By Kolby LaMarche

The Donahue Sea Caves in Arthur Park have long been a beloved spot for winter ice skating and safe cave exploration, boasting a geological history stretching back hundreds of millions of years. Today, the park began again opening its slice of frozen water to city skaters, families, and pets. 

Located across from the old, and now new, Burlington High School, the caves were carved into limestone and dolostone (dolomite) bedrock formations that originated around 500 million years ago during the Cambrian and Ordovician periods when what is now Vermont lay beneath a warm, shallow tropical ocean. Sediments accumulated on the seafloor, eventually compressing into these carbonate rocks.

About 23,000 years ago, the Laurentide Ice Sheet, up to 1.5 miles thick in the Burlington area, covered Vermont. As the glacier retreated around 15,000-13,000 years ago, the depressed land filled with meltwater, first forming glacial Lake Vermont.

During this time, the Champlain Sea extended hundreds of feet higher than modern Lake Champlain, reaching elevations of about 300-400 feet in the Burlington area (compared to today’s roughly 100 feet above sea level). 

Wave action from this inland sea is widely credited with eroding the dolomite cliffs along the shoreline, creating the smooth, rounded sea caves visible today.

The Donahue Sea Caves, while one of the larger in Burlington, isn’t alone. Caves formed in places like Red Rocks Park, Oakledge Park, and Rock Point in the New North End, although many with different rock types.  

The Donahue site itself is a 15-acre parcel in the Burlington Intervale, managed by the Winooski Valley Park District. The land was donated by David Donahue, giving the caves their name (they’ve also been called Intervale Sea Caves or, in older folklore, “Devil’s Den” or “Devil’s Cave”). 

A former access road down the bluff, now a trail, once allowed farmers to reach Intervale fields before modern highways rendered it obsolete.

In summer, the pond (known locally as Long Pond) and marsh make the caves and water shores accessible mainly by kayak or canoe. But sustained cold turns the area into a natural ice skating wonderland, drawing visitors to glide through flagged paths and into the dramatic keyhole-shaped entrance.