One Night, One Year, 20,000 Years: How Pell Point's Shore Changes

Getting Ready for Storm Season in Pell Point

1Pell Point is a small town on a sandy stretch of the Atlantic coast. Its old lighthouse stands on a bluff of sand and gravel about 20 m high, and a long beach runs south to a tidal inlet, a gap where the ocean and the bay meet. Every spring, shoreline manager Abel Nakashima measures how far the lighthouse is from the edge of the bluff (Table 1). Ximena Holt's seventh-grade class used his records to help the town plan for storm season.

2In most years, waves at high tide nibble at the foot of the bluff, and small slumps of sand slide down its face. In the winter of 2020 to 2021, a strong storm struck at high tide. Overnight, waves undercut the foot of the bluff, and a long section of its edge collapsed onto the beach. Mr. Nakashima says that about 5 m of the bluff disappeared that one night.

3The beach changes on a yearly cycle, too. The class measured the width of the dry beach below the lighthouse every other month (Graph 1). Divers from the harbor found that a sandbar about 200 m offshore grows bigger in winter, when waves are taller and steeper, and shrinks in summer, when waves are gentler. Along this coast, most waves arrive from the northeast, and as they wash up the beach at an angle they nudge sand grains southward a little at a time. The inlet's channel has been moving south for decades (Table 2).

4Some evidence covers a much longer time. After big storms strip away sand, dark peat with old tree stumps shows up on the beach. Peat forms in marshes, behind the shore. Fishing boats have dragged up mammoth teeth from the sea floor 40 km offshore, where the water is now about 60 m deep. Scientists estimate that about 20,000 years ago, when huge ice sheets covered much of North America, sea level was about 120 m lower than today. As the ice melted, the sea rose and the shoreline moved inland.