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.