Five years ago today, an oil rig operated on behalf of the BP oil company exploded off Louisiana’s coast, killing 11 workers and creating a leak that dumped millions of gallons of oil into the Gulf of Mexico over 87 days.

Today’s anniversary is an occasion to hope that the BP tragedy won’t be forgotten, but the painful truth is that for much of the country — and even for many people in Louisiana — the accident is already a dim presence, if it even registers at all.

Living in the past isn’t healthy, and any healing process involves letting some memories fade. But some lessons of history should remain indelible. The abiding legacy of the BP disaster should be a clear and enduring awareness that the coastal ecology of Louisiana is fragile, its viability vulnerable to the hand of man.

That vulnerability was vividly documented five years ago, as hundreds of journalists from around the world gathered to tell millions of readers, listeners and viewers about the oil-blackened Gulf. The cameras are gone now, a testament to the fact that the passage of five years, measured in news cycles, is as remote as the prehistoric era that produced the oil in the first place.

The international media was drawn to the BP story, of course, because of the pictures — the fiery remains of a charred rig, those endless images of a darkening sea, and birds, blackened by pollution, struggling to keep alive. What was less visible to the cameras was the biggest tragedy of all — the horror of 11 lives extinguished in an instant, never to return.

In the cool light of hindsight, we can now understand something else this tragedy was teaching us, that the deepest wounds are not always the easiest ones to see. That is true enough of the broader and continuing catastrophe beyond the BP explosion — namely, the disappearance of the very coast that served as the backdrop for this mishap.

Coastal erosion, a complicated result of bad development policies and environmental abuses by industry, is a huge problem that doesn’t grab much attention beyond Louisiana because its workings are so gradual.

On this fifth anniversary of the BP explosion, we should recommit ourselves not only to saving the coast from future spills but keeping the coast itself from oblivion.