Rocks again. Just because.

I don't know what to say about these photos, except that I love rocks. Their textures, their shapes, their colours, their slowness; the reminder that this moment passes in an infinitesimal flash to the rocks, in their long, patient dance through the millennia.

These sit today beside the flooded valley that forms Buttle Lake.

The green on the rock face is moss; the yellow may be lichen or pyrite.

From BCGS..., about rock formations a bit further down the road:   There the rocks lie horizontally and are stained with yellow and brown iron oxides derived from the weathering of the mineral pyrite (iron sulphide better known as fool's gold).

How thin a skin our forests (and we) live on!

Pillow lava. I've looked at this pile before. Never get tired of it.

Not exactly pillows to sleep on.

Quoted from earlier posts:

In brief, 

Molten lava commonly erupts from cracks and fissures in the earth's crust onto the ocean floor. Each pillow is formed by lava which squirted forward in front of an advancing, submarine lava flow, like toothpaste from a toothpaste tube. As the lava contacts the colder water it forms a tough crust, like a loaf of bread. However, the molten interior of each pillow makes it relatively plastic and pillows therefore tend to take on weird shapes as they settle and pile up on the ocean floor.(BCGS_IC1995-07)

And from Google Street View:

The pillows continue down to the road. (And underneath it, I'm sure.)

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No sé que decir acerca de estas fotos, aparte de que me encantan las rocas. Sus colores, sus texturas, sus formas, su lentitud; pensar que este momento presente pasa, para las rocas, en un parpadeo infinitesimal en su baile solemne al son de los milenios.

Estas peñas esperan al lado del valle inundado que ahora forma el lago Buttle.

1. Lo verde en la faz de la roca es musgo; lo amarillo puede ser líquenes o tal vez piritas de hierro. 
2. ¡Qué delgada es la capa de suelo donde se establecen nuestros bosques (y nosotros mismos)!
3. He mirado antes este montón de lava acojinada. Nunca me aburre.
4. Viéndolo más de cerca.
5. Los cojines siguen hasta el camino, y debajo del camino también, estoy segura.

De BCGS..., acerca de estructuras rocosas un poco más adelante en este camino: "Allí las rocas descansan horizontalmente y están manchadas con óxidos de hierro amarillos y cafés, derivados del efecto de la intemperie sobre el mineral pirita (sulfuros de hierro, más bien conocidos como "Oro de Tontos").

"Lava fundida sale de grietas y fisuras en la corteza terrestre, emergiendo en el fondo del mar. Cada almohada se forma de lava que se proyecta en frente de un flujo submarino de lava que se exprime como pasta dental de un tubo. Cuando la lava se pone en contacto con el agua fría, se endurece formando una corteza fuerte, como la de una barra de pan. Sin embargo, la parte interior de cada almohada, todavía en estado líquido, la mantiene flexible, y las almohadas (o cojines) adquieren formas extrañas mientras se acumulan una sobre otra en el fondo del agua." (BCGS_IC-19955-07)

Rock-hard pillows

About those lumpy rocks:

A friend sent me a link to a BC government pdf, dealing with the geologic structures of Strathcona Park, which encompasses the central part of the island at this latitude. In it, there is a good explanation of the lumps and bumps. It's pillow lava, ancient underwater lava bubbles. I'll quote from the pdf:

First, a bit of background, from that document.

"... beneath your feet lies a history stretching back 380 million years. It is a history of violent volcanic eruptions on ancient seafloors and quiet interludes when gardens of sea lilies waved in gentle ocean currents. It is a history of rocks torn and folded by the extraordinary forces which can move continents, and of mountain ranges sculpted by the immensely thick ice sheets which only vanished a few thousand years ago."

"The first volcanoes: 380 to 360 million years ago
During the Devonian Period a long gently-curving arc of volcanoes was built by explosive eruptions in the deep eastern Pacific Ocean. These undersea mountains were built up by successive volcanic eruptions and were subject to massive rock slides cascading down their slopes."

These early volcanoes were those that formed the core of the Buttle Lake region.

BC Gov. map, with my added arrow. The Buttle Lake region is that brown patch.

Now those lumpy rocks:

Karmutsen Formation
This 6500-metre-thick pile of basalt flows ... is the most abundant rock unit in the park. About half the mountains, including the highest ones, are carved from these basalts. This formation has a characteristic look from afar; being prominently layered in thick beds and forming reddish-brown dome-shaped peaks. It is also unique close up, as the pillowed form of much of the lava is very distinctive."

These pillow lavas form when basaltic lava erupts under water and is partially chilled by contact with the water. The lava thereby forms a rubbery skin through which more hot lava keeps flowing and expanding. This expansion results in ruptures of the skin and new balloon shaped buds and branches, some of which break off and roll down the slope of the sea floor to form pillows. Over time, the steady submarine eruption of lava, from cracks and fissures, built up a thick, extensive pile of these pillow lavas which totally blanketed the older rocks. They form most of the mountains west of Buttle Lake and south of Upper Campbell Lake and Elk River.

