Exploring the Earth and Sky of the West

Science

(Petrified) Forests of Stone

Close-up of log of petrified wood
Close-up of log of petrified wood

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.

Brilliantly colored petrified wood fragment

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 wood in the Jasper Forest, Petrified Forest National Park.

Overlooking the Jasper Forest at sunset.

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.

Chinle badlands

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

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.

Petrified wood in the Chinle Formation

Pieces of petrified wood accumulate in small hollows in the extensively gullied Chinle Formation.

Petrified logs in a small wash

The soft sediment surrounding the logs is easily transported away by small streams and washes.

Petrified wood and quartz on pedestals

Relatively hard chunks of petrified wood and quartz protect the softer sediment of the Chinle Formation from erosion, forming pedestals small…

Large piece of petrified wood in pedestal.

…and large!

 


Capturing Cosmic Dust with a Camera: the Zodiacal Light

Cameras can be strange machines. We tend to think of cameras as devices that faithfully record the nature of the landscape around us, which they do…at least most of the time. When this paradigm does break down, it is usually because the camera has failed to record something important, something that made a moment or an experience worth remembering. Oftentimes when this happens, we become disappointed. How many times have you been scrolling through vacation photos and lamented at how poorly they turned out? Sometimes we even realize the limitations of the camera in the moment itself. Perhaps you’ve experienced something akin to standing on the rim of the Grand Canyon at sunset and becoming so resigned to the fact that no photograph will ever satisfactorily capture the grandeur in front of you that you begin to ponder the option of chucking your camera into the great chasm below.

On rare occasions though, the camera delights us by managing to capture even MORE than meets the eye. After returning from a recent camping trip to the San Juan Islands in northwest Washington, I was surprised to find an unexpected apparition in some of the long-exposure photographs I took from our campsite on the west coast of San Juan Island.

Getting to the San Juans is no easy task; it took me about 5 hours to get there, even though “there” is just 35 miles by air from my front doorstep. As a result, the islands can feel remote and isolated, but standing along the coast at night is a not so gentle reminder that you’re actually only about eight miles across the Haro Strait from Victoria, a metro area of more than 300,000 people. Taking advantage of a somewhat rare, perfectly clear Pacific Northwest evening, I took a series of 15 second exposures looking west across the strait which I composted into this 180 degree panorama:

SanJuanIsland_NightSky_Panorama

Click photo to embiggen!

The first thing you notice is the egregious light pollution from Victoria. Even the skyglow from Vancouver, five times further away but seven times more populous, is visible through the tress. Amongst all of the artificial light sources though, some natural ones still manage to shine through. The faint tendrils of the winter Milky Way just barely register on the camera’s sensor but the bright winter constellations of Orion, Canis Major, and Taurus forcefully punch their way through. If you look really closely, you’ll see a faint, slightly elongated, pale blue glow hiding in-between the lights of Victoria and Sidney. This is a phenomenon known as the zodiacal light, and it’s what took me by surprise when I started putting these images together. Here’s an annotated version to help you out:

SJI_Panorama_Annotated

See it? It’s a slightly different color than the light domes and isn’t as round and symmetrical as the light radiating from the cities, but rather looks squished and creeps upward into the sky at an angle. What really betrays the nature of this mysterious glow is its location: it coincides almost perfectly with the ecliptic, the plane of our solar system which is also the apparent path that the Sun, Moon, and planets follow as they move across the night sky.

What does this have to do with the zodiacal light? Well, it turns out that the plane of our solar system is home to lots and lots of dust. Not the dust made of dead skin cells and carpet fuzz you find around your house, but rather interplanetary dust particles made mostly of carbon, silicon, and oxygen. These dust particles are really small, on the order of 10 micrometers in diameter, about the size of a mold spore. The exact source of this dust is controversial; most of it is thought to be the result of collisions between comets and asteroids although some may be leftover from the formation of the solar system itself, tiny pieces of debris that never got incorporated into a planet. Regardless of where it cam from, the dust is really good at reflecting sunlight. Just after sunset (or just prior to sunrise), the angle between the Sun, dust, and Earth is such that the light reflected of the surfaces of the innumerable dust particles reaches our eyes (or cameras) here on Earth, giving rise to the zodiacal light.

