Tag Archives: geology

On Sand and the Making of Castles

By Randy Jackson

To build a snow fort or sand castle? That is the (real) question. At this time of year, some northerners enjoying Huatulco might be wondering if their snow-fort building skills are transferable to constructing a sand castle. The short answer is no. But the desire to create an objet d’art out of something you try not to track in the house shows the right attitude. To build a moderately impressive sand castle involves five simple steps following the acronym LWBSF, and remembered by the phrase: Leave Winter Before Soul Freezes. Just two pieces of equipment are needed: A good sized bucket for hauling water, and something to sculpt with.

LOCATION: Choose a location. First choose a beach, one of the bays of Huatulco based on the type of sand. The more powdery the sand, the better it will compact for a lasting structure. Grainy beaches like Cacaluta are not good for sand castles. Once on the beach, choose the location of the castle itself. A place where the sand is moist below the surface is best. The farther from the water, the longer the water-hauling trips. And, of course, you want a spot above the high tide line.

Sand: As an avid hiker in the Canadian Rockies, I sometimes stand on some majestic rocky peak and grapple with the time scale it would take for the rock beneath my boots to become sand on a beach. It will, eventually. Sand is ground or eroded rock. Ocean waves do some of the work bashing against rocky shores, but streams bring most beach sand from rocky areas to rivers, then to oceans, where currents and tides deposit the granules back on land to make a sandy beach. Once a granule is chipped off a rock somewhere on a continent, it takes about one million years to move that granule each 100 miles along waterways. Think of the eons of time we could save if we all brought a jar of sand down on the plane.

WET DOWN THE AREA: Often a good location for a sand castle is closer to a beach restaurant where beverages can be supplied to the castle builder, but this usually means the sand is dry. Mark out a six-foot square with your foot. Then haul buckets of water up to this spot to soak the sand at least to the depth of one foot.

Sand: Not all sand is the same – there are some differences in the sand even among the bays of Huatulco. Around the world, sand comes in six different colours: white, grey, black, pink, green (yes, green – the most famous is a green beach in Hawaii), and the most common, golden or brown. Consistency of the grains also varies widely. Desert sand differs from beach sand. Beach sand and sand mined from river areas is in great demand, whereas desert sand has few uses. The issue with desert sand is that the grains of sand journey to the desert overland, blown by the wind. This makes the desert sand grains smooth and rounded, and rounded grains don’t bind well even in concrete. It’s the angular grains delivered through rivers and oceans that allow for bonding between grains and allows for compaction. Dubai, for example, has imported millions of tons of sand from Australia to build their new islands for condo towers. Their own nearby desert sand is of no use.

BUILD A VOLCANO: When the sand in your spot is sufficiently soaked, build a base in the shape of a volcano. Dig the sand up around the sides of a base about three feet across and keep piling it on, up to a height of about three feet. Keep flattening the top as you go. Once the sand volcano is high enough, scoop a crater out of the flattened top.

Sand: Sand is the second most-consumed natural resource on the planet, right after water. Cement is by far the biggest use for sand. But there are other substantial uses as well. Asphalt, glass and computer chips use significant quantities of sand. Civilization as we know it could not exist without the buildings, roads, and computer chips that are made from sand. Although in geological time, sand is a renewable resource, on a human timescale sand is a limited resource.

Demand for sand is outstripping supply. Most Southeast Asian countries have banned or restricted the export of sand. Sand mining has completely obliterated at least two dozen islands in Indonesia since 2005. The main culprit – Singapore, the world’s largest sand importer. Singapore wants to make more land, and sand is the best material for that. The Times of India has reported that the Illegal sand trade amounts to $2.3 billion per year. There have been hundreds of killings between “Sand Mafias” in India. Even beaches themselves are a source of demand for sand. The US Geological Survey estimated that two thirds of Southern California beaches may be gone by 2100 – only 80 years down the road. Moreover, virtually all of California’s water flows into the ocean are dammed and used upstream. This means the natural erosion of beaches is outstripping the natural sources of supply.

Remember in the movie, The Graduate, where Mr. McGuire (Walter Brooke) says to Benjamin Braddock (Dustin Hoffman), “I just have one word for you – plastics”? He could have said “Sand.”

SOAK THE VOLCANO: Haul more water and pour it slowly into the crater on top of your sand volcano. Physics experiments have shown the optimum strength in sand structures has the ratio of eight parts sand to one part of water. Keep patting the sides of the volcano. Haul sufficient water until the flattened top of the volcano seems solid when you push down on it. Once this is done, flatten the top out further so it no longer looks as much like a volcano. You will now have the base of your sand castle, and it should last for more than a day.

Sand: Given sufficient geological time, with the gradual erosion of continental mountains into sand, will the earth one day be a planet of sand, as in the book/movie Dune? No: Very slooooooowly, rock makes sand, and sand eventually makes new rock. Sand settles in certain places where winds and currents leaves it. More gets added, and more and more, and the weight of the sand compacts and pushes the sand deeper and deeper into the earth. Pressure, temperature, and chemical reactions eventually transform sand into sedimentary rock. Yada yada … , and eventually tectonic plates push that sand-made-rock up to form new mountain ranges.

FREEHAND SCULPTURE: Here is where you need a wood sculpting tool. A wooden ruler is ideal, although one of the wooden book markers that vendors pedddle on the beach works OK, too. Begin by squaring out the sides of your flattened sand volcano. Next, scoop sand into your bucket, about 1/3rd full. Add to that enough water to easily cover the sand and let the sand settle into the bottom, below the surface of the water. After a minute or so, scoop out a handful of wet sand from the bucket and work it between your hands until enough water is pressed out to make a mucky ball. Place the ball on the top of your sand base, near the edge, making small piles about eight inches high. Each pile you make will become your castle turrets.

Once your blobs have been arranged all around the edge, use your sculpting tool to carve the sides into circular turrets. Notches can be carefully carved out of the turret tops. Use your sculpting tool to make a brick looking crosshatch in the turrets and the base of the castle. Use the soaked sand to add other features like walls between the turrets and a drawbridge.

Knowing a bit about sand makes the construction of a sand castle a kind of celebration. Celebrating that in the face of geological forces and time scales beyond our comprehension, we are here on a beach, making something from a substance the earth itself uses like playdough. True, our structure lasts a day, mountain ranges somewhat longer. Yet, both are temporary, on different time scales. But then again, who tries to contemplate all that when the air is warm, the waves are washing ashore, and you’ve built an outdoor structure without having to wear your snowsuit!