Calling card of catastrophe. Scanning electron microscope images show fibers and rods from fiberglass and drywall (top row) that are absent in regular Hudson River sediments (bottom row).

The Geological Legacy of 9-11

The collapse of the World Trade Center towers left a scar on the New York City skyline. Now it seems it may have left an indelible impression on New York Harbor as well. Researchers studying sediments in the Hudson River have found a distinct layer of ash from the collapse that will likely linger for centuries and may become a permanent part of the geologic record.

Geochemist Sarah Oktay of the University of Massachusetts, Boston, led a team of scientists that studied sediments in the Hudson River Estuary 1 month after the attack on the World Trade Center. The team found a layer of sediment a few millimeters thick that had elevated levels of copper and zinc and other elements. Using a scanning electron microscope, they saw silicon rods and fibers in the ash that probably came from fiberglass insulation as well as calcium that is typical of the gypsum in drywall. Most of the ash also had a ratio of strontium isotopes matching that of drywall, the team reports in the January issue of EOS Transactions.

The study also suggests that the sediment from the towers will stick around. While most estuaries collect sediment slowly--less than 2 centimeters per year--Oktay's team found that New York Harbor collects 5 or more centimeters a year. Because sediment builds up so fast, the layer of World Trade Center ash will be buried quickly, Oktay says, keeping it from being disturbed by bottom-dwelling creatures. Although some of the layer will probably be dredged from the harbor, other sections will remain buried in quieter areas.

The high sedimentation rate is likely to preserve the ash layer for centuries, agrees Peter Santschi, a geochemical oceanographer at Texas A&M University in Galveston. And it's even possible that the fingerprint of the collapse will be discernable a million years from now, he says, but that's far from certain. "It may not be likely given the regular climate changes that will happen in the future." Erosion caused by rising and falling sea levels could obliterate the record in many places, Santschi says.

Related sites
Environmental, Coastal and Ocean Sciences at the University of Massachusetts, Boston
Peter Santschi's research
USGS Environmental Studies of the World Trade Center area after 11 September 2001