SOME QUESTIONS ANSWERED
Q. WHY DOES SAND VARY IN COLOUR FROM BEACH TO BEACH? REFLECTIONS North coast sands are subtle versions of a very pale whitish-yellow, stained black in parts (see later). Usually the more quartz, the paler the sand. On sunny days there is a strong glare off the sand because it is being reflected in the trillions of tiny quartz grains. Some beaches are slightly darker simply because of differences in rock and mineral types. Rivers and loughs feed into the sea daily payloads of soil and other organic matter which is washed and sorted by the sea before being deposited on shore by the tide. MAGNETIC SAND Rocks are continually being eroded by Mineral Magnetite J.A.
the elements, providing a rich bank of mineral-rich sediment. Because the rock type of the north coast is predominantly dark basalt there is a strong grey-black tone to the sand colour. As an igneous rock (volcanic in origin) basalt contains a mineral called magnetite from the earth’s core which is magnetic. Therefore part of the north coast’s sands are also magnetic (see Beachcomber’s tip). Large deposits of black magnetite mineral on the beach, especially after storms can often give the impression that it is stained with oil (see p.35). Beachcomber’s tip: Take a sample of blackened sand, place it on a piece of paper, allow it to dry in the sun and then use a magnet beneath the paper to separate out the magnetite.
Q. HOW DEEP IS THE SAND? BARS Sand depth varies from beach to beach. North coast sands can be several metres deep with some exceptions, where it is little more than a thin coating. Every winter Runkerry near PortBallintrae, appears to lose its sand leaving nothing but boulders where once there was a beach. This is due to annual storms pulling the sand seaward and dumping it just offshore in the form of one or two large sand bars. Locals can point out the waves breaking on these sand bars during winter months. The sand slowly returns to shore during springtime when the weather settles down returning the beach once again to its visitors. The famous Tunns sand bank (taken from the Irish word ‘an tuian’ meaning wave) just 1 mile off Magilligan Point famously builds up every number of years, to a point where it is exposed enough to land on. In 1994, a charity rugby match was played on it.
Published on Jun 15, 2011