Monday, September 2, 2013

Garden of Pumices

[Michele] High winds this week have blown large amounts of pumice onto the beach these last couple days. In the photo at the right, just about all of the debris at the high tide mark are accumulations of pumice pebbles in various sizes.

OK you might be thinking "Big deal. rocks on the beach, so what?".  This is pumice!  You know, pumice -- the rock with all the holes that you can scrub across your foot callouses.  This rock is abrasive on callouses but it is also so porous that it floats.  On our sail last week we saw rafts of pumice floating on the sea.  Some chunks have been floating for so long that they are encrusted with various algae and critters.

Oh, holey rock!
Maybe now you are thinking, "OK floating rocks that sounds kind of interesting but still why blog about it?". This is pumice!  These rocks formed as volcanic ash welded into clumps as the ash cooled in the air during volcanic eruptions.  The sharp bits in the ash make it great for scrubbing feet but pumice is not strongly welded together.  All in all, pumice is a fairly fragile rock so it doesn't stick around for a long long time.  It tends to break apart so you only find pumice near active volcanoes. OK, you've figured it out now, haven't you.  There are no active volcanoes in far north Queensland.

This pumice must have traveled a crazy distance all the way across the Coral Sea.  Based on recent wind directions, and some recent ocean current data

it seems that the source volcano may be in the New Caledonia or Vanuatu areas about 1500 km to the east of us. Since ocean currents are often more complex than the straight line that I've drawn on the map below, the pumice could be from other sites and could have traveled even farther along a circuitous path.

We've seen some pretty cool things on the beach here, critters, shells and cuttlefish bones. But pumice!  Wow!  That is mind blowing.

UPDATE: News report this morning says that the pumice is from an eruption last year in the Kermadec Islands, north of New Zealand. That is 4000 km from us!

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