Vi Patek came away from the Northeastern University Marine Science Center's opening lecture on Tuesday with a greater understanding of how beaches come and go.
The Nahant resident was intrigued by how tides and waves exert different forces on barrier beaches.
Where waves have the upper hand unbroken lengths of barrier islands stand.
Where tides exert the greatest force, inlets form, breaking barrier beaches into chains of islands.
Vi and 34 other audience members also heard Salem State geology professor Lindey Hanson describe how glaciers and rivers and homes and causeways have formed and changed beaches and barrier islands.
Two photographs of Marblehead's Devereux Beach looking toward Ledys Cove illustrated one of her points.
In the older photograph, that predates the Ocean Avenue causeway, the beach's elevation is much lower.
That's because the construction of the causeway has resulted in sand and rock being deposited on Devereux, elevating it considerably.
And speaking of elevation, the sea level of New England is rising, the professor said.
For barrier beaches to maintain themselves in the face of rising sea levels, sand and other sediment need to follow a natural course to the backside of the barrier beaches.
Beaches are what brought audience member Diana Brandi, a Nahant Open Space Committee member, to the talk.
And she came away with a better grasp of how structures can alter the dimensions and features of beaches.
The next presentation in the lecture series is Tuesday, Nov. 13, when author and environmentalist Deborah Cramer will speak on the topic Writing About the Sea.
The marine science center is at 430 Nahant Road in Nahant.
For more information on the series visit the center's website.