The aftermath of Hurricane Sandy has been visually well-documented by news media and anyone with an iPhone and an Instagram or Twitter account. But what about the subterranean aftermath– the havoc wreaked in the tunnels of New York City’s mass transit systems ? For coverage of that destruction, the public has been turning to the Metropolitan Transit Authority’s very own Flickr photostream.

Even before Sandy touched ground, the MTA began posting Flickr photos of the agency’s storm preparation: a tubular dam inflated at the West Side Yard, walls of sandbags stacked at MTA HQ, Grand Central and Penn Station evacuated and desolate. The first storm image came from a traffic camera inside the Hugh L. Carey Tunnel (formerly Brooklyn-Battery Tunnel), which revealed a road flooded with water. Posted on Oct. 29, the day of the storm, the photo is grainy but instantly powerful–one of the first images to reveal that Sandy was more devastating than anyone anticipated. With more than 144,000 views, it is the MTA’s most popular Flickr photo.

Hugh L. Carey Tunnel

On Monday, the MTA released a batch of images showing workers pumping water from the 14th Street Tubes, which carry the L train below the East River. “There was a large amount of interest in the L train being restored, so that was one reason why we thought folks would be interested in seeing these images,” says MTA spokesman Aaron Donovan, who oversees the Flickr feed. Donovan dispatched the agency’s staff photographer of 12 years, Patrick Cashin, to document the operation.

Cashin entered the subway at the Bedford Avenue station of the L line, then hitched a ride on a work train. At the site, workers were waiting to turn on a generator that would allow the pumping to begin. As they waited, Cashin snapped a photo of three workers inside the pitch-black pump train–one of the rare occasions when he used his flash. “We were sitting in the dark and they were talking amongst themselves,” says Cashin. “I liked the red handles of the valves on the right, so I said, ‘Let me get a group shot.’” Once the pumping began, he negotiated his way around the cramped tunnel space for over an hour–Nikon D4 camera in one hand, camera bag in the other, flashlight in mouth–in search of vantage points that wouldn’t disrupt the work flow. He shot as many photos as possible, since low light requires low shutter speed, which results in many blurry shots. “You just hope for that right frame, where everything is sharp enough,” he says.

Lighting was a particular challenge, since the tunnel was darker than most subway tunnels Cashin has photographed–no electricity means no halogen lights to illuminate the work. Instead, he relied on flashlights and lights from the pump train. In one of his more eerie shots, two workers peer down the length of the tunnel, illuminating the floodwater with their flashlights.

To date, the MTA has posted nearly 600 photos from Hurricane Sandy, documenting everything from damage at the South Ferry station to the impressive transferring of A-train cars to the Rockaways via flatbed truck. The cars will provide temporary shuttle service in that hard-hit area.

Besides using Cashin’s shots, the MTA has also been crowdsourcing photos within the agency. The idea was conceived on the fly during last year’s Hurricane Irene. This time, as Sandy loomed, the agency made a concerted effort to encourage photo submissions from employees in the field–and so far it’s worked. One employee snapshot, a boat resting squarely on a Metro-North track, made the rounds on the Internet and is among the MTA’s most-viewed photos.