Waves at the beach take us to that creative place halfway between order and chaos. Their semi-regulars pulses offer just the right amount of stimulation to keep the brain in train while leaving room for other thoughts to bubble up from the subconscious. And so the beach becomes our catalyst for reflection and a mental as well as a physical experience.
Seaside sources of energy
But waves also define a beach just as it defines our experience of it. It is the energy carried by the waves and dissipated over a sloping shoreline that keeps unconsolidated sediment – which could be sand, shells, pebbles or large rocks – stirred up enough to give a beach it characteristic form and behaviour.
By the 1950s, W. Armstrong Price, a coastal geologist at Texas A&M University, was classifying beaches by the energy in their waves. In Prof. Price’s system, low-energy beaches typically have waves less than a foot (30 centimetres) tall. High-energy beaches are those with waves more than 2 feet (60 centimetres) tall and moderate energy beaches are in between. This dynamic approach to thinking about beaches begins to explaining how and why they change.
Energy translates into mobility for the individual grain or stones that make up beach sediment. They are border dwellers – still part of the land but not entirely committed to it. Inherently we recognize this whenever we pick up a colourful pebble on the beach. Like us, it’s there as a traveller, on an individual journey that could be entirely different from that of its neighbours.
The individuality extends to the smallest scale, and is beautifully captured in the work of U.S. photographer Gary Greenberg. A medical researcher by training who turned to micro-imaging, he is best known for his compelling highly magnified photos of beach sand, which show the striking variety in each grain. The work is a vivid reminder that the individual character of beaches – no two are alike – begins with the raw material they are made from, which ranges from jet black fragments of hardened lava to bleached-white bits of shell or coral. (The brown colour we typically associate with sand is mainly due to natural staining by iron oxide – a.k.a. rust.)
What happens next depends on the precise nature of the physical forces acting on the beach. The formula is simple: A beach is created where land and water do battle. But in true Shakespearean fashion, it’s a third party, the wind, that motivates the conflict.
The three-way interaction is common enough that as much as one-third of the world’s coastlines could be made up of beaches – enough to reach the moon – according to an estimate by Eric Bird of the University of Melbourne’s School of Land and Environment.
But in cosmic terms, a beach must be among the rarest of landforms. The spacecraft sent to explore the other worlds of our solar system have found canyons, volcanoes, deserts and glaciers in abundance. But, so far, only on Saturn’s giant moon Titan, have we seen something that resembles a beach.
Titan is cloaked in a nitrogen atmosphere that is denser than Earth’s and has temperatures frigid enough for methane gas to condense and fall like rain. The methane forms seasonal lakes, which lap up on icy shores as winds blow across the frozen landscape.
On the shore of one such lake (coincidentally named Ontario Lacus after the body of water that sits at the end of my street), NASA’s Cassini spacecraft in 2009 spotted what seems to be a line of beachfront. But instead of water waves breaking on rocks, it would have been formed by methane waves breaking on chunks of ice so cold they’re as hard as rock. Scientists are already dreaming about an amphibious probe that may some day cruise up to such an otherworldly beach.