The Stacks are Odded Against Us! Subduction's Gift in Southern Oregon and Northern California

Sea stacks on Highway 1 near Elk, in Northern California

Sea stacks are isolated rocky islands found along rugged coasts where wave erosion is intense. They form for a variety of reasons (from glaciers in places like Maine, for instance, or from lava flows in Hawaii). If the rocks vary in composition over short distances, some outcrops will be more resistant to erosion and may last longer against the onslaught of the breakers. This is the gift of subduction in areas like Oregon and Northern California. Rocks exposed along the coast tend to include a hodge-podge of ocean-related rocks, including graywacke sandstone, shale, basaltic ocean crust, limestone, chert, and the occasional seamount (seafloor volcano). Some are really tough, and others are easily eroded.

Sea stacks at Point Orford in Oregon

Subduction happens when a thick slab of oceanic crust and upper mantle (the lithosphere) sinks beneath another slab of lithosphere. The crustal material is drawn into the mantle where some of the rock may melt, producing volcanic activity at the surface above. In Oregon and Northern California the oceanic lithosphere is sinking beneath the edge of the North American continent along what is known as the Cascadia Subduction Zone. The volcanoes of the Cascades Range are the very visible evidence of this intense geologic activity.

Subduction zones produce some of the worst of geologic disasters, including massive earthquakes and devastating tsunamis. But the deformation of the Earth's crust also causes the formation of mountains and rugged coast lines that make some of the world's most beautiful scenery. And that is where today's post originates. I had the privilege of spending a few days making my way south along Oregon 101 and Highway 1 in Northern California on my way home from Christmas visits, and we saw a stunning variety of shoreline features including the sea stacks that I am emphasizing today.

Sea stacks near Brookings, Oregon, I think. Anyone recognize them?

The Cascadia Subduction Zone has also collected bits and pieces of continents from elsewhere (called exotic terranes) and mashed them into the edge of the continent. The rocks of the Klamath Mountains in southern Oregon and Northern California originated in this fashion. These metamorphic rocks contribute to the extreme variety of rocks found along the coast.

Restless seas in the morning at Fort Bragg in Northern California

The weather was supremely perfect for viewing the scenery (if not an utter disaster in the making for water-planners; the ongoing drought is the worst ever). There are storms out there somewhere because the waves were quite large at times.

At the mouth of the Navarro River just south of Mendocino in Northern California

This isn't the first time I've used the dumb pun above; I put up a series of sea stack pictures last year when I made my first journey down the Oregon coast in many years. The thing is, these stacks are completely different. There is a lot of very spectacular scenery, and every trip along that route will be a different experience.

Sea arch in a stack at Navarro Beach in Northern California near Mendocino.

Navarro Beach was our last long stop. We actually had to get home at some point after two weeks on the road. It was a truly beautiful day. Happy New Year to all!

Sea stacks at Navarro Beach on the Northern California coast.

Where the Sierra Nevada Rises From the Sea: The Granitic Rocks of Garrapata State Park

We've reached the next beach on our exploration of the most beautiful coastline in the world, the one extending from Big Sur to Bodega Bay in Central California (register your arguments in the comments about your own interpretation of "most beautiful"!). It's called Garrapata State Park, and it offers some nice shorelines carved into the granitic rock of the Salinian Block, the displaced terrane of Sierra Nevada rocks that now forms a mountain range sloping directly into the sea.

Garrapata doesn't quite have the prominence of Julia Pfeiffer Burns State Park, or Point Lobos. There are no visitor centers and no campgrounds, and in fact, few tourist facilities at any kind. No parking lots or admission booths. Just a table or two and some fine trails. It is pretty much a wilderness park, aside from the intrusion of Highway 1.

The coastal terrace at Garrapata was covered in wildflowers despite the late season when we visited. Above we can see an Indian Paintbrush. I'd try to identify it, wondering if it was the rare Monterey variety, but became aware that with more than 200 species, I probably wouldn't be successful at nailing it down.

The rocky coastline reveals some of the best exposures of the granitic rocks of the Salinian Block. I use the term 'granitic' because the petrologists who study igneous rocks are rather specific when they classify the light colored grainy plutonic rocks that normal people call 'granite'. The proportions of the minerals that make up the rock (quartz, orthoclase feldspar, plagioclase feldspar) determine whether the rock is granite, granodiorite, tonalite, diorite and others. On this part of the coast, the rock is identified as the porphyritic granodiorite of Monterey. Granodiorite contains a higher proportion of plagioclase than granite has. The term 'porphyritic' means that the rock contains much larger crystals of feldspar in a finer matrix of other crystals,

The rock formed as molten plutons deep in the crust. The rocks cooled slowly over thousands of years, allowing the crystals to grow to visible size. The granitic rock is monolithic while it remains at depth, but when it is exposed by erosion, the release of pressure allows the rock to expand. It does, but not like a marshmallow. It breaks into vertical and horizontal fractures called joints.

