What is the Wilkes Land Mass Anomaly?
In 1962 gravitational and seismic features on the Wilkes Ice sheet in Antarctica recorded by the U.S Victoria Land Traverse (1959-60), led Richard A. Schmidt (Geophysical and Polar Research Center, University of ...
What is the Wilkes Land Mass Anomaly?
In 1962 gravitational and seismic features on the Wilkes Ice sheet in Antarctica recorded by the U.S Victoria Land Traverse (1959-60), led Richard A. Schmidt (Geophysical and Polar Research Center, University of Wisconsin) to postulate that there must be a meteorite crater beneath the ice.
The hypothesis was later published in detail by J. Weihaupt in 1976, which stated as evidence the large gravitational anomaly and land topography below the ice sheet.
The evidence available at the time led Weihaupt to surmised that the subglacial crater was 243 km in diameter with a minimum depth of 848 meters.
The original data has now been supplemented by data from airborne radio sound survey, airborne gravity survey, airborne magnetic survey and satellite remote sensing and in 2006
NASA’s GRACE satellite was able to identify a 300 km diameter “mass concentration” (mascon) within the center of a “ring like structure”.
The new data from GRACE allowed a team led by Ralph von Frese and Laramie Potts of Ohio State University to re-asses the dimensions of the proposed impact crater to between 480 and 510 km.
However due to the location being buried beneath many meters of ice, direct samples have not yet been taken to “prove” this is indeed an impact crater, and it has also been suggested that this might also be evidence of; a volcanic structure; an igneous intrusion; an ancient igneous diapir; a subglacial sedimentary basin; a glacially eroded subglacial valley; or a tectonic feature, however there is strong evidence that it is indeed an impact crater.
When was the Anomaly created?
Due to the fact that a typical mascon, on Earth, will dissipate over time it has been calculated that the structure must be less that 500 million years old. There is also evidence that the structure has been interrupted by a rift valley, created some 100 million years ago as Australia separated from the the super continent “Gondwana”.
Researchers therefore give give the impact structure an estimated creation time of between 500 and 100 million years ago.
Impact event extinctions?
During the same time frame of this potential impact on the other side of the planet (at the time) a massive volcanic event was creating what is now known as the “Siberian Traps”. These are a huge region of volcanic rock that was created by a massive eruption event that is thought to be the largest of its kind in the last 500 million years. It is now hypothesised that the two events may be linked.
That the shockwaves caused by the impact in Antarctica “literally” provided additional energy to the Earth's mantel to create a chain reaction of seismic events in the lithosphere. This “super” massive event continued to pour molten material from our planets mantel for close to a million years and is believed to be one of the one of the keys reasons as to why 250 million years ago 96% of all marine species and 70% of land vertebrates suffered a mass extinction. This is also the only known extinction event of insects (57% of all families and 83% of all genera) (Permian - Triassic extinction event).
It should be noted that at present this is a hypothetical link and that no ejection material has been recovered within Antarctica to physically associate the two events.
Chicxulub Crater.
Another massive impact crater, the Chicxulub Crater is now widely accepted as being the impact event that is responsible for the massive extinction event at the end of the Cretaceous period (the one that killed all the dinosaurs). Buried underneath the Yucatan peninsula in Mexico it is known to have been formed by a large asteroid / comet about 10 to 15 km in diameter striking the Earth approximately 65 million years ago. The crater however is tiny when compared to the Wilkes crater being 180 km in diameter and only 20 km in depth making it roughly a ¼ the dimensions of the Wilkes crater.
Comparing the ratios of impactor to impact crater size between the Wilkes Crater and the Chicxulub Crater , it would seem that the impact force could be found. The exact formula is much more complicated and due to the lack of physical evidence no one knows the impact force of the Wilkes meteor or the size and density of the impacting object..
It can be said to have been anywhere from 3 to 5 times greater than Chicxulub event, which delivered an estimated energy equivalent of 100
teratons of TNT
.
