(Petrified) Forests of Stone
Despite being comprised almost entirely of quartz, trace amounts of elements like iron and manganese give petrified wood its myriad of colors.
I grew up about 90 minutes away from Petrified Forest National Park and, aside for a quick lunch stop about 10 years ago, had never visited before last week. While this is nowhere near as inexcusable as living in Arizona for decades and never visiting the Grand Canyon (yes, such individuals exist…I’ve met many), it still seemed like a bit of an oversight on my part. Or it could simply be a reflection of the inordinate number of outdoor activities that exist in northern Arizona; even living in the area for 10+ years isn’t enough time to hit everything. Either way, after finally venturing into the Petrified Forest, I can emphatically say that it should be mentioned with the best that northern Arizona has to offer.
Located amongst the vast Painted Desert of northeastern Arizona, the main attraction of Petrified Forest is of course the petrified wood. The formation of petrified wood is initiated when downed trees are quickly buried by sediment. Once entombed in the sediment, the lack of oxygen prevents the logs from decaying as they normally would when exposed directly to the atmosphere. In this case, the logs (none of which remain standing, despite the name “Petrified Forest”) were likely brought here in massive logjams along an ancient river system that existed during the Triassic period. A combination of sediment from the river and ash from nearby volcanoes buried the logs, not to be seen again for more than 200 million years. During this time, as the logs became buried under an increasingly deep pile of overlying sediment, dissolved silica began to crystallize in the pore spaces of the wood as quartz, eventually replacing all of the organic material while maintaining the original shape and structure of the log.
A brilliantly colored petrified wood fragment.
Petrified wood is not particularly rare. Good examples abound in Yellowstone National Park, Washington state, Utah, Colorado, Oregon, Alberta, New Zealand…the list goes on and on. What makes Petrified Forest National Park unique is the quantities found here. Due to the aforementioned Triassic log jams, large quantities of wood were concentrated in small areas. In a location known today as Jasper Forest (see photos below), movement was not possible without walking over a nearly uniform carpeting of small petrified wood fragments and frequently having to clamber over 2-3 foot diameter logs. Truly stunning!
Petrified wood in the Jasper Forest, Petrified Forest National Park.
Overlooking the Jasper Forest at sunset.
Another unique aspect of Petrified Forest is the colorful canvas on which the wood is found. The wood is eroding out of a rock unit known as the Chinle Formation, which essentially consists of all of the river sediment and volcanic ash the buried the trees in the first place. More than 1000 feet thick in the park, the Chinle Formation is composed primarily of extremely soft mudstones, clays, and volcanic ash. Water is able to easily sculpt the soft rock into fantastically colored and oddly shaped badlands that make a spectacular backdrop for the logs.
The soft muds and clays of the Chinle Formation are easily eroded, forming badlands-like topography throughout the Painted Desert.
Colorful badlands in the Chinle Formation at Blue Mesa.
Petrified Forest National Park faces an issue not encountered by most other national parks, namely, the wholesale theft of the very resource it was established to protect. For this reason, the park is only open during daylight hours (from 8-5 in the winter) to minimize opportunities for looting. It strike me as very sad that such measures are necessary. With a little geological perspective, it becomes clear how incredibly lucky we are to experience a landscape like Petrified Forest at this moment in time. So easily eroded is the Chinle Formation that in many locations, several inches of it are removed each year. This may not sound like much, but geologically speaking, that’s a veritable bullet train of erosion. While it took tens of millions of years for the Chinle to be deposited, it will be erased from our planet by the unceasing forces of weathering and erosion in a tiny fraction of that. The petrified logs, being comprised mostly of silica, are harder and will last a little longer, but are still brittle and will eventually be washed into the Little Colorado River and swept downstream along with the colorful Chinle badlands.
What all this means is that the colorful Painted Desert/Petrified Forest landscape we see today is one that is extremely temporary. While this is true of most landscapes we see on Earth today—our planet likes to re-build, re-arrange, re-shape, and remove constantly—the Painted Desert is even more ephemeral than most. While mountain ranges comprised of harder, erosion-resistant granite or quartzite (like most of the Rockies) can stand the test of time to some degree, the longevity of the Painted Desert, its soft sediments, and its brittle petrified wood is comparatively brief. Stealing this treasured natural resource only abbreviates our time with the Petrified Forest even more.
Pieces of petrified wood accumulate in small hollows in the extensively gullied Chinle Formation.
The soft sediment surrounding the logs is easily transported away by small streams and washes.
Relatively hard chunks of petrified wood and quartz protect the softer sediment of the Chinle Formation from erosion, forming pedestals small…
…and large!
