Do fundo do mar... Sea bottom
Friday, December 17, 2004
Surf uncovers tracks laid in the 1700s
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Boston.com News
By Bill Sargent
December 14, 2004
Last month, a 100-foot strip of peat marsh appeared in the surf off Nauset Beach on Cape Cod. The peat had the hoof prints of oxen and horses and was crisscrossed with wagon tracks that looked like they had been laid down yesterday, though they probably date to the 1700s when the marsh and barrier beach were 800 feet farther out to sea.
This strip of living history is only the latest artifact to be unearthed by the rising ocean. Cape Cod's outer arm is receding at an average rate of 3 feet a year. This year, Nauset Beach lost 6 feet off the fragile dunes that protect its parking lot, less than a hundred feet away.
Waves, wind or particularly high tides are the usual suspects for any particular instance of erosion, but over the long term, it is sea-level rise caused by gradual global warming since the last ice age that is driving this rapid rate of change.
The rising ocean is now acting like a giant archeologist's trowel, inexorably unearthing Cape Cod's human artifacts by turning over the sand and pushing the barrier beach inland. In 1990, it was the remains of a prehistoric Native American Indian village uncovered on Coast Guard Beach in Eastham; in 1863, it was the wreck of the tall ship, Sparrowhawk.
The Sparrowhawk reveals how this erosion manifests itself. In 1626, the Sparrowhawk ran aground on the marshes of Pleasant Bay, protected behind Nauset Beach. The governor of the Massachusetts Bay Colony dutifully reported the details to London, and the wreck was then forgotten. During the intervening 237 years, Nauset Beach was pushed 800 feet westward, rolling over the sepulchral remains of the long forgotten wreck.
According to several coastal geologists, the same thing happened this autumn, unearthing tracks laid down between 200 and 250 years ago. Oxen, horse and wagon tracks left in the marsh were buried by sand during winter storms.
In the intervening years, Nauset Beach has rolled over, so the tracks appear incongruously on the ocean side of the barrier beach. Geologists calculated the dates the tracks were laid by comparing beach erosion known to have happened between the time the Sparrowhawk sank and was recovered.
Now that the tracks are exposed, they will probably wash away this winter, the scientists said.
Back when they were put down, most of the town's able-bodied men would be out on the marshes every summer cutting salt hay for their livestock. It was a grueling job. Clouds of mosquitoes and greenhead flies buzzed about the heads of the sweaty men and beasts. Sometimes the oxen were transported to the marshes on shallow draft boats; sometimes they fell into muddy slough ponds.
But the work was worth it. Before the advent of petroleum, having access to a salt marsh was like owning your own oil well. Hay fueled New England's local economies. It was fed to horses for transportation, to sheep for clothing, and to cattle for milk, meat and work. It was the salt hay marshes that convinced the Pilgrims to expand to Cape Cod in the 1600s, and, by the 1700s, Cape Cod and North Shore farmers were shipping hay to Boston to be sold to urbanites in Haymarket Square.
About 10,000 years ago, Cape Cod was a rough pile of rocks and gravel that extended 2 to 3 miles farther out to sea. But the glaciers had retreated, the planet was warming and the oceans were rising. About 2,000 years ago, Cape Cod looked somewhat like it does today, only the sea level was 6 feet lower. The outer arm of Cape Cod had attained its smooth and rounded shape, but Nauset Beach was almost a mile farther east.
By the time the wagon tracks were made, Nauset Beach protected a bay and marsh system that stretched from Eastham south to Chatham. Today that system has been separated into two distinct estuaries, Town Cove and Nauset inlet to the north and Pleasant Bay to the south.
According to Robert Oldale, a geologist with the US Geological Survey, Cape Cod will be almost gone in another 2,000 years at the present rate of sea-level rise. Most of the peninsula's highlands and bluffs will have washed away and its outer reaches will be 2 miles closer to the mainland.
In 5,000 years, all that will be left of Cape Cod is a long thin barrier beach like the present Nauset Beach. The beach will connect what had been Cape Cod to Nantucket, Nantucket to Martha's Vineyard, and the Vineyard to the mainland. The remains of Cape Cod will be a mature barrier beach system protecting thousands of acres of marsh grass, the way the Outer Banks protect the marshes and coasts of North Carolina.
