It was late last night and I've jumbled my dune theory. Will now try to recover with grace. I might have a degree in Marine Science but darned if I can remember it - never used it! Where's Bean when you need her - HELP!!

The foredune is the first line of dunes on a beach - there is often a lagoon on the inland side - try the US Atlantic coast frinstance, or Baja California in Mexico. The foredune's role in life is to act as a reservoir of sand - to be utilised during storm surges. The more energetic wave action during storms attacks the foredune, eroding it. The beach changes profile during this process, becoming shallower and hence sapping the energy of the waves. They break increasingly further out to sea and thus inflict less damage at the top of the beach.

This is the principal reason that fixing the foredune (with buildings especially) is a BAD idea. No reservoir of sand, no attenuation of waves, no stopping the sea, crash/topple go the buildings.

Back to dune cross sections.....they are typically asymmetrical - steeper on the lee side and shallower on the windward side. A dune advances when sand blown up the windward face passes over the crest and tumbles down the lee face. When a dune (or ripple mark if the structure is formed underwater - with an obvious difference in scale of course), the strata parallel to the leeward side are known as the foreset beds (Dyslexia joke - "Run Foreset, run!!) - they are formed at the forefront of the dune and indicate its direction of movement. The flatter strata that develop on the windward side form the topset beds.

Bit more trivia: the angle that the face makes with the horizontal is the angle of repose. This is a function of grain size, sphericity, moisture content and specific gravity (good ol' SG - welcome back!!) It is typically 30 something degrees for many materials - 34 degrees for your standard garden variety beach sand I think. Bloody steep when you're on it!!

Edit: Had a quick squiz at the Dictionary - there's plenty of "fore" words that have been developed without an "aft" equivalent. Another that I thought of is fo'c'sle - never heard of an aftc'sle on a boat.

stales