In Ancient South Cape Beach Tree Stumps, Signposts Of Coastal Change
By: Elsa H. Partan
The geological future of Cape Cod is being revealed, and it is a startling sight.
According to geologist Christopher V. Maio, the dozen ancient juniper stumps that emerged from South Cape Beach after a northeaster in March 2010 tell the story of how land disappeared into the ocean and how it might disappear again. With sea level rising faster now than it was a century ago, these ghosts of forests past are a harbinger of the future, according to the scientist.
Mr. Maio is a coastal researcher at the Environmental, Earth and Ocean Sciences Department at University of Massachusetts Boston who is studying the stumps under Dr. Allen M. Gontz for his PhD dissertation in collaboration with Waquoit Bay National Estuarine Research Reserve, the Ocean Systems Group at Woods Hole Oceanographic Institution, and the Massachusetts Board of Underwater Archeological Resources. His work is expected to last two more years.
Approximately 50 people attended Mr. Maio’s talk at WBNERR last Thursday.
For the first time, Mr. Maio announced the age of the ancient stumps, based on recently completed carbon dating. The youngest stumps are at least 340 years old, while the oldest date back at least 1,210 years, he said. A forest grew on present-day South Cape Beach about the time that Bartholomew Gosnold named Cape Cod in 1602.
“It’s in your face,” Mr. Maio said. “There used to be a forest here 400 years ago. Now it’s underwater. Now it’s gone. This is what we have to face in the future.”
Just how fast Mashpee beaches and marshes will disappear is the topic of further research by Mr. Maio and others. One of his research objectives is to “provide insights into the future implications of sea level rise on the Waquoit area,” Mr. Maio said.
Between 1873 and 1993, sea level rise was about 1.7 millimeters per year around the world, according to data cited by Mr. Maio. Between 1993 and 2009, the rate increased to 3.26 millimeters per year. This may not seem like a lot, but it adds up, Mr. Maio said. By the year 2100, sea level is expected to rise between half a meter and one meter on the East Coast. Storms can also take large chunks of coastline at a time, speeding up the change.
Some ecological patterns are well understood. As marshes are inundated with high ocean water, they migrate landward, often bumping into forests. The trees in the forest, unable to withstand ocean water, die off. Forest migrates inland, as well. It is important that some land is left undeveloped so that marshes and forests have somewhere to go, Mr. Maio said. If the marshes disappear, shellfish and other species will disappear, too, he added.
“What you see today is not what you will see tomorrow,” Mr. Maio said. “We see the coastline changing. It is not permanent and we need to act accordingly.”
Part of Mr. Maio’s research is to develop a picture of what the Waquoit area looked like thousands of years ago. To do this, he uses a seismic system his team nicknamed The Boomer. The device blasts sound waves from the surface of the ocean into the water. The waves bounce back to a receiver at different rates depending on the hardness of the material below the ocean floor. A computer program generates a picture based on the data. Mr. Maio also pulled a ground penetrating radar system along the beach, the terrestrial equivalent of The Boomer.
“We surveyed the heck out of the forest site,” Mr. Maio said.
The results are preliminary, but they give a picture of what used to be there—a valley with a river flowing through, 6,000 to 10,000 years old.
“What we think we found here is a glacier outwash channel,” he said, pointing to a series of wavy lines, a cross-section of the coast. “It is flowing out through Waquoit Bay. There is a very deep channel that went out into the Vineyard Sound. This may be one of the main channels that carried glacial melt water to the sound.”
An 1846 map shows a much smaller tidal inlet near the place where the stumps emerged. The inlet no longer exists, but the ground-penetrating radar revealed its location buried beneath the beach.
Mr. Maio used another device, called a Geoprobe, to poke a hole 13 feet down into the beach. The resulting sample of rocks and sand also had a layer of black peat. Mr. Maio said he plans to carbon date that layer, which is likely the dirt belonging to the ancient forest. That will tell him how long it took for the forest to get submerged.
Mr. Maio’s research prompted questions about how towns like Mashpee should handle development along the shore.
George F. Green Jr., assistant director of the Mashpee Wampanoag Natural Resources Department, said after the talk that people should not build houses close to the water. He was speaking for himself and not for the tribe.
“We have to move back,” he said. “We can only defend so much. Mother Nature is going to do what she is going to do.”
Jetties and other seawalls will only work for a while, he said. “We have to violate environmental regulations to protect houses. How long before nature takes it all back?”
Exactly how fast the sea will rise is unknown, Mr. Maio said. But it is rising, and faster than in recent history. “A mitigation strategy only goes so far,” he said. “Living on Cape Cod, we need to adapt. We have to step back from the coastline.”
*Correction: This article has been changed to reflect the correct year of the storm that unveiled the tree stumps. The storm was in 2010, not 2009.