PLUM ISLAND — Mother Nature plays her part, of course.
But those who have seen Plum Island's beaches and dunes morph for decades say it isn't just the winds of nor'easters, the waves of the Atlantic Ocean and the natural characteristics of a barrier island that account for the erosion seen in recent years.
Man — or at least some of his inventions — is also to blame, they say.
Many locals say the jetties, groins and dredging — or in recent years, the lack of it — of the Merrimack River have contributed to the massive erosion of certain sections of Plum Island's beaches.
Paul Ivaska, the chairman of Newbury's Beach Committee, said nature's role is clear, but humans also contribute.
"A good part of (the erosion) is Mother Nature. It is a barrier beach, and the sand shifts," he said. But "my understanding is that there needs to be repairs to the jetty that have not been done to keep the erosion down."
The south jetty, which runs off Plum Island, is partly collapsing. Some argue the jetty plays an important role in shaping Plum Island, in part because of the way it interacts with natural phenomenons.
Scientists say mighty tidal rivers such as the Merrimack create two phenomenons outside their mouths.
The first is a massive sand hump that forms several hundred yards out in the ocean, caused by sand coming down the river, tides pushing water up and down the river, and sand migrating along the coast. In Plum Island's case, the movement of the sand along the shore is further complicated because it is funneled off the ends of the jetties.
Extending southward off that sand hump is the second natural phenomenon, a series of "bars," basically sand humps that run roughly parallel to the shore, caused by currents and sand migration. At low tide, those bars can be clearly seen a couple of hundred yards off Plum Island, running about 2 miles long and ending just south of the Center.
Newbury Selectman Vincent Russo, one of the leaders in the charge to fix the south jetty, has argued that the south jetty's disrepair causes erosion on the beach. Water goes over and through the jetty, and then down the trough between the beach and the bars. The fast-moving water pulls sand off the beach, causing erosion, Russo and others argue.
The problem is exacerbated by the Army Corps' failure to dredge a channel. The sandbars create a wall-like chokepoint, they argue, forcing the river to push water over the jetties. A deep-dug channel, they say, would allow water to flow out more quickly.
Over the past few decades the channel had been redug about every three years, but it's been about six years since it was last dug.
Byron Matthews, the mayor of Newburyport from 1968 to 1977, said he has seen what a damaged and repaired jetty can do to the island's beaches.
During his time as mayor, Matthews said, the erosion at the center beach was about as bad — if not worse — than conditions now. He said he thinks the reason for much of the erosion then and now are the breaches and holes in the south jetty.
And part of the fix came in the form of rebuilding that massive stone structure, he said.
When there are holes and breaches in the jetty, Matthews and Ivaska both said, the conventional wisdom is that the current of the river breaks through at those places — instead of moving out farther into the ocean — and carves into the beaches.
As an example of this theory, Matthews points to his family's cabin on the beach.
He said before the jetty was fixed in the 1970s, the ocean's water was just 18 feet from the home at high tide. Throughout the years though, he said, both the beach and the dunes built up until at high water the ocean was 300 feet from the cabin.
"After we repaired the jetty, the beach front started to come back," he said.
But that started to change three years ago, Matthews said, when once again he started to notice the deterioration of the beach, the dunes and the grass.
He said he suspects it is because the jetty is once again in need of repair.
"The change has been significant in the past three years," he said.
Local elected leaders, especially Russo, have fought for years to get funding from the federal government to fix the jetty.
But officials, including Matthews, other locals and those at the Army Corps of Engineers, said Plum Island's needs are low on the list of priorities.
"It is a lot of work, but I don't know how else it is going to happen," Matthews said. "Every state along the Atlantic coast is having the same problem. You have to go to Washington. That is where you have to go. That is where they print the money.
"You go down there and make relationships."
Ivaska said, "It seems that we are having great difficulty from the federal government to fix this issue. Nothing seems to be happening."
Matthews said he thinks the situation is more dire now because Plum Island is such huge tax base for the coffers of Newburyport and Newbury, especially with the major investments in recent years.
"I think it is more serious right now than it ever could be," he said. "We need a real program, if you will, of putting sand back on that beach somehow. The problem today is that you have to get in line."
Ivaska said another problem could be the stone groins. There is a series of five — or a groin field — that starts on the beaches of the Parker River National Wildlife Refuge and goes north.
"There is some thought that that might be contributing to the erosion taking place right now," he said.
The groins, also massive stone structures, run perpendicular to the beach and the ocean. The purpose of the groins is to slow the movement of sand along the coastline. They work by preventing the waves from moving sand by trapping it and not allowing it to move.
But scientists, including Rebecca Haney of the state's Coastal Management Zone, say groins can often prevent erosion in one place but cause problem in others. The practice of building groins, in fact, is not used very often anymore, Haney said.
"By trapping sand in one location you can have effects on someone else, basically causing erosion," she said.
In the end, though, no matter if it is the jetties, the groins or the federal government fighting, Matthews said, it is Mother Nature that is in control.
"The tide and the way the ocean goes, it is like a bulldozer," he said. "I think it is going to be a constant battle. Like they say, you can't beat Mother Nature."