From Canada to Central America, the many grandeurs of
North America’s diverse topography star in a just-released
high-resolution map from NASA’s Shuttle Radar Topography
Mission (SRTM). But a relatively obscure feature, all but
hidden in the flat limestone plateau of Mexico’s Yucatan
Peninsula, is what emerges as the initial showstopper from
the mission’s first released continental data set.
The existence of the impact crater, Chicxulub, was first
proposed in 1980. In the 1990s, satellite data and ground
studies allowed it to gain prominence among most scientists
as the long sought-after “smoking gun” responsible for the
demise of the dinosaurs and more than 70 percent of Earth’s
living species 65 million years ago. The SRTM has provided
the most telling visible evidence to date of a 180-kilometer
(112-mile) wide, 900-meter (3,000-foot) deep impact crater,
the result of a collision with a giant comet or asteroid on
one of Earth’s all-time worst days.
The North America and Yucatan Peninsula images created from
the map are available on the JPL Planetary Photo journal at:
http://photojournal.jpl.nasa.gov/catalog/PIA03377
http://photojournal.jpl.nasa.gov/catalog/PIA03379
“This new, complete North American data set greatly expands
our topographic knowledge of Canada, southern Alaska and its
Aleutian Islands, Mexico and Central America,” said Dr.
Michael Kobrick, SRTM project scientist at NASA’s Jet
Propulsion Laboratory (JPL), Pasadena, Calif.
“There are spectacular features that pop out in these maps as
never before, and more subtle features, like Chicxulub,
become apparent for the first time. In fact, much of the
surface expression of Chicxulub is so subtle; if you walked
across it you probably wouldn’t notice it. That’s where the
view from space becomes invaluable, ” Kobrick said.
The Chicxulub data show a subtle, yet unmistakable,
topographic indication of the impact crater’s outer boundary:
a semicircular trough 3 to 5 meters (10 to 15 feet) deep and
5 kilometers (3 miles) wide. Scientists believe the impact,
centered off Yucatan’s coast in the Caribbean, disturbed the
subsurface rocks, making them unstable. The rocks were
subsequently buried by limestone sediments, which erode
easily. The crater rim’s instability caused the limestone to
fracture along the rim, forming the trough. In addition, the
collapse of numerous limestone caverns above the crater rim
resulted in an arcing chain of sinkholes, called cenotes,
that are visible as small, circular depressions.
Exactly how the Chicxulub impact caused Earth’s mass
extinctions is not known. Some scientists think it threw
massive quantities of dust into the atmosphere, blocking the
sun and stopping plants from growing. Others believe sulfur
released by the impact lead to global sulfuric acid clouds
that blocked the sun and also fell as acid rain. Another
possibility is global wildfires triggered by atmospheric
reentry of red-hot debris.
The remainder of the North American data paints a dynamic
portrait of a geologically complex continent. Active
structural deformations of Earth’s crust along and near the
Pacific/North American tectonic plate boundary create the
diverse topographic relief of the Pacific coast. Across the
Great Plains, erosional patterns dominate, with stream
channels surrounding and penetrating remnants of older smooth
slopes. In Canada and the northern U.S., evidence of glaciers
from the last ice age abounds.
In February, NASA finished processing the mission’s data and
delivered it to the National Imagery and Mapping Agency
(NIMA). More than eight terabytes of data recorded aboard the
Space Shuttle Endeavour were refined into 200 billion
research-quality measurements of Earth’s landforms. The NIMA
will perform additional data finishing and send it to the
U.S. Geological Survey’s Earth Resources Observation Systems
Data Center, Sioux Falls, S.D., for final archiving and
distribution. South America will be the next continental
dataset.
The SRTM, flown Feb. 11 to 22, 2000, made 3-D measurements of
the more than 80 percent of Earth’s landmass located between
60 degrees north and 56 degrees south of the equator; areas
home to nearly 95 percent of the world’s population. SRTM is
a cooperative project of NASA, NIMA, the Department of
Defense, the German and Italian space agencies. Fulfilling
part of NASA’s mission to understand and protect our home
planet, it is managed by JPL for NASA’s Earth Science
Enterprise, Washington. The California Institute of
Technology in Pasadena manages JPL for NASA.
For more information about SRTM on the Internet, visit:
