The phrase “glass sand” would normally make you think of ultra-pure sand resources used in glass-making, such as the sands of Fontainebleau. But I was intrigued by the link that Jules provided in his comment on last Sunday’s sand, a complete inversion of this meaning: sand made from glass. The link was to the Earth Science Picture of the Day (EPOD) for the 7th October that showed a beach on the Hawaiian island of Kauai where much of the sand is composed of glass fragments. That image is reproduced above, and here’s a superb photo of this sand by Tom Amon:
Set in an industrial area of the island, this beach records the reworking of a landfill (in reality, it seems, a euphemism for people simply tossing rubbish into the sea), closed long ago. Huge numbers of glass bottles had been disposed of amongst the waste; these were subsequently smashed, fragmented, pulverised (or that wonderful word, comminuted), rounded, frosted and polished by the ocean. The sand of “Glass Beach” is not exclusively composed of these grains, and the glass fragments are not exclusively sand-sized (although time will tell), but it still comes as a surprise that walking on broken glass is so painless.
The larger pebbles of “sea glass” on Kauai are treasured by collectors of the stuff (vitramarinophiles?) – and this location is by no means unique. There’s another “Glass Beach” near Fort Bragg in California. Its origin is the same: for years the locals simply threw their garbage over the cliffs into the sea, and they threw everything, including cars. In 1967 the area was closed to such activities and is now part of a State Park, the sands riddled with worn glass fragments:
And there are other “glass beaches” around the world, some of them, not surprisingly, around the island of Murano, in the Venice lagoon, home of fine glass-making for more than 700 years; when failures occur, the objects on the left end up as the objects on the right:
But surely, one might ask, if nature can do this so effectively and rapidly, why don’t we? Why not intentionally manufacture sand out of glass as an effective and useful way of recycling? The answer is that we do – to some extent. Broward County, Florida, faces the Atlantic Ocean and includes the metropolis of Fort Lauderdale; the beaches are famous and vital to the local economy – but they have a habit of disappearing under the influence of natural processes and human meddling. For years, millions of tons of sand have been pumped from offshore banks to “nourish” the beaches, at huge costs – and the extent of the operations has now meant that the sand supplies are running out and the offshore environment completely changed. So, also for years, the authorities of Broward County have been supporting a project to evaluate the use of sand made from glass in replenishing their beaches – something already done on the beaches of New Zealand’s Lake Hood and on the Dutch Caribbean Island of Curacao. There’s a good article on this here. The plan would never be to use only recycled glass for beach nourishment, the volumes required being so huge, but as a contribution it would seem like an obvious thing to do – as Commissioner Ilene Lieberman comments, "It's basically sand, so you're just putting it back to its natural state." But nothing is ever that simple. Recycled glass sand is an inert material and therefore, it would seem, environmentally benign and as close to its natural equivalent as you could get; part of the Broward County research has demonstrated this. But no, environmental concerns remain, and, anyway, “The county also wants to do more study on using crushed glass, mixed with natural sand, to boost the beaches. That proposal looked promising … but there's no company in Florida that supplies it, so the cost to study it more is prohibitive for now.” These quotes come from a report from last month of the “controversial sand bypass plans” which would excavate a huge offshore area to trap sand that would then be available for beach nourishment. Of course, this sand would then not be available to Fort Lauderdale, down the coast, and thus the Fort Lauderdale authorities are not impressed.
However, sand made from recycled glass is being used to some extent in concretes (interestingly coloured ones) and other standard aggregate appplications, as well as some sports surfaces, golf bunkers (sand traps) and so on – but we remain less efficient than the processes that create nature’s “glass beaches.”
[There’s a good piece on Glass Beaches here, and on Kauai specifically here. For the Broward County project, see last month’s report in the Sun Sentinel, a good article by Patti Roth, and one of the Project Reports. Fort Bragg beach photos from Microimaging and Jef Poskanzer, Creative Commons license.]