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12 October 2011

Old Volcano, Older Footprints


(Click on image for larger view.)

Aniakchak National Monument and Preserve derives its name from a 6-mile (10-kilometer) caldera that sits midway down the Alaskan Peninsula. Geographers had noticed the circular feature more than a century ago, but it took a 1922 geologic expedition to confirm up close the origin of the depression. Several decades later, paleontologists made another find at Aniakchak: Dinosaurs once lived in the area, and some of their fossilized tracks remain.
Aniakchak is one of 232 American parks preserving fossils. The National Park Service provides information on these natural relicts as part of its celebration of National Fossil Day on October 12 and of Earth Science Week.
The Enhanced Thematic Mapper Plus on the Landsat 7 satellite captured the natural-color image above of Aniakchak National Monument and Preserve on September 15, 2000. The caldera dominates the view, and the southern rim casts a blue-gray shadow on nearby snow and ice on the slopes. (Because of the angle of sunlight, this image may cause the optical illusion known as relief inversion.) A lake lies near the caldera’s northeastern margin. Vegetation is scarce immediately around the caldera, but slopes are green farther away.
The caldera formed about 3,500 years ago when an explosive eruption blew away roughly 3,000 feet (1,000 meters) of overlying mountain. More recent seismic activity has pockmarked the caldera with cinder cones and lava flows.
The dinosaur tracks in Aniakchak are far older than the crater. They were left by plant-eating, bird-hipped dinosaurs about 70 million years ago. Anthony Fiorillo, based at the Museum of Nature and Science in Dallas, discovered the tracks and formally described them in 2004. Left by hadrosaurs, the tracks consist of smaller handprints and larger footprints.
Most people think of dinosaurs living in tropical, or at least temperate, environments, not at high latitudes such as Alaska. So how could dinosaurs thrive so far north?
Plate tectonic theory indicates that some lands that are now situated at high latitudes once rested nearer to the equator in our planet’s distant past. So one possible explanation for the dinosaur tracks is that it wasn’t in the same place. But by the time dinosaurs left their tracks in Aniakchak National Monument, North America was more or less in its present location. Detailed studies of rock layers from the region indicate that the Aniakchak area was at about the same latitude 70 million years ago.
Though Aniakchak was in roughly the same place, it doesn’t necessarily mean that it had the same climate. In fact, global climate about 70 million years ago was significantly warmer than today. So dinosaurs did not likely have to endure frigid temperatures common now, although they did experience some cold conditions and possibly snow. Regardless of temperatures, dinosaurs at high latitudes had to cope with prolonged periods of darkness during the winter. At Aniakchak (almost 57 degrees north) in the depth of winter, nighttime lasts nearly 18 hours.
  1. References

  2. Astronomy Education at the University of Nebraska-Lincoln. Daylight Hours Explorer. Accessed September 26, 2011.
  3. Fiorillo, A.R., Parrish, J.T. (2004). The first record of a Cretaceous dinosaur from southwestern Alaska. Cretaceous Research, 25(4), 453–458.
  4. Integrating Research and Education. (2011, August 31). Cretaceous Climate. Carleton College. Accessed September 24, 2011.
  5. NOVA. (2011, July 27). Arctic Dinosaurs. Accessed September 24, 2011.
  6. U.S. National Park Service. (2001). A Hadrosaur in Aniakchak National Monument. Accessed September 24, 2011.
  7. U.S. National Park Service. (2011, March 21). Aniakchak National Monument and Preserve. Accessed September 24, 2011.
  8. U.S. National Park Service. (2011, September 23). National Fossil Day. Accessed September 24, 2011.
NASA Earth Observatory image created by Jesse Allen and Robert Simmon, using Landsat data provided by the United States Geological Survey. Caption by Michon Scott.
Instrument: 
Landsat 7 - ETM+ - NASA