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| April 27, 2020 Post 115 |
| Lake Ontario’s ancient sands of time |
Most of the south shore is made up of gravel and cobbles though there are a few stretches of sand at Hamlin Beach State Park, near the Genesee River, at Sodus Point and Fair Haven’s state park. At the lake’s east end miles of sand has accumulated and persisted. At some locations man made structures and changes to the shore might be causing sand accumulations.In the photo above a recent storm has moved gravel onto the State Park's jetty enhanced sandy shore inside Little Sodus Bay.
However, at least three locations seem to have had sandy shores long before any human modification of the coasts had been made. These are natural areas where currents and long shore drift have worked to deposit sand after its erosion.
While the beach itself may change, the individual grains of sand are all but indestructible. Our Lake Ontario beach sand is mineral sand. If you take a hand lens and peer at a pinch of sand you’ll see a variety of colored grains, each grain representing a mineral. Our sand is made up of reddish garnet, dark hornblende, light colored quartz and other minerals grains created by the breakdown and weathering of ancient rocks. The sand and cobbles of the lake’s south shore erode mainly from the shoreline though some also comes from the lake bottom near shore. Moved and mixed by the glacier, this “till” was originally deposited during the ice’s retreat. The sand is now sorted out from the cobbles and clay by water movement as the land
If you look closely at a mud flow at the foot of a lakeshore bluff after a heavy rain, you’ll see the mud often looks a lot like the outwash from desert highlands as seen from 30,000 feet during a transcontinental flight. It’s the exact same mechanism on a microscale as the heavier sand grains trace the path of the flowing water’s miniature channels through the finer clay particles of the tiny delta. ( see second photo)
Once sand makes it to the beach it’s subject to the forces of both water and wind. If the beach sand dries out, it then readily moves inland with the wind to form dunes. Sometimes you may see small darker patches on the surface of the sand. In the past I had thought this was some form of pollution, perhaps oil or coal tar, deposited on the sand. But these purplish or black marks are more likely to be result of sorting. Sand grains of garnet or other minerals that are heavier than the lighter colors of minerals are sorted by density when subject to gentle swashing of wavelets. The result can be small patches of darker sand. If you look closely at the photo you can see some faint smudges of contrasting co
The experts tell us that our sand is far more ancient than many of the beach pebbles underfoot. Derived from mountain rocks and inland outcrops, shifted and shoved by running water and then, just a moment ago in geologic time, released from a shoreline bluff, now it moves on down the shore propelled by long shore transport currents.
Lake Ontario sand is “sharp” sand. It’s been waterborne during its long life. Wind blown sand grains like those of the desert or from some marine beaches, are more rounded. This sand makes an inferior mortar mix and is less valuable to commerce. Concrete is a mix of powdered limestone cement and sand. Sharp sand makes far more durable mortar. A neighborhood in San Diego called North Park during a recent spell of gentrification saw many of the little craftsman bungalows that dated to the early 1900 jacked up and given new foundations. Their original footers had cracked and crumbled over the years, because they were made of local wi
As you stand upon the lake’s eastern sandy shores or slog through the loose sand of Prince Edward County’s big dunes, it’s hard to imagine that there is a shortage of sand. Experts tell us that next to water, it is now the most widely used natural resource in the world. Relentless construction booms have led to sand wars and shortages in India, Indonesia, China and elsewhere. Construction firms have dug up beaches and dredged rivers and have pushed into agricultural areas to strip mine sand deposits. Sometimes farmers and other landowners who objected have ended up mysteriously murdered.
Some have claimed by the end of the 21st century that the natural beach will have become extinct from sand mining and other causes. Fortunately, we in New York State still seem to have plenty of sand suitable for mortar mixes, though other man made forces do threaten Lake Ontario’s sand beaches.