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August 16, 2018

Petrified

While the beauty and variety of trees to be found on Earth can quickly boggle the mind, some of the most interesting and mysterious are those that aren’t even alive today. No, we are not speaking of that tree on your property that recently died or was blown over in one of the South’s fearsome storms. These are trees that haven’t photosynthesized for millions of years. Keep readingto find out how a tree that old can not only be seen today, but give us clues about what the Earth was like thousands and millions of years ago.

On August 29, 1870, a young Army lieutenant by the name of Gustavus Doane clambered to the top of Mount Washburn above the Yellowstone River. Looking toward the south, he expected to see more mountains. What he was looking at, however, was the crater of an extinct volcano, 45 miles across, covered by a forest of trees. Doane figured out what he was looking at, but the only thing he had wrong was his thought that the volcano was extinct. It wasn’t then, and isn’t today. Yellowstone National Park sits on top of a volcanic “hot spot”: an up-welling of molten magma as shallow as 5-7 miles beneath the surface of the Earth. The Hawaiian Islands, whose volcanic mischief has been much in the news of late, sits over a similar hot spot in the Pacific Ocean. The difference between the two is that the upwelling lava in Hawaii is bubbling out at the surface, creating a pyroclastic flood of destruction and future beach-front property. At Yellowstone, water from rain and snow trickles deep into the ground, where the magma heats it to near boiling and vents it from a plethora of spouting, bubbling, steaming geysers, caves, and mud pots. The best known of these is that familiar intermittent geyser know as Old Faithful. It is not uncommon to see near boiling water flowing from a fissure and flowing into a clear, cold flowing mountain stream just a few feet away!

So, what of those mysterious trees mentioned earlier? These are the lesser known products of Yellowstone’s volcanic activity. The steaming, spouting, spewing of water and mud from the bowels of today’s Yellowstone is impressive, but minuscule volcanism compared to the cataclysmic eruptions that took place there before the dawn of man. The most recent occurred about 640,000 years ago and was 1000 times the size of the 1980 Mount St. Helens eruption in Washington State. The petrified trees of Yellowstone were stopped in their tracks during eruptions that took place during the Eocene Epoch, 50 million years ago, when ash and mud flows buried a number of trees on Specimen Ridge in the Lamar Valley region of the park. While such trees may be found in many localities on Earth, not as common is the way in which many of the fossilized trees here were preserved: STANDING! While it is commonly thought that the Specimen Ridge trees were actually growing in the spots where they are found today, the eruption of Mount St. Helens revealed that most of the trees there were blown away from their original locations. Trees that wound up floating in lakes became waterlogged and were floating vertically when they hit the bottom of the lake. Sediments from the volcanic action settled to the bottom around the bases of the trees and embedded them in an upright position. Other trees that had roots intact were weighted into the vertical position and similarly cemented into place. However it occurred, experiencing a tree still standing 50 million years after it stopped growing is awe-inspiring.

Petrifaction is a process that is not fully understood. What is known is that the volcanic ash that entombed the trees, or the water in the lakes where they sank, created an anaerobic, or oxygen-free environment, which is essential for the process to take place. If it were not for this, the trees would simply decay from the breakdown by microorganisms as they do in a living forest. The ash contained minerals such as silica which dissolved as water turned the ash to mud. The mineral-laden water would then either:

  • Infiltrate the cavities within and between the cells of the tree, while preserving all of the tree’s vegetable matter, OR
  • Completely replace the plant tissues, possibly after filling the voids in the tree as above.

Either way, the end product is the same: the wood is basically turned into stone. Look at the photos here and see the standing trees and stumps. The structure of the trees can readily be seen, including the trunks, root flares, root masses, annual rings, and rays, or bands of cells that run tangentially across the stem. The coloration commonly seen in petrified wood is caused by elements in the minerals: Iron (Fe) produces reds and yellows, while blues and greens come from Manganese (Mn) and Copper (Cu).

What is fairly well understood and even more amazing is what scientists have been able to learn from studying these trees. For example, their identity: most of the trees in the Lamar Valley are Redwood Trees (Sequoia magnifica). This is an extinct species related to the Coast Redwood of California (Sequoia sempervirens). Other names in this fossilized forest have familiar rings to them as well – Magnolia, Dogwood, Oak, Sycamore, and Chestnut. Familiar sounding to us possibly, but awfully foreign-sounding for a high-altitude plateau in northwestern Wyoming, where summer temperatures often exceed 100 degrees F and the bitterly cold winters can dish out sub-zero temperatures for extended periods of time. The nutrient poor soils of Yellowstone today also belie such a rich forest, where Lodgepole Pine have adapted to these conditions along with Whitebark Pine, whose nuts feed both Black and Grizzly Bears.

Even the Redwoods seem out of place. The Coast Redwoods of California grow in a much milder climate and attain their status as the world’s tallest trees as one result of a near constant supply of moisture by rainfall and coastal fog. The largest petrified stump in the photos is a Redwood tree, 26 feet in circumference at its base. This particular tree likely towered several hundred feet over the Lamar Valley. The story revealed to us by “forest misfits” is that the climate in Yellowstone was much milder and much wetter 50 million years ago than it is today.
Years before Gustavus Doane climbed to the top of Mount Washburn to survey the steaming landscape of Yellowstone, a crusty fur trapper by the name of Jim Bridger reconnoitered these parts in defiance of the Native American threat in the region, and the mystique brought about by the steaming volcanism of the land. Bridger was a legendary man but quite a spinner of tall tales. He once told an Army general: “Come with me to the Yellowstone…and I’ll show you peetrified trees a-growing, with peetrified birds on ‘em a-singing peetrified songs!”