the Impact Site
These findings led
to an extensive search for a large impact crater that is 65 million years
old. Seven researchers finally located the impact site on Mexico's Yucatan
It is a huge buried
impact crater that is called Chicxulub, a Maya word that roughly translates
as "tail of the devil." The crater, now buried beneath a kilometer-thick
sequence of sediments, has been imaged using geophysical techniques that
allow us to visualize underground structures. It appears to have a diameter
of 145 to 180 km, which makes it one of the largest confirmed impact structures
on Earth. Only Sudbury in Canada and the Vredefort structure in South Africa
could potentially be larger.
paleogeographic reconstruction of the continents 65 Ma showing the impact
location in red
modern continents then submerged in light blue.
The asteroid or
comet that produced the Chicxulub crater was roughly 10 km in diameter.
When an object that size hits Earth's surface, it causes a tremendous shock
wave while transferring energy and momentum to the ground. The impact was
similar to a large explosion, although the energy of the Chicxulub impact
dwarfs anything modern civilization has experienced. The energy of the
impact was comparable to 100 million megatons of TNT, 6 million times more
energetic than the 1980 Mount St. Helens volcanic eruption. The impact
ejected rock from several kilometers beneath the surface of the Earth and
carved out a bowl-shaped crater nearly 100 km in diameter. In addition,
the shock of the impact produced magnitude-10 earthquakes, which were greater
than the magnitude of any we have ever measured in modern times.
The initial bowl-shaped
crater was very unstable, and its walls quickly collapsed along a series
of faults that enlarged the final diameter to between 145 and 180 km.
At the same time, the rock that had been compressed beneath the crater
by the impact rebounded, producing a peak-ring structure in the crater's
center. These dramatic changes, which rapidly transported huge volumes
of rock over distances of tens of kilometers, occurred within only a few
Because the impact
site was in a shallow sea, water rushed in to fill the circular depression.
Kilometer high waterfalls tumbled over the rim of the crater and roared
furiously across the floor of the crater.
filled and covered the crater, sediment on the bottom of the sea soon buried
the impact scar. The crater is no longer visible today, even when
standing directly over it.
In more recent times,
the impact crater has affected the circulation of groundwater on the Yucatan
Peninsula. This groundwater, has in some areas, dissolved the limestone
in the Yucatan peninsula. Below ground, this has produced caves.
At the surface, this has produced cenotes which are groundwater springs.
The cenotes form a ring, like a blue pearl necklace, that is nearly
coincident with the rim of the Chicxulub structure and is the only visible
feature on the surface to indicate a huge crater lurks below.
Map of Cenotes on the Yucatan Peninsula
The blue dots
show the locations of cenotes (groundwater springs) on the Yucatan peninsula.
The outline of
the cenotes ring is nearly coincident with the rim of the impact structure.
Figure 1, P.K.H. Maguire et al. in Meteorites: Flux with Time
and Impact Effects (1998).
The explosion that
produced the Chicxulub crater excavated a huge amount of material, which
was then ejected upwards. Most of the debris was deposited as a blanket
of material that covered North America and possible South America.
Near the impact crater the debris is tens to hundreds of meters thick,
while as far away as Colorado (over 2000 km distance), the debris is still
a centimeter thick (see photograph below). Additional material was
lofted in an expanding, vapor-rich plume that included gas from the vaporized
asteroid or comet. This plume rose far above the Earth's atmosphere,
enveloping it, and eventually depositing a thin layer of debris around
the entire world.
the K/T boundary sequence at Raton Basin in Colorado. The light gray unit
in the middle of the photograph (marked with the red knife) is composed
of two layers that mark the K-T boundary. A coal deposited in the Tertiary
Period, after dinosaurs disappeared, is deposited on top of the K-T boundary
Diagram of the
Raton Basin as it appeared before the impact event. The mudstone and siltstone
at the bottom of the above Raton Basin photograph were deposited in an
environment such as this.
Pillmore et al. in GSA Field Guide 1999.
This web site is part of the
NASA/UA Space Imagery Center's Impact Cratering Series.
Concept and content by David
Design, graphics, and images
by Jake Bailey and David A. Kring.
All information and images
are the property of the Space Imagery Center.
To obtain usage permission,
contact the Data Manager - Maria Schuchardt at firstname.lastname@example.org.