Local Walks: Tofoni at Larrabee

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10. Dried eelgrass on the rocks.

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These photos are a celebration of tafoni* and accompanying formations in the rock at Larrabee State Park, along with two vistas so you can see the context. And there are children enjoying their finds before returning them to the water, and two intertidal denizens called Purple sea stars.

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Tafoni – in Sicilian it means windows (or so I read in Wikipedia). And in Corsica, taffoni (with two “f’s”) also means windows (says Wiki). The tafoni we’re talking about could be related to a Greek word for tomb, taphos but in any case, the window/tombs I’m thinking about are sensuously sculpted holes in rock. Tafoni is a term geologists use for certain the intricate patterns that occur in rocks from complex weathering processes.

This phenomenon can be found in the desert and at the shore, and the shore is where these photographs were made, at Larrabee State Park in northwestern Washington.

Larrabee was Washington’s first state park, thanks to a wealthy family who donated some beautiful waterfront acreage to the state over a hundred years ago. Primarily a rocky stretch of saltwater coast, the park also includes the west side of Chuckanut Mountain. The cliffs there are very steep: last year a man died in a fall from the rocks, and a couple was injured in another fall this year. The narrow, winding road that passes through Larrabee is full of blind curves and marvelous scenic views which you can enjoy as long as you remember to pay attention to where your tires are. After arriving at Larrabee I like to cross under the railroad tracks and follow the easier paths along the shoreline. The rocky beach is great to explore at low tide when tidepools reveal all sorts of creatures.

Maybe because they’re more dependable than sea life, the rock formations are the big draw for me. Whether the rocks are towering over the shoreline or defining it, the 57-million-year-old sandstone displays many fascinating forms. You can’t help but wonder how the tafoni and the smooth, svelte curves came about. The process of honeycomb weathering (those Swiss cheesy holes in the rocks) is fairly complex. It begins with the process of physical weathering, a loosening of the structure of the rock caused by a tree root, freeze and thaw cycles, the action of wind, acid rain…a myriad of forces that work on rocks to alter their shape. At Larrabee the rock is quite permeable. It’s subject to salt from ocean water, carried from many miles away by the tides and storms. Salt water splashes on the rocks, leaving salt crystals between grains of rock as it dries. The salt crystals grow, pushing grains of rock aside, a process that happens readily because sandstone here is quite porous. Certain minerals in the sandstone are more susceptible to salt crystallization than others and once a pit begins it can increase its size more quickly than the surrounding rock, so weathering can be very uneven.

Add to this the effect of algae growing on the surface of the rocks. Where algae grows, the rock absorbs water much more slowly so weathering is retarded. In places without algae the rock is eaten away faster, expanding into a hole. There is controversy about the exact science here and frankly, this is as much detail as I can absorb! If you’re interested, Dave Tucker at Northwest Geology Field Trips points to further discussions of tafoni in a blog entry here.

Better yet, visit this little stretch of shoreline and admire the rocks in person. Run your hand along the surface – it may look smooth but it’s not; the grains are large and rough, providing nice handholds if you want to scramble. Or locate a place close to you where honeycomb weathering can be found. Altdahn Castle in the Palatinate Forest of Germany, Mt. Wellington in Tamania, and Arches NP in the US are some examples, and here’s a map of the world with tafoni locations. Check it out. And bring your camera.