Soon after snow storms, mysterious swaths of green appear in the Yard, hinting of an entire world lurking beneath Harvard’s familiar landscape. There are 3.5 miles of tunnels running under this University, and the heat they radiate melts the snow above. Knowledge of the extensive tunnel system used to be more common, as students would regularly explore them. But, for the past few decades, Harvard’s underground world has remained hidden in the annals of Harvard lore.

Recently, tunnels have played a significant role in Harvard’s relationship with the city of Cambridge. Harvard decided to abandon its plans for a tunnel connecting the two government department buildings currently being constructed on either side of Cambridge Street just past the Graduate School of Design. This was a serious blow to the project, which depended on the tunnel as a means of moving both people and supplies safely under the street. Mid-Cambridge residents, who fought the tunnel with everything they had, not only lost out on some nice incentives that Harvard was offering, but also will now have to deal with people constantly crossing the street, which is both dangerous and annoying.

At this point, it’s not worth crying over the loss of a single tunnel, especially when Harvard already has so many of them. These tunnels extend from the Business School to the Law School, connecting dorm, lab and classroom buildings.

There are two main systems of tunnels—steam and food. The steam tunnels emanate from the Harvard-owned plant at the corner of Memorial Drive and Western Avenue (which I discussed in my last column). The food tunnels, comprising only a small percentage of the total, link a central kitchen on JFK Street with smaller “finishing kitchens” in most of the River houses. They are about 15 feet wide and are constantly traversed by battery-powered carts equipped with heated and cooled food containers.

The steam tunnels vary in size, but most are about eight feet high, eight feet wide, and situated six feet below the surface. Ten and 12 inch steam pipes run along each wall, their contents rushing along at around 400 degrees and 100 pounds of pressure. Four inches of insulation surround the pipes and, in conjunction with a ventilation system, maintain the tunnels at an acceptable temperature (although not a comfortable one, since workers often face 100 degree heat). In addition to steam pipes, numerous cables for internet and telephone pass through the tunnels, making them essential to the University’s daily operations.

One main break in the tunnel system occurs at Mass. Ave., where the distance between the Red Line and the street is just over three feet. At this point, the Harvard steam tunnel becomes extremely narrow—the pipes have no problem getting through, but humans are forced to lie down on carts and propel themselves using a pulley system.

Due to high temperature and pressure, the pipes are extremely dangerous and must be highly maintained and monitored at all times. A break in the steam pipes would kill anyone nearby in the tunnels. The main liability is at the expansion joints, special fittings that prevent the pipes from buckling when the steam is turned on and off. During this transition, the pipes can expand six to nine inches over a 300 foot distance.

Even though the maintenance of this system is high—a number of people work full time on it—it is still better than the alternatives. Mainly, it prevents a need for numerous boilers, freeing up a great deal of space in the houses and elsewhere (the Radcliffe yard and quadrangle have their own distinct boiler systems). Also, it allows for better environmental controls on a single fuel-burning source.

Despite being a below-ground phenomenon, the steam tunnels are the impetus for many above-ground constructions. The Weeks footbridge between Leverett and the B-School? It was built to carry the steam pipes when they were extended across the Charles in 1926; a three-foot high crawlspace allows workers to traverse the river inside the bridge. How about those weird mushroom things when you’re walking from the Yard to the Science Center? They let excess heat escape from the tunnels.

The tunnels have been used for more than just food and steam—moving important guests when the need has arisen. In 1968 Alabama Governor George C. Wallace escaped an angry crowd outside Sanders Theater by escaping through the tunnels. Henry A. Kissinger avoided anti-war protestors by leaving through the tunnels after a Vietnam-era speech.

In recent years, it has become a rarity to find students heading into the tunnels. There are hundreds of entrances, many of them through nondescript basement doors in the houses. However, all of the tunnel doors have been alarmed and linked to a central control room that is monitored 24-hours-a-day, making access difficult (not to mention criminal). But wandering the tunnels still seems like a worthwhile pursuit. I think I’ll give it a shot.

Zachary R. Heineman ’03 is a history and literature concentrator in Leverett House House. His column appears on alternate Mondays.