A Photographic Journey Down Chuckanut Drive
Chuckanut Drive, a.k.a. Washington State Route 11, is one of the premier attractions here on the extreme northwestern fringe of the U.S. “The Nut”, as I like to call it, winds for just over 21 miles between Bellingham and Burlington. Hemmed in by the Chuckanut Mountains to the east and numerous scenic bays, inlets, and islands on the west, it offers a stunning variety of scenery for such a short stretch of road. Chuckanut Drive has truly been a gift to me the last year and a half, because I can be cruising down it (well, as least what passes for “cruising” in a 16 year old Corolla…) and taking photos within 5 minutes of leaving my house. I’ve done this several times recently, now that the Sun is once again gracing us with its presence past 4pm.
Chuckanut Drive is chock full of destinations that make you feel further from civilization than you actually are, places that are perfect for occasions when time is in short supply. One of my favorite such spots is the beach walk at Chuckanut Bay. Fortunately for me, it also happens to be one of the closest, sitting just barely inside Bellingham city limits. Close enough for me to walk if I was feeling ambitious. Nearly inaccessible at high tide, once the water level drops a couple of feet, a few hundred yard stroll to the northwest shore of the bay puts you in the middle of spectacular and bizarre rock formations sculpted out of the Chuckanut Sandstone by freezing sea spray that accumulates along the margin of this sheltered cove. This is also a great place to see honeycomb weathering features along the shore, as is adjacent Teddy Bear Cove.
I’m not sure what sort of critter makes these little volcano-like structures, but they are all over the place at low tide in Chuckanut Bay, one of my favorite local spots for photography.
Some of the intriguing and bizarre rock formations along the Chuckanut Beach Walk.
Chuckanut Drive is heaven for the geologically inclined for a couple of reasons. For one, the road itself is built on layers of weak sandstone that slope precariously towards the sea. When it rains, water seeps into the spaces between the layers, dramatically decreasing something called the coefficient of static friction, which is normally responsible for keeping the rock intact. In other words, the water essentially lubricates the surface between rock layers, causing causing large chunks of the hillside to frequently slough off, making Chuckanut Drive one of the most landslide prone highways in the state. Last winter, it seemed like the road was closed at least every few weeks in order to repair large gashes in the pavement caused by falling boulders.
Two, the sandstone exposed here, a rock unit known as the Chuckanut Formation, is chock full of fossilized ferns, palm fronds, gingko leaves, wood, and bark, relics from a time when the Pacific Northwest was just as wet as today, but a whole lot warmer. An exposure of this same rock unit an hour to the east even turned up a footprint of a giant Eocene flightless bird a few years back, which is now on display at Western Washington University.
A few miles further south of Chuckanut Bay is Larrabee State Park, the first state park in Washington, whose landscapes and marine life I’ve documented previously and continues to be a favorite spot to catch the sunset:
The Sun dips behind the San Juan Islands as seen from Larrabee State Park.
- Winter brings frequent morning fog to the coast of NW Washington, but it usually starts to burn off around mid-day. 10 minutes after I took this photo, the fog was gone, replaced by sunshine and a clear blue sky.
Heading south from Larrabee State Park, the road becomes increasingly curvy and narrow as it clings to the hillside passing oyster bars, cascading waterfalls, and smattering of million-dollar homes. (You never actually drive along the coast proper, that route is reserved for the Burlington Northern Railroad, but the views are even better as a result.) Keep your eyes on the road and wait for one of the plethora of pull-offs where you can take it all in without running the risk of driving off a cliff.
A short but steep hike from near the route’s southern end puts one at Samish Overlook, which offers unparalleled views of the San Juan Islands, the Skagit River Valley, Olympic Mountains, and even Mt. Rainier on a clear day. On days when the winds are right, this is a launching point for local paragliders. It’s also a cool place to go during a foggy spell; at nearly 1300 feet above sea level, the Overlook sits above the fog deck most days making for spectacular sunsets and less than spectacular dark and foggy hikes back to your car.
A colorful winter sunset from Samish Overlook, nearly 1300 feet directly above Chuckanut Drive. The tops of a few of the San Juan Islands are visible protruding above the fog.
The last nine miles of the route angle away from the mountains and coast and traverse the flat lands and fields of the Skagit River Valley. But just a few miles west of the Drive, along Bayview-Edison Road, you’ll find the Padilla Bay National Estuarine Reserve, which operates an excellent interpretive center with exhibits about the coastal ecosystems of the Puget Sound area and a small aquarium. This is also a great place to spot a number of the bald eagles that visit the Skagit River Valley and surrounding area each winter to feast upon dying salmon. Padilla Bay (actually an estuary) is so shallow that at low tide, mudflats extend for hundreds of yards away from the coast.
Spring brings large quantities of nesting Bald Eagles to the Skagit River Valley. We saw four eagles within five minutes of exiting the car at the Padilla Bay Interpretive Center.
Ripples in the muck reflect a cold, windy, and colorful sunset out on the mudflats at Padilla Bay.