You can see the pillow shapes readily in road cuts along the mine road from about 1.5 kilometres south of park headquarters to beyond Lupin Falls.

Just another cliff face. Composite photo, focus stacked side to side. On the upper right, some pillows are visible.

All this was happening on the sea bed; the pillows formed underwater. With time, the whole shebang moved east and crumpled up to form tall mountains well above water.

I'm halfway through reading the pdf. And already it has cleared up another mystery for me. I'll post about that soon.

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Una amiga me envió un enlace a un documento del gobierno de BC, que explica el misterio de esas rocas redondeadas. Son lava/almohada.

Una traducción aproximada de esta explicación:

... bajo tus pies se extiende una historia que abarca 380 millones de años. Es una historia de erupciones volcánicas violentas en el fondo del mar antiguo y de intervalos tranquilos durante de los cuales jardines de crinóideos (lirios de mar, un animal del filo de los equinodermos) se mecían en los corrientes suaves del oceano. Es una historia de piedras arrancadas y plegadas por las fuerzas extraordinarias que mueven los continentes, una historia de sierras esculpidas por las inmensamente gruesas masas de hielo, las cuales apenas desaparecieron hace unos cuantos miles de años.

Los primeros volcanes: de hace 380 a 360 millones de años:

Durante el período Devónico un arco largo volcánico se formó a causa de erupciones explosivas en las honduras del este del oceano Pacífico. Estas montañas bajo el mar fueron construidas por medio de erupciones consecutiva, se moldeaban por enormes caídas de roca que se deslizaban en sus cuestas.

La formación Karmutsen

Este montón de basalto, de 6.500 metros de grueso es la unidad más común de roca en el parque. Más o menos la mitad de las montañas, incluyendo a las más altas, están formadas de estos basaltos. La formación tiene un aspecto característico vista desde lejos; siendo ordenada visiblemente en capas gruesas y formando cumbres redondeadas de color café rojizo. También de cerca es único, pues la forma de almohadas de mucho de la lava es inconfundible.

Estas lavas acojinadas (almohadillada) se forman cuando lava basáltica hace erupción bajo agua, y el agua la enfría parcialmente. Esta lava enfriada compone una corteza plástica, a manera de hule, cubriendo el flujo de lava fresca, la cual sigue fluyendo y dilatándose. Se rompe esta corteza, y se forman burbujas y nuevas ramas, algunas de las cuales se separan y ruedan cuesta abajo para formar cojines en el fondo del mar. Con el tiempo, la constante erupción submarina de lava desde grietas y fisuras contryó una gruesa capa de estas almohadilladas hasta totalmente cubrir la piedra antigua. Esta capa constituye la mayor parte de las montañas al oeste de Buttle Lake y al sur de Upper Campbell Lake y el Río Elk.

Se pueden ver claramente las formas acojinadas donde se ha cortado la roca para construir el camino desde unos 1,5 kilómetros al sur de la oficina del parque hasta más allá de la Caída Lupin.

Todo esto pasó en el fondo del mar; los cojines se formaron bajo agua. Con el tiempo, todo se trasladó al oeste, apachurrándose contra el continente para formar las altas montañas de nuestra isla.

Apenas he leído la mitad del documento, y ya se me ha aclarado otro misterio. Escribré sobre eso pronto.

Lumpy cliffs

The highways crossing the island follow valleys and lake shores. But the terrain is standing on end, so the road usually runs along a narrow shelf; water at the bottom of a slope on one side, almost vertical rock faces or towering forest on the other, with only a narrow shoulder or ditch separating road from rock. I watch the rock faces as much as I do the lake views.

A wide spot on the highway beside Buttle Lake. Goldenrod, cliffs, forest.

At one spot along the Buttle Lake shore, the rock face turns lumpy, pillowy.

Brown and blue rock.

It looks like something made out of PlayDough.

Same rock, slightly different angle.

I don't remember seeing rock like this before.

Another face, a few curves down the road.

A few more turns, and the cliff faces returned to "normal".

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Las carreteras que cruzan la isla siguen el agua; ríos y lagos. Pero porque el terreno está tan accidentado (mi mamá decía que era una mesa, pero con las patas para arriba), los caminos normalmente ocupan un corte angosto, con el agua allá abajo de un lado, y los bloques verticales de roca del otro.

Me paso mucho del tiempo mientras manejo, mirando esas caras rocosas.

Al lado del lago Buttle, vi estas rocas algo raras; parecen bolas de plastilina todas amonotonadas juntas.

New word: tafoni

Chapter Number Umpteen in "Why I love blogging."

