Military Traverse Underneath Alcatraz


BY STEPHANIE VALERA 03.01.2019






Aerial photograph (dated 1930s) of the Alcatraz island and penitentiary in the San Francisco Bay. (Photo Credit: OFF / AFP / Getty Images)


Alcatraz holds many forgotten secrets, but one has been discovered: High-tech radar and laser scans have uncovered a hidden military traverse underneath the infamous penitentiary, according to new research.


A team of researchers from Binghamton University, State University of New York used terrestrial laser scans, ground-penetrating radar data, and georectifications (the process of taking old digitized maps and linking them to a coordinate system so that they can be accurately geolocated in 3D space) to locate and assess the historical remains beneath the former recreation yard of the Alcatraz penitentiary, according to a press release.


The scans revealed that remnants of buried structures, including a “bombproof” earthwork traverse along with its underlying vaulted brick masonry tunnel and ventilation ducts, ran east to west beneath the recreation yard of the Alcatraz penitentiary, which is located in the San Francisco Bay, 1.25 miles offshore from San Francisco, Calif.

Binghamton University archaeologist Timothy de Smet, whose team’s findings are detailed in a paper published in the journal Near Surface Geophysics, said he was shocked to discover that the historical structures were maintained in such good condition.

“The remains of these historical archaeology features were just a few centimeters beneath the surface and they were miraculously and impeccably preserved,” de Smet said. “The concrete veneer of the Recreation Yard floor is incredibly thin and, in fact, in places sitting directly atop the architecture from the 1860s. We also learned that some of the earthwork traverses were covered over with thin concrete layers through time, likely to decrease erosion on the rainy windy island.”

Known as a former high-security federal penitentiary that once housed many of America’s most notorious gangsters and criminals, such as Al Capone, Alcatraz Island is now a National Historic Landmark that attracts several tourists in its location adjacent to the Golden Gate Bridge.

However, many overlook Alcatraz’s former military role as a 19th century coastal fortification, featuring underground ammunition. Since it was converted to a prison, researchers have been interested to see if there were any historical remains left of the fortification.





Binghamton University archaeologist Timothy de Smet and colleagues used terrestrial laser scans, ground-penetrating radar data and georectifications to locate and assess historical remains beneath the Alcatraz Federal Penitentiary. (Photo Credit: Timothy de Smet)


According to de Smet, during the construction of the Alcatraz prison in the 1900s, the area was essentially bulldozed from the former military installation to the modern prison we see today.


“We sought non-invasive, non-destructive means to ascertain if any historic archaeological remains lay beneath several parts of the island, like the Recreation Yard of the infamous US Federal penitentiary,” said de Smet. “We did not know what to expect. We did not know if there would be any extant subsurface architecture of these historically significant remains, or if there was anything left, what their extent and integrity would be like.”


The noninvasive process used by researchers permits accurate spatial identification 19th-century architectural structures depicted in historical documents. And this groundbreaking approach can also be applied to investigate other important cultural landmarks worldwide.


de Smet said the results prove that archaeologists can detect historical structures in a gentler manner: “These results are significant in that they show how modern technology can be used to answer fundamental questions of archaeological importance without any destructive excavations. This research shows that best practice approaches can be used to non-invasively non-destructively investigate the archaeological record with remote sensing alone.”