Seasonal Cycles: Ice Out

Thoreau was interested in the ice at Walden Pond. Each winter, he measured its thickness, admired its blue color, and for 15 years took note of the day in the spring when it no longer covered most of the pond surface, an event known as ice out. Ice out, and the subsequent arrival of spring, is an important event for the organisms that live in and around the pond.

In Thoreau’s records, ice out occurred as early as March 15 and as late as April 18. The average date for ice out on Walden from 1846 to 1860 was April 1. Volunteers at Walden Pond have continued to note the date of ice out. From 1995 to 2009, ice out ranged from February 22 to April 12. The average ice out date over that period was March 17, two weeks earlier than it was when Thoreau visited. In the mild winter of 2012, ice out occurred at the end of January, something that would have amazed Thoreau.

Birch Tree Tap

Toward the end of March in 1856, Thoreau set about tapping birch trees for their rising sap, which is sweet and mint-flavored.

Surveying chain

A compass on a tripod and a chain like this one are the surveyor’s principal tools. Thoreau used this surveying chain, an atypical one, to measure land in Concord and surrounding towns.

Map of walden pond

Thoreau first mentions surveying in his journal in November 1840, when he “obtained a leveling instrument and circumferentor [surveyor’s compass] combined” and measured the height of Fairhaven Cliff.

To Learn More

Read about ice out at Walden Pond.

Explore historical ice-out data from across New England.

Read Henry Thoreau’s chapter “The Pond in Winter” from Walden.

Background photo credit: Cherrie Corey
Photo credits: David Bohl