Tidal Bores: The ‘Wild Boars’ of the Sea
This is a tidal bore; a “true” tidal wave. Despite what those in Hollywood oftentimes suggest in their films, these waves occur when the force of a strong tide meets the force of a river current. Tides are caused by the effects of moon’s gravity here on earth. The sun also has some influence on our tides, however given the sun’s much more distant location, the moon is the primary influence.
Although the list is not limited to these locations, some of the most famous places where these surges occur include the Bay of Fundy between New Brunswick and Nova Scotia in Canada, the Batang River in Malaysia, and at the mouth of the Amazon River. Ranging in their strength and ferocity, some tidal waves barely make a crest in the water while others are known to be rougher and more forceful, such as the Turnagain Arm Bore which occurs in Alaska, US.
The depth and velocity of tidal bores vary from location to location. They depend on the depth of the river and ocean, the topography of the surrounding area, and also which season it is. Some bores such as the Pororoca Bore at the mouth of the Amazon only occur during spring. During that time of year, the area experiences some of the strongest tidal pulls from the moon and as a result, the ocean can produce a wave strong enough to surge up the Amazon.
Not only do these tidal bores directly influence the river currents and inlet depths, but the ecology of the area is also dramatically impacted as well. Crocodiles, for example, are known to follow the Styx River bore in Queensland, Australia. They do this so that they can pick off any fish that have become disoriented from the surge of the water. Likewise, bears and other opportunists are commonly found on the banks of Alaska, looking for an easy meal after a tidal bore rolls through.
It is truly astounding when one considers all of the different ways in which our sun and moon affect us here on earth; perhaps none more visible than tides and tidal bores. Sitting on the beach, or on the coast of some river mouths, one can literally watch the power of the moon’s gravity. Despite the incomprehensible distance between the sun and us or the moon and us, we can still witness their presences here on earth in so many ways other than looking up into the sky. That in itself is just so awesome.
–Pete D
Photo Credit: Scott Dickerson www.surfalaska.net
References: 1. http://hyperphysics.phy-astr.gsu.edu/hbase/waves/tidbore.html 2. http://education.nationalgeographic.com/education/encyclopedia/tidal-bore/?ar_a=1 3. http://www.scienceandthesea.org/index.php?option=com_content&task=view&id=104&Itemid=10 4. http://www.tidalbore.info/tour.html
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