Boston.com News
By Bill Sargent
December 14, 2004
Last month, a 100-foot strip of peat marsh appeared in the surf off Nauset Beach on Cape Cod. The peat had the hoof prints of oxen and horses and was crisscrossed with wagon tracks that looked like they had been laid down yesterday, though they probably date to the 1700s when the marsh and barrier beach were 800 feet farther out to sea.
This strip of living history is only the latest artifact to be unearthed by the rising ocean. Cape Cod's outer arm is receding at an average rate of 3 feet a year. This year, Nauset Beach lost 6 feet off the fragile dunes that protect its parking lot, less than a hundred feet away.
Waves, wind or particularly high tides are the usual suspects for any particular instance of erosion, but over the long term, it is sea-level rise caused by gradual global warming since the last ice age that is driving this rapid rate of change.
The rising ocean is now acting like a giant archeologist's trowel, inexorably unearthing Cape Cod's human artifacts by turning over the sand and pushing the barrier beach inland. In 1990, it was the remains of a prehistoric Native American Indian village uncovered on Coast Guard Beach in Eastham; in 1863, it was the wreck of the tall ship, Sparrowhawk.
The Sparrowhawk reveals how this erosion manifests itself. In 1626, the Sparrowhawk ran aground on the marshes of Pleasant Bay, protected behind Nauset Beach. The governor of the Massachusetts Bay Colony dutifully reported the details to London, and the wreck was then forgotten. During the intervening 237 years, Nauset Beach was pushed 800 feet westward, rolling over the sepulchral remains of the long forgotten wreck.
According to several coastal geologists, the same thing happened this autumn, unearthing tracks laid down between 200 and 250 years ago. Oxen, horse and wagon tracks left in the marsh were buried by sand during winter storms.
In the intervening years, Nauset Beach has rolled over, so the tracks appear incongruously on the ocean side of the barrier beach. Geologists calculated the dates the tracks were laid by comparing beach erosion known to have happened between the time the Sparrowhawk sank and was recovered.
Now that the tracks are exposed, they will probably wash away this winter, the scientists said.
Back when they were put down, most of the town's able-bodied men would be out on the marshes every summer cutting salt hay for their livestock. It was a grueling job. Clouds of mosquitoes and greenhead flies buzzed about the heads of the sweaty men and beasts. Sometimes the oxen were transported to the marshes on shallow draft boats; sometimes they fell into muddy slough ponds.
But the work was worth it. Before the advent of petroleum, having access to a salt marsh was like owning your own oil well. Hay fueled New England's local economies. It was fed to horses for transportation, to sheep for clothing, and to cattle for milk, meat and work. It was the salt hay marshes that convinced the Pilgrims to expand to Cape Cod in the 1600s, and, by the 1700s, Cape Cod and North Shore farmers were shipping hay to Boston to be sold to urbanites in Haymarket Square.
About 10,000 years ago, Cape Cod was a rough pile of rocks and gravel that extended 2 to 3 miles farther out to sea. But the glaciers had retreated, the planet was warming and the oceans were rising. About 2,000 years ago, Cape Cod looked somewhat like it does today, only the sea level was 6 feet lower. The outer arm of Cape Cod had attained its smooth and rounded shape, but Nauset Beach was almost a mile farther east.
By the time the wagon tracks were made, Nauset Beach protected a bay and marsh system that stretched from Eastham south to Chatham. Today that system has been separated into two distinct estuaries, Town Cove and Nauset inlet to the north and Pleasant Bay to the south.
According to Robert Oldale, a geologist with the US Geological Survey, Cape Cod will be almost gone in another 2,000 years at the present rate of sea-level rise. Most of the peninsula's highlands and bluffs will have washed away and its outer reaches will be 2 miles closer to the mainland.
In 5,000 years, all that will be left of Cape Cod is a long thin barrier beach like the present Nauset Beach. The beach will connect what had been Cape Cod to Nantucket, Nantucket to Martha's Vineyard, and the Vineyard to the mainland. The remains of Cape Cod will be a mature barrier beach system protecting thousands of acres of marsh grass, the way the Outer Banks protect the marshes and coasts of North Carolina.