Eventually, Chuckanut Drive meets up with I-5 in Burlington, just a few miles north of the infamous I-5 bridge that collapsed into the Skagit River last year. From here it’s a quick 15-20 minutes drive back to Bellingham along the interstate. Or if you feel like braving that bridge, I hear there are a few good breweries in Mt. Vernon….
Honeycomb Weathering from the Desert to the Sea
Continuing on with our recent geological theme here at Pyroclastic Pixels (you’d almost think I was a geology grad student or something…), today we are going to take a look at one of the most picturesque geological curiosities you’ll ever find: honeycomb weathering, also frequently referred to as “tafoni”. Those two terms aren’t really exactly quite completely equivalent but we’re not going to journey down the nit-picky fork in the road today. Honeycomb weathering is pretty cool. About the only thing that would make it better is if the holes were actually filled with honey. That joke sounded way better in my head than it looks on the screen.
Honeycomb weathering in sandstone at Teddy Bear Cove, Chuckanut Bay, WA (all pictures are from this locality unless otherwise noted)
Specific geographic and geologic conditions are needed for honeycomb weathering to develop, yet these conditions can be satisfied in a variety of places, from the arid deserts of the American Southwest, to the storm-battered shores of the Pacific Ocean. Here in northwestern Washington State, honeycomb weathering occurs along the coast, along and just above the high tide mark, in areas where a rock unit known as the Chuckanut Formation is present. The pictures on this page were taken at Teddy Bear Cove, just south of Bellingham, WA, which has some of the most spectacular examples I’ve ever seen. The Chuckanut Formation, or “the Nut” as I like to call it when I’m feeling lazy, is a thick series of sandstones, conglomerates, and occasional coal seams that were deposited about 60 million years ago when NW Washington occupied a large basin at the foot of an ancient mountain range that occupied more or less the same space that the Modern Cascades now occupy.
There is a good reason that sandstone is one of the rock types most susceptible to this type of weathering. Sandstone is essentially composed of countless tiny, sand-sized particles of various minerals (mostly quartz and feldspar in the case of “the Nut”) which are held together by some sort of substance, known as cement, that “glues” them all together into a solid mass. In most sandstones, this substance is either calcium carbonate (CaCO3) or silica dioxide (SiO2), also known as quartz. Honeycomb weathering forms when salt-laden sea spray lands on the sandstone. As the salty sea water evaporates, tiny salt crystals form on the surface of the rock. The growth of these salt crystals on the surface of the rock physically separates the sand particles from the cement. Over time (a long time…), this creates a small depression in the rock. Once a small indentation forms, a positive feedback effect is created; the hole has a greater surface area than a flat surface and thus more rock is exposed to incoming sea spray. Sand grains are thus separated from the cement at a faster rate, thereby enlarging the hole. In some locations, you can actually see little piles of sand grains in the cavities, grains that were once part of the rock but have now been forcibly removed by the salt. I’ve found that this is most prevalent in areas just above the high tide line where wave action can’t wash the sand grains back out to sea.
But Zach, you say…how then does honeycomb weathering form in places like the desert Southwest where the closest thing to sea spray you’re going to find is mule deer pee? Ah…well I’m glad you asked. We often observe honeycomb weathering in sandstone in places such as Southern Utah that are far away from the sea. I had some difficulty finding a halfway decent picture of desert honeycomb weathering from my archives, but I was able to find one that I took in 2008 in Capitol Reef National Park (see below). If you want to see a lot better examples, just do a Google image search for “Utah tafoni”. While the exact cause may vary, and the individual pits tend to be larger, the process involved is essentially the same. We still need to find some way to separate our sand grains from the cement. Many washes in the southwest are dry for most of the year but are very rich in dissolved salts when they do flood. In desert environments, it’s no surprise then that we tend to find honeycomb weathering predominantly along dry stream beds and canyons. When a flood comes through, even though the water may not be as saline as the ocean, it is still salty enough to form small salt crystals when it evaporates, which it invariably does. In other locations, slightly acidic groundwater percolating through rocks can actually chemically dissolve calcium carbonate cement, leaving the sand grains with nothing to cling to.
Larger scale cavernous weathering features in Capitol Reef National Park, Utah
Hard as it might be for you to believe, this has been only a cursory explanation of the honeycomb weathering formation process. If your brain hasn’t begun to resemble honeycomb weathering by now and you are interested in the gritty details (perhaps you arrived here in the process of researching a paper or maybe you’re a geology nerd like me and just like knowing about such things), an excellent academic paper on the formation of honeycomb weathering can be found here. Regardless, your next step should be to pull out a geologic map, find the closest beach with some sandstone, pull your boots on and go find yourself some honeycomb weathering! Or you could always just look at the rest of these pictures I suppose…
Zach Schierl Photography 