Laser Scans Reveal Lost Civil War Tunnels Beneath Alcatraz

The remains of the hidden military structures were just a few centimeters beneath the surface.

Alcatraz prison has a long and infamous history. The penitentiary once housed some of the most notorious criminals such as Al Capone.

Today it is a popular tourist attraction. Now, some new findings are bound to make it even more so. High-tech radar and laser scans have uncovered lost civil war tunnels underneath the building.

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Just a few centimeters beneath the surface

“I was surprised for several reasons,” said Binghamton University archaeologist Timothy de Smet. “The remains of these historical archaeology features were just a few centimeters beneath the surface and they were miraculously and impeccably preserved. The concrete veneer of the Recreation Yard floor is incredibly thin and, in fact, in places sitting directly atop the architecture from the 1860s."

The researchers were able to make the discovery of the fragile remains because instead of digging, they use terrestrial laser scans, ground-penetrating radar data, and georectifications. Georectification is a process of looking at maps and referencing them to a spatial grid.

In essence, they compared what they found with their technology to what was on old maps. This nondestructive research method revealed the remnants of a buried 19th century hidden traverse beneath Alcatraz's recreation yard.

De Smet said the hidden military structures were in surprisingly good condition. "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. It was wonderful to find the history just beneath our feet that we can visualize for the public.”

Coastal fortification

Alcatraz’s military role as a 19th century coastal fortification is often overlooked but it is an important one. 

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“During the construction of the now-infamous Alcatraz prison in the early 1900s, there was only one regulation and protection of cultural heritage in the US: the American Antiquities Act of 1906. And even so, Alcatraz would not have been considered under it, as it was so young and seemingly insignificant,” said de Smet.

“As such, the area was essentially bulldozed from the former military installation to the modern prison we see today. In converting the area to a prison, the vast majority of the previous military history of the island had been erased, but we wondered if perhaps something of that significant time in both the islands and American history remained, but buried and preserved beneath the subsurface."

Using this novel noninvasive process allowed the researchers to find accurate spatial identification of these architectural structures depicted in historical documents without damaging them. Now, de Smet is arguing the technology can be used to safely study other important cultural and historic landmarks.

“With modern remote sensing methods like these, we can answer fundamental archaeological research questions about human behavior, social organization and cultural change through time without costly and destructive excavation, thereby preserving these non-renewable archaeological resources in the ground - or in situ as we say in the field - for future generations,” he said. 

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