-302200-
 SAN DIEGO COUNTY COASTAL AREAS-
 200 AM PST SAT JAN 30 2010
 
 ...HIGH SURF ADVISORY SATURDAY THROUGH SUNDAY...
 
 ...HIGH RIP CURRENT RISK...
 
 .THIS AFTERNOON THROUGH SATURDAY...
 SURF HEIGHT.............5 TO 8 FEET. 
 RIP CURRENT POTENTIAL...HIGH. VERY STRONG CURRENTS AND DANGEROUS
                         SWIMMING CONDITIONS ARE EXPECTED.
 WATER TEMPERATURE.......58 TO 60 DEGREES.
 
 REMARKS...BIGGEST SETS LATE IN THE DAY.
 
 OUTLOOK FOR SUNDAY...6 TO 8 FEET. MAX SETS 9 FEET.

All this combined to make for some pretty strong waves pounding the cliffsides of Solana Beach.

I snapped some photos of the shorebreak and also brought my audio recorder down to try to capture some of the action in sound (see below).  Most of what you hear is the swish of the waves crashing on shore, followed by the roll of water over the shingle beach rocks as it pours back out.  Occasionally you hear a loud rattle, like someone shaking stones in a tin can.  These are indeed stones – up to 6 inches across – being thrown around the bottom platform of the stairs by the bigger waves.  There are also some low booms when the waves crash against the cliffside, wind blown off the cliffs when large breakers come in, and even a plane overhead!

It’s a beautiful, dynamic ocean to watch.  Be sure to keep safe.

Audio

The following is a 10-minute recording of the waves from the staircase shown in the photos below.  The original mp3 file (9.2 Mb) can be found here.

Images

Shorebreak coming onto shore during a perigean spring tide

Waves crashing on the cliffside in Solana Beach

Explosive surf at the bottom of the stairwell

Pre- and post-surge at the stairwell

A hungry little breaker

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