Ocean waves do a great job of exploiting the joints and fissures, tearing the rocks up and producing rugged sea cliffs and offshore rock islands called sea stacks.When waves impact against the rocks, they can exert pressure on the order of several tons per square foot, and air is compressed in fractures to the same degree.

Waves can widen joint systems, forming sea caves, like those seen below.. I don't know how far the caves at Garrapata extend, but some on the north coast are hundreds of feet long, and navigable by kayak.

The kid in me wants so badly to explore caves like these. I don't think the California coast had much of a history with pirates, but I could imagine treasures being hidden in the backs of some of these caves.

Garrapata State Park also exposes an excellent example of a nonconformity. Unconformities of all kinds are buried surfaces where erosion once took place. A nonconformity develops when plutonic or metamorphic rocks are exposed at the Earth's surface by erosion. Later, the surface was covered with sediments, in this case conglomerate deposited by streams flowing across the coastal terrace. Wave erosion later exposed the relationship seen in the photo below.

Terraces are not especially common along the Big Sur coast, but a modest one can be explored at Garrapata. Terraces result when the back and forth of wave action on a beach forms a more or less horizontal wave-cut bench. If sea level falls or the land rises, the bench is lifted above the wave zone to form a flat surface surrounded by coastal cliffs leading down to the water below. The terrace was covered with colorful vegetation due to the stable deep soils.

It isn't maybe fully recognized by most tourists, but every sea stack and small island on the California coast is part of California Coastal National Monument, established in 2000 by presidential proclamation. There are around 20,000 such rocks along the 1,100 miles of the California shoreline!

Our last little discovery of the day was a small waterfall that developed where Soberanes Creek flows across the coastal terrace and trickles into small cove. It was a colorful intersection of rock, water, and life.

Next stop: the point of the sea wolves!

Addendum: one of my Facebook friends pointed out what a terrible name Garrapata actually is: Tick. It reminds me of Avenida de Las Pulgas near Menlo Park in the Bay Area: the Avenue of the Fleas. It's really true: all place names sound better in Spanish!

Where the Sierra Nevada Rises From the Sea: Not the Easiest Beach to Find

A pleasant country road winds for a few miles through redwood forest and thickets of brush and poison oak to a secluded hidden beach. I've been through the region maybe a dozen times, but I never noticed the road branching off of Highway 1, and I usually traveled without detailed maps (really, can you believe THAT??). There are no signs, not even one giving the road a name (it's officially Sycamore Canyon Road for the record). Once you know it exists, it's not too hard to locate it, so I will leave you to your own devices on finding it for yourself.

In any case, there is a beach along the Big Sur Coast. That is actually rather extraordinary, given the way that the mountains rise from the sea. In most places there are steep inaccessible cliffs. Beaches can only form where sheltered coves allow sand to accumulate, sometimes at the deltas of creeks and rivers. The beach we are exploring today is Pfeiffer Beach, a section of coastline in the boundaries of Los Padres National Forest, but managed by the California Coastal Conservancy (I admit I've never understood how the federally-owned national forests of Big Sur were never made into national parks).

See? They really do welcome you to Pfeiffer Beach...once you find it.

There is a modest amount of parking available, and simple toilets (which is one of several possible explanations why the beach is so well hidden; it would be overwhelmed by crowds). The beach is just a few hundred yards down a sandy trail.

The very modest creek in Sycamore Canyon doesn't seem a likely candidate for producing enough sand to support a permanent beach, but some sand may be drifting along the coast from the north. The rocky sea stacks on the outer part of the beach provide an explanation for the accumulation of sand at Pfeiffer. They break up the wave energy so only relatively small waves ever impact on the beach. The sandbar is termed a tombolo, though it is not so perfect as to be a textbook example. A tombolo is a sandbar that connects an offshore sea stack with a coastline (look for a textbook example in a near future post).

The rocks include graywacke and metavolcanic greenstones of the Franciscan Complex. They formed in the guts of a subduction zone/trench system, and as such have been churned and mixed. The sea stacks are constantly pounded by the surf and have produced a group of sea arches visible from the beach.

The rock isn't right, but doesn't the shape of the hill in the picture below recall Diamond Head in Oahu, Hawaii? It's just missing a long string of high-rise hotels, and what a shame that would be here on the Big Sur coast.