When you consider how small the dust is (and that the dust particles are on average more than 2 miles apart from one another!), it’s not hard to understand why the zodiacal light is so faint and difficult to spot. Due to a quirk of celestial geometry, spring is a great time to observe it from the northern hemisphere, but even then spotting it with the naked eye requires extremely dark skies. The conditions in the San Juans, while darker than many spots in Western Washington, are far too light polluted. However, digital cameras are MUCH more sensitive to faint sources of light than the human eye. It’s actually rather common for a camera to detect things in the night sky that aren’t visible otherwise. On the night I saw the aurora borealis for the first time about a year and a half ago, its presence was first betrayed to me as a faint green glow hugging the horizon on my camera’s LCD screen, hours before it became bright enough to see with the naked eye. If not for my camera’s ability to detect it, I would have been fast asleep instead of standing in a marshy field near the Canadian border when the aurora dramatically brightened a few hours later and streamers began appearing all over the sky.

Have you ever captured anything on camera that you found surprising? Share your thoughts or stories in the comments below.


Snails of a Different Color

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Up until a few days ago, I would have felt extremely confident saying that I’ve seen more fossilized sea snails in my life than I have real ones. After all, teaching a lab that revolves around sedimentary rocks for two quarters will put one in close contact with more dead gastropods than one ever thought possible. And when you spend a lot of time staring at multi-million-year-old fossils, it’s often easy to forget that lots of the little buggers have closely related relatives still trolling the high seas today.DSC_8284Just a few of the many, many, MANY different colored and patterned varieties of nucella lamellosa, the Frilled Dogwinkle

A few days ago though, I stumbled upon a sea snail breeding ground of epic proportions at a place called Point Whitehorn Marine Reserve. I had gone there with the express purpose of looking at rocks and I remain convinced that the snails made their dramatic appearance in order to force me to confront the inherent irony in going to a marine reserve to look at rocks. Near the low-tide line, a couple of bright orange striped shells grabbed my attention, sticking out marine creamsicles amidst the backdrop of drab green algae and seaweed, dull brown barnacles, and grey sky reflected in the waves. I soon realized that I was surrounded (in a benign and not even remotely threatening way) by hundreds upon hundreds of sea snails exhibiting a dazzling array of different colors and patterns.

Now, my knowledge of sea snail taxonomy is limited, but it appears that despite the disparate appearance of these snails,¬† they are all part of the same species: nucella lamellosa, also known as the Frilled Dogwinkle or Frilled Whelk (if anyone has information to the contrary, please let me know). Most of the snails in these photos are smooth; they have lost their ridges or frills that normally run along the length of their shell. This is apparently a common fate of nucella lamellosa that choose to spend their lives in places like Pt. Whitehorn which experience very rough surf during the winter. The frills literally get worn away, not at all surprising when you consider that the shells are made out of calcium carbonate, a substance that in it’s crystalline form is only a we bit harder than drywall.

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Purple was the rarest color I encountered; orange, black, grey, and pure white seemed to be the most prevalent.

Many rocks were encrusted with dozens of the snails, varying in size from babies barely larger than a pea, to a few gargantuan snails nearly four inches long. This species hatches in late winter and early spring, so this is a good time to get a sneak peak at the next generation. A female sea snail can apparently lay thousands of eggs each year, although like most species who opt for quantity over quality when it comes to reproduction, only a small percentage survive to adulthood. In the case of nucella lamellosa, that number is estimated at a paltry 1%. Upon reading this, I realized in horror that the occasional sharp “crunch” heard from underneath my boots while I was taking these photographs was nothing other than the sound of my contribution to this rather depressing and morbid statistic. But with any luck, those shell fragments I (inadvertently) created will get weathered, transported, buried, and fossilized, eventually re-surfacing in the collection of some enterprising geologist a few million years from now, a fate that can only be described as THE ultimate honor for any ambitious gastropod.

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The only decent shot I got of the innards of these snails.

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A handful of the less gaudy looking but substantially larger snails. The largest one here is almost three inches long.

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A variety six-pack of nucella lamellosa munching on some barnacles.

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