Record ripples

Years ago I did quite a bit of research trying to develop computer models for the formation of sand ripples. These models took individual (model) grains of sand and moved them around repeatedly according to a set of simple, sensible rules. For example, sand grains that were sitting at the top of bumps moved further forwards than grains in lower, and so potentially more sheltered, positions. When it comes to research I do have a tendency to follow my instinct and at that time I had an idea that if you leave a set of ripples to develop over really long timescales they just get bigger and bigger. However, in practice, it would look like they had stopped growing because once they become large any noticeable change in their size takes absolutely ages to show up (apart from my intuition there is also some other evidence from mathematical models that this might be true – up to a point).

So, I was interested to read in New Scientist, Issue 2703 [11 April 2009] about some wind-blow ripples that have been found on the Puna plateau in Argentina which are up to 2.3 metres high and 43 metres long (which is three times the height and two times the length of the previous record ripples). I don’t know any details, but it does seem to me that the Puna plateau is exactly the sort of place where ripples might be able to develop unhindered for really long time periods, so these massive ripples provide me with some reassurance that my instinct was correct. Apparently, there may be even bigger ripples on Mars…