水中で錆びていく前に

真珠湾の底に沈んでいるUSSアリゾナは戦争の記念碑として残されています。しかし、この軍艦にはまだ燃料であるオイルが詰まれており、そして遺骨も残されています。ばらばらになっているところもあります。

この船体にどんどん錆が付着しており、時間が経つにつれ崩れていきます。問題はこれをどのように維持していくかです。船体に微電流を流すことも可能ですが、ばらばらの部分までは届かず、そして船体内部はどのようになっているか調査されていません。

今後このような戦争遺跡の保護が重要な研究対象となっていくのではないでしょうか？戦艦大和なども現在は水中に残っていますがどんどん崩れていくことは確実です。大きな遺跡は引き上げることは出来ないので現状をどのように保護するのか？水中考古学の重要な課題です。

By NED POTTER

Dec. 7, 2006 — After all these years, Franklin D. Roosevelt’s voice still echoes.

“Yesterday, Dec. 7, 1941, a date which will live in infamy….”

Today, Pearl Harbor is very, very different. People remark at how peaceful it seems. That is fitting, because a thousand men are still entombed in the wreck of the USS Arizona.

“My concern is that the ship lives as long as it can as an artifact of history,” says Daniel Martinez, a historian at the National Park Service.

But over time, that is becoming more and more difficult. Slowly, very slowly, the wreck of the Arizona is dissolving back into the sea.

500,000 Gallons of Oil

Steel plates, once an inch thick, have rusted down to less than half that. Tiny marine creatures have planted themselves on the ship’s hull and died there, creating a thick, concretelike coating that weighs it down.

And blobs of oil — so smooth they look like black pebbles — slowly float to the surface. There may still be half a million gallons onboard the Arizona; if the hull gives way, it will all escape.

When will that happen? It could begin in as little as a decade or two.

“As things corrode away, it’s going to reach a point where it cannot support its own weight, or the weight of what’s growing on it any longer, and it’s going to collapse into a debris pile,” says Timothy Foecke. He is a metallurgist at the National Institute of Standards and Technology in Gaithersburg, Md., and he’s been watching the ship from afar.

He and his team have done a computer model of the Arizona’s hull. It shows stresses building as the steel weakens and the concretion gets heavier.

Pieces of History

In his laboratory safe Foecke has rusty samples from the ship. He brings them out to show us.

“You get a little jolt when you’re holding a piece of the Arizona,” he says. “You realize that it was the single largest loss of life in the history of the Navy.

“We can keep it together for several more decades, but eventually it’s going to corrode away and become an iron-ore deposit, and that is just gravity and chemistry.”

In its time, the Arizona was a fearsome warship, 600 feet long. Its main guns — 14-inch cannons — could hit a target 20 miles away with 1,800-pound shells.

Today it lies in about 30 feet of water. The famous white memorial, built in 1962, stands on pylons, straddling its midsection.

“The ship has changed,” says Martinez, the Park Service historian. “The deterioration is progressive, but it’s throughout the exposed areas of the ship.”

No Simple Answers

But how to protect it? That is no simple matter. The Arizona is so important — as a symbol and final resting place for a thousand crewmen — that engineers cannot just prop up the hull, or drill holes to pump the oil out.

Divers regularly inspect the wreck. They send a small robot submarine inside. But out of respect for the dead, there are many areas they simply cannot reach.

Maybe — and it’s just an idea — they could run a mild electric current through the ship’s frame; that might counteract the chemical reactions that cause rust. But even that is complicated; the ship is in pieces, and because of the problems getting into it, the interior is incompletely mapped.

Martinez says he is optimistic.

“The Arizona is protected because we have a plan and a process for protecting that ship,” he says. “This deterioration that we’re looking at in the future is going to be watched.”

But even in such a quiet place, the years will do what they do. Waves and currents pull at the ship. The salt water changes the chemistry of the metal.

“She’s sitting in an environment that is going to be her ultimate demise,” says Jennifer Burbank, a Park Service diver, “and there’s nothing we can do about it.”

引用元：http://abcnews.go.com/Technology/story?id=2707972&page=1