Tuesday, May 1, 2012

Epilogue of Yellowstone

Yellowstone National Park contains world renowned: geothermal features, volcanic past, over 50 species of mammals, 311 recorded species of birds, and the devastating fire of 1988. Out of the 3 million visitors that travel to Yellowstone each year, many will leave the park without see the worlds largest aggregation of upright petrified trees, or the unique sedimentary rock formations of hoodoos. 


The two main attractions are:


Volcano activity

USGS Geologic Map of the lava flows overlaying with the faults.
Examples are: pumice breccia on Purple Mountain, Obsidian Cliff, Balsalt columns at Overhanging Cliff, tuff at Virginia Cascade (that is undergoing weathering!), and the famous caldera of Yellowstone.


Geothermal features
Diagram of the different types of geothermal features found in Yellowstone. Yellowstone is the most concentrated location of geothermal activity with 10,000 thermal features and 300 geysers!



Grand Canyon of Yellowstone is another main tourist attraction, with over eight different viewing spots along the Yellowstone River. The two major waterfalls are Lower Falls and Upper Falls. 
Aerial view of Upper and Lower Falls in 1974.
Yellowstone River contains: meandering channels, alluvial deposits, waterfalls, eroding bedrock, and knick points. This perennial river is part of a larger dendritic drainage pattern, starting in North Dakota. Observing the map of the drainage basin, there are three tributaries with Yellowstone River being the largest. 

Section of Missouri River Basin with Yellowstone River at the main tributary. Yellowstone National Park is highlighted in yellow.

Ten years from now Yellowstone River will continue eroding away the canyon, picking up the softer rhyolite in the dissolved and suspended load. Resistant rock, in this case hard rhyolite, will collapse as undercuts crave out the less resistant rock. Scientists speculate an ancient geyser basin is responsible for the softening of the rhyolite (chemical weathering), that in turn help create the waterfalls. Both Upper and Lower Falls will retreat upstream, showing the knick points are temporary. Yellowstone River occupies a V-shaped valley, exposing the process of fluvial erosion and perhaps a flood by glacial dam breaking over 14,000 years ago.



Yellostone's 1988 fire that destroyed one-third of Yellowstone could happen again in a hundred years! 
Over 25,000 firefighters participated to control the flames that lasted from early July to October in 1988.

The likelihood that a fire of the 1988's size will happen now is slim. There is still vegetation growing, and not the quantities that it needs to start, and maintain a fire of that magnitude. Majority of Yellowstone, eighty percent, is composed of forest. Lodgepole pine make up the forests. These trees have brittle needles due to the less around of precipitation; retaining as much moisture as possible.  The soil of Yellowstone is mostly weathered rhyolite bedrock formed from lava flows that filled the caldera. New vegetation in an arid landscape, pine trees, soil that wicks away moisture is a great recipe for a wild fire. 


Rhyolite is the main soil at Yellowstone, exposing Yellowstone's violent past.
Rhyolite is not permeable and a low nutrient content. Geoscientists studying sediment cores say fires have increased in frequency over the past 9,000 years, compared to the collection of over 17,000 year history. If the carbon dioxide continues to increase in our ozone, causing temperatures to rise, we may see more frequent fires in Yellowstone. Vistors here in 1988 are taking photos of the recent fire. Evidence from the petrified forests (chemical weathering by concentrated silica in the groundwater.) in Yellowstone are dated back to the Eocene period. Where the climate was around 7-12 degrees warmer than it is today. Scientists discovered the petrified trees were types that require wetter and warmer climate. Examples of petrified trees in Yellowstone are: Chestnut, Magnolia, Sycamore and Willow. Evidence that vegetation will thrive with several decades of uninterrupted growth (currently happening) and wet years (what the climate may be in 100 years) a massive fire may burn Yellowstone again.

Satellite image of Yellowstone's 1988 fire.




Rhyolite magma is moving upward towards to two domes. 
In a thousand years, the two resurgent domes in Yellowstone will have grown to concerning levels. As my previous blog discussed, earthquake swarms can have up to two thousand earthquakes in a span of four months! Faults can generate earthquakes, which there are many faults around the caldera. Earthquakes can: create geothermal explosions, cause debris flows, flooding, and damage roads. Importantly, earthquakes trigger compression of the plates near the fault lines, increasing the size of the resurgent domes. 


Looking northwest Mallard Lake Dome and the gaben that formed along its axis.
760,00 years passed between the first super-eurption to the second one, and 650,000 years passed since the second, and third eruption. It has been 640,000 years since the last Yellowstone eruption. Scientists hypothesize that we are owe for our next big eruption. Yet, Yellowstone's hot spot is continuing to move underneath the North American Plate traveling southwestward, perhaps changing the future of Yellowstone next eruption!


Generalized cross section of the crust underYellowstone. Expressing the ring faults where a lot of the earthquakes and growth of the domes occur.





One key factor in the future of Yellowstone are the tourists. Yellowstone is a hot spot for vacations. People bring in pollution, trash, food and congestion to the once mysterious place. The interaction between the wildlife and visitors have transformed over the century. So will the geology and the physical geography of Yellowstone National Park!


My Ma, and I depressed at the Leaving Yellowstone National Park sign.




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