History of the tunnels
The 1968 riots shut down the school for several days as student protestors forcibly occupied some of the campus buildings. The students made use of the tunnels to move from building to building and WKCR, the student radio station, tapped phone lines in the tunnels to keep tabs on the university and police response. Radical groups such as the SDS and some Harlem civil rights protestors also joined the protest making it very dangerous. The tunnels, which allowed the students to successfully occupy the buildings, were also their undoing, as university staff and eventually the police used them to capture and remove the protestors.
The protestors' use of the tunnels made Columbia realize they were a liability, prompting several tunnels to be walled off or locked. Tunnels locked/blocked in response to the 1968 riots include, but may not be limited to:
It is difficult to determine if a certain tunnel that was blocked was in response to the riots or Ken Hechtman's activities.