The sudden appearance of two large, rusty and barnacle-encrusted World War II-era munitions on the beaches of Cape Hatteras, N.C., this summer have puzzled the area's park rangers and local historians.

"We haven't had these in the past," said Boone Vandzura, the chief ranger of Cape Hatteras National Seashore, a 70-mile stretch of sand and surf that spans from Bodie Island to the tiny hamlet of Ocracoke. Vandzura said he believed it had been more than a decade since an unexploded munition appeared on the Cape's shores.

But within a week this month, Vandzura received reports of two aging pieces of ordnance. The first — identified by the Navy as a World War II-era bomb — was called in on July 14, while the second, a M38A practice bomb, also from World War II, was found 12 miles south of the first find on July 18. In both instances, a Navy bomb disposal team from Explosive Ordnance Disposal Mobile Unit 2, drove down from Norfolk, Va., and got rid of the munitions.

The two bombs on Hatteras make up the entirety of the team's calls for unexploded munitions this year, said Lt. Kristi Fontenot, a spokeswoman for the unit. The detachment covers all of North Carolina and Virginia and averages about five calls a year, she said.

Joseph Schwarzer, director of the North Carolina Maritime Museum at Cape Hatteras, said he couldn't recall munitions appearing on shore since he started his tenure in 1995, let alone two within a week, nor could Dan Couch, a lifelong resident of Hatteras and historian who could only remember a local named Nacie Peele who had an unexploded shell on his porch and stories of shrimpers bringing up ordnance in their nets.

"It's not surprising though," Schwarzer said. Cape Hatteras, a piece of land that juts out into an important shipping lane, has been witness to a litany of historic events that have littered the surrounding seabed with tens of thousands of pounds of weapons, including Civil War cannon balls, German torpedoes and practice bombs leftover from World War II.

"If anything is surprising it's that they only found two," Schwarzer said. The question, he said, is what "natural phenomenon" brought them to the shore.

Peter Traykovski, a scientist at the Woods Hole Oceanographic Institute in Woods Hole, Mass., said that a team of researchers working with the U.S. Strategic Environmental Research and Development Program, is trying to figure that out.

"It's about the economics of a response," he said. "If we find that they are highly mobile then a larger, more expensive cleanup effort is required, and if the munitions are spreading everywhere it becomes a much bigger problem."

The coastal areas of the United States, including Hawaii and Alaska, are home to tens of millions of pounds of dumped munitions, said Niall Slowey, a professor at Texas A&M University who has more than a decade researching the topic. That number includes 30,000 tons of chemical agents like mustard, that were dumped following the World Wars.

Though the number seems huge, that's just what was recorded, Slowey said. He added that an unknown amount of ordnance was disposed of or dropped during training and wartime and never documented. That, plus the roughly 5,000 former military installations in the United States, 400 of which could have potentially contaminated areas, make the scope of the problem daunting.

Additionally, it is unclear what the environmental impact will be, if any, once large quantities of the weapons start to degrade and break apart. Within the last two decades the Pentagon has started to devote more resources to the issue. The Army Corps of Engineers has a number of ongoing projects as part of the "military munitions response program," which spans from Martha's Vineyard to Pearl Harbor.

Traykovski and his colleagues' five-year study has used dummy munitions, acoustic trackers and special buoys to understand the type of sea conditions that make the old shells move. Cape Hatteras, Traykovski said, with its shallow sand shoals and often violent waves, could be a place where bigger munitions might move around significantly in shallow water.

"If old munitions are going to show up anywhere, they are going to show up there," Traykovski said, referring to the newly formed Shelly Island off Cape Hatteras where one of the munitions was found earlier this month, "as it has the perfect catcher's mitt geometry, to catch objects migrating from both the north and west."

Stanley Riggs, a research professor at East Carolina University and a coastal and marine geologist said North Carolina's Outer Banks is one of the most dynamic coastlines in the world, with an abundance of debris on the seafloor that migrates with the currents and weather.

"It used to be our trash bin," Riggs said. "And the Cape Hatteras area is one of the highest energy and most active shorelines along the Atlantic margin with a lot of past maritime war activity."

Shells from the 1861 bombardment of Hatteras Inlet still come to the surface when boats dredge the ferry channel there, says Schwarzer. During World War II, more than 60 merchant ships were sunk by German submarines off the Hatteras coast in the first six months of 1942, littering the bottom with supplies, depth charges and American bombs targeting enemy ships. The Outer Banks and its coastal waters were also once home to World War II aerial target ranges that are still littered with old bombs.

"It's a geological process here. Things get uncovered, sometimes it's fossils, sometimes it's parts of shipwrecks and sometimes it's munitions," Schwarzer said.

Though many of the rusted artifacts of war look almost indistinguishable from other ocean debris, they still can be lethal - their explosive cores and chemicals safely encased in layers of steel. In 1965 a scallop trawler accidentally brought a live torpedo aboard off Hatteras, and when the crew attempted to free it, the underwater weapon exploded, killing all eight aboard. In 2004, a clam dredging company in New Jersey unearthed an artillery shell filled with mustard agent in its semisolid, tar-like form. Three bomb disposal technicians were injured trying to destroy the artifact.

Officials warn that if you encounter something you think might be an unexploded shell, you should not touch it. Instead, back away carefully, and call 911 to report it.

