The extraordinary force of the typhoon’s winds shattered the coconut palm forests that line the steep, narrow valley that for years has churned out so much geothermal energy. Particularly near the ridgelines, mile after mile of trees have changed from green to brown since the winds tore loose virtually every frond. The winds then twisted and bent the usually resilient trunks until they snapped or burst.

Sheltered in the valley below, however, the homes of the site’s 795 workers seem to have fared surprisingly well, although one of the military barracks has lost much of its green, corrugated steel roof. Agnes de Jesus, the senior vice president for the environment at the Energy Development Corporation, which now owns the power plants, said that no one was killed or seriously injured at the plants during the typhoon, even as the storm surge on the opposite side of the island, 50 miles to the east, killed thousands in the coastal cities of Tacloban, Palo and Tanauan.

Responding to the Arab oil embargo of 1973, President Ferdinand E. Marcos began developing the field in the late 1970s with a small demonstration project. The goal from the start was not environmental, but nationalistic and economic: to reduce the Philippines’ dependence on imported energy and save money on fuel bills.

After the demonstration project proved successful, five large geothermal plants were built atop boreholes in the same valley here in the mid-1990s, each big enough even today to power the entire island. Each of the five was built by a different company, and then all five transferred them to a state-owned company.

The state-owned company subsequently privatized them and they became the Energy Development Corporation, a company listed seven years ago on the Philippine Stock Exchange.

The valley here differs from many geothermal sites around the world in that the underground rocks are hotter and what comes up through the boreholes is superpressurized water, not steam.

The underground water here is at a scalding 480 to 660 degrees Fahrenheit. Four of the power plants essentially rely on two steps: first they spin turbines using the tendency of water at such high temperatures to expand into steam, and then they spin further turbines as the steam cools. Finally, those four power plants were designed to condense the steam into water in steel-reinforced wooden cooling towers for reinjection into the ground.