I've been looking at holes in sandstone for a few years, wondering, not knowing how they were made. Twice, I've written posts about them, here and here, mostly full of questions.

And I've been given some answers on Facebook!

The holes have a name: Tafoni.

Sandstone rock with empty tafoni, Edgewater beach, 2010

Tafoni (singular: tafone) are small cave-like features found in granular rock such as sandstone, granite, and sandy-limestone with rounded entrances and smooth concave walls, often connected, adjacent, and/or networked. They often occur in groups that can riddle a hillside, cliff, or other rock formation. They can be found in all climate types, but are most abundant in intertidal areas and semi-arid and arid deserts. (Wikipedia)

"Small cave-like features ..." And "often ... adjacent ..." That describes the ones I find on our beaches. Other sites mention that they can be large, even room-sized, but our shore tafoni are rarely much more than a couple of inches across.

Often the holes line up around the edge of a flat lump of sandstone. This one is on Stories Beach. (No, I didn't put the small stone on top; that's how I found it.)

But what causes these? How do they form, and why? Why in these positions?

Explanations of their formation include salt weathering, differential cementation, structural variation in permeability, wetting-drying, and freezing-thawing cycles, variability in lithology, case hardening and core softening, and/or micro-climate changes and variation (that is, moisture availability). (Wikipedia)

That's a partial answer, but seems to leave out any biological factors. So what about snails and limpets? And the anemones in the pits?

Tafoni full of tiny snails. Willow Point Beach.

Some researchers believe that, in addition to salt weathering, mollusks and other marine life may also initiate tafoni. They do this by creating small holes in the rocky coastlines, where they attach themselves and extract minerals. The hole grows larger over time until eventually the mollusk, or other organism, drops off. The hole is then left to the elements, like wind, rain, and tidal water. (WorldAtlas)

"Salt weathering". What is that?

Mixing salt cations and water can produce a supersaturated solution. When this solution evaporates, salt crystals precipitate in pores spaces. The resulting crystalline solid precipitated between mineral grains can exert stress and readily cause mineral breakdown. (Tafoni.com Weathering)

Several sites explain this in simple terms. Salt weathering shows up on shore rocks periodically wetted with salt spray. In the intertidal zone, the rocks are underwater most of the time, but spend several hours in the open air daily. In the summer, they are exposed to warm sunlight, and dry out completely.

As the rock dries, the salt crystallizes. These salt crystals expand forcefully enough to create small cavities. In intertidal areas, the drying periods are shorter than on the upper shore, so intertidal tafoni tend to be small.

Thousands of tiny snails in tafoni, Willow Point Beach

So here's my idea, so far: the larger sandstone rocks standing above the intertidal floor dry out sooner, and spend more time out of water. This may be part of the reason for the arrangement of the tafoni. Here, salt crystals create small pits in the soft rock. Tiny snails find food in these holes, and dig them deeper; they have the grating radulas for this task. Limpets also bore into rock to create protected sleeping caves.

More weathering occurs. Wind, waves, crystalizing salt, and some chemical reactions depending on the material forming the rock, all may play their part.

And then along come the anemones. Do they enlarge the holes themselves, maybe by chemical means? Or do they just expand to fit the holes they find?

Anemones in sandstone pits, Edgewater beach, 2010

That still leaves the question of arrangement; why do the tafoni so often form along the rim of sandstone piles? Why do they sometimes cover the whole rock? Why do they often riddle one rock in a group and leave the rest free?

Rim tafoni.

The more I learn, the more questions I have.

Such fun!

(The site, Tafoni.com, has much more information, under many headings. Start with Tafoni.com/Definition and go to -Locations to see tafoni on Mars.)

Beach contrasts

Stories beach at low tide is a wide, sandy stretch, perfect for walking, making sand castles, sunbathing, watching the sky ...

Looking northwest, to the coast mountains.

But this afternoon, I turned south, to the seaweedy, slippery, treacherous rocks. That's where the critters live.

Long dikes mini-hogbacks* of sculpted sandstone, interspersed with fields of melon-sized rocks.

Correction sent to me via Messenger from a geologist friend:

Geologically, the sandstone ledges are strata, not dikes, which would crosscut the layers (by definition), and are usually igneous. Because the sandstone layers are at an angle, they could be called mini-hogbacks or cuestas.

Thanks, Jenny!

That green sea lettuce is slippery. I fell once, in spite of extreme caution. But every stone hides a new community.

Sometimes the rocks seem to have been tossed randomly on a flat sandstone table. By giants.

The sandstone mini-hogbacks hold tidepools well above the low tide level. And there are fish in the pools.

Just out of reach, two harlequin duck couples stand watching me.

And yes, there were critters, new and old. And a few mysteries. That's for tomorrow.

A Skywatch post.