From a more southerly vantage point on the beach, the tombolo is a bit clearer, connecting the sea stack on the left with the coastal cliffs on the right. The scrub covered slopes also hide some biological treasures (see page 18 of the road guide): the site includes the southern range limit for Little Sur manzanita, the rare Monterey Indian paintbrush (Castilleja latifolia), bear grass (Xerophyllum tenax); and the northern range limit for California peony (Paeonia californica). Not that I knew what I was seeing...

One more notable feature of Pfeiffer Beach is the purple sands. The beach sand is mostly composed of quartz, but streaks of the purple sand can be occasionally found. The color comes from the presence of grains of garnet in the sediment. I've now seen red, yellow, white, black, gray, purple, and green sand beaches.

See my previous posts for an explanation of the Sierra Nevada connection.

Watching a Slow Motion Apocalypse: The Relentless Erosion of the Sea

Now that the apocalypse is over and the world is ended we can get back to life and celebrate what is beautiful about our planet. I wasn't going to take the chance that the world would end with me sitting on a couch at home bored, so I was on the road on the northern California-southern Oregon coast during a pretty major storm. A couple of feet of snow was expected in the mountains, along with several inches of rain in the coastal areas and some very high winds. It was not a day for photography: dark skies and rain made things pretty tough. I only got a few photos that I thought were worth sharing.

We were at the Kuchel Visitor Center in Redwood National Park near Orick, California for a short break. I wandered down towards the beach (without a jacket as usual) and snapped a few shots of the sea stacks just offshore. The surf was running at 10-15 feet and maybe more, and the wind was whipping spray off the whitecaps, making for a violent geologic environment.

Large winter waves are among the most powerful of the forces in geology, capable of dislodging huge blocks of rock and tumbling them to sand in an incredibly short period of time. One can look at these sea stacks and consider how short a time they will exist before disappearing into the surf. Or...one can consider that they are the last remnants of what used to be land. Erosion is a relentless power that is continually and forever changing the face of our planet despite our best efforts to contain it.

Worried about apocalypses? It's fun to play with the concept sometimes (I love some of the Google+ and Facebook posters today), but really, it's pretty conceited of us to think that we are such a twisted generation that we get to see the end of the world. There have been plenty of people worse than us in the past, and in the future there will be plenty more. The world isn't going to end. But we do have the power to change the world into a slightly better place before we leave it. The real apocalypse is taking place slowly, one grain of sand at a time. The world will change and all things will pass away. But we have been given a short period of consciousness, and the company of many others, and we have choices about what we do with our short existence on planet Earth.

The Stacks are Odded Against Me...The Southern Coast of Oregon

Arch Rock Overlook along the Samuel Boardman State Scenic Corridor

If you have read this geoblog for any length of time, you know that I have a special spot in my heart for California. We get maligned for smog, traffic, riots, wildfires, and whatnot, but there are reasons so many of us live here. It's got some of the most wonderful geology in the world, and the geology makes it an interesting place to live...the hills and bay of San Francisco, the mountains surrounding Los Angeles, and the coastal hills of San Diego, for instance. I've spent a lot of time talking about the Other California, too, the places that are not so well known. And then there is the coast: Big Sur, the Marin Headlands, Santa Barbara, and Malibu. All told, some of the greatest scenery to be found anywhere.

But once in a while, I am willing to grant that some other places are truly spectacular, too. I certainly love the southwest, as the blogs of the past month show (those will continue soon). But I made a trip up the coast this week, from northern California to Washington, and believe it or not, followed the Oregon coastline for the first time in my life.

I am willing to allow that the Oregon coastline is a very beautiful place to travel...

Part of the wonder of the place is the preponderance of sea stacks (hence, today's title). Sea stacks are generally defined as vertical rocks and small islands that are separated from the coastline by open water. A stack may end up connected to the mainland by a sandbar called a tombolo (above, at Myers Creek beach).

We spent the most time at Arch Rock Overlook along the Samuel H. Boardman State Scenic Corridor north of Brookings. The sun had come out, and in moments I was under the spell of this place...

A sea arch is a sea stack or headland with a hole in it. There was a truly fine example at the...ahem...Arch Rock Overlook.

The sea stack that I loved more than any other that day was to be found at Cape Blanco. It just struck me as unique, all by itself on the beach below. Cape Blanco is the westernmost point in Oregon, and arguments have raged over whether it is the westernmost point in the United States (I guess part of the argument is whether one counts the rocks exposed at low tide or high tide). For the lighthouse aficionados among you, Cape Blanco also has the oldest lighthouse in the state, built in 1870 or so.

Here is the same sea stack at Cape Blanco from another angle. It really is all by itself out there! Oregonians: does it have a name? I couldn't find one anywhere.

I'm still on the road, so posts will probably continue to be irregular. I love seeing new places!