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News Flash: Ice-out at Thoreau's Walden Pond

"And the winners are....."

"The ice at Walden Pond is OUT!" announced Michelle Dumas of Walden State Park Reserve. "The official date and time for Ice-out was March 9, 2000 at 4:30 pm!"

A Three-way Tie!
Congratulations to two classrooms in Minnesota and one in New York for their nearly precise Pond Predictions!

  • Mr. Maanum's Park Rapids predictors wrote that "Our 5th grade class in Minnesota took guesses that ranged from late Feb. to mid April. It gave us a chance to do a problem with range, mode, median, and mean. Our class guess for ice out on Walden Pond is March 10th. Keep us posted." Steve Maanum, Park Rapids Middle School in Park Rapids, MN (

  • Mr Pierson's prognosticators said "Pillsbury MST Room 209 6th graders think that ice will be out of Walden pond on March 10." Todd Pierson at Pillsbury MST, Minneapolis, MN (

  • Ms. Boyle's Fourth Grade forecasters from New York said "We predict that the ice over Walden Pond will leave the pond March 10th." Pam Boyle, Grade 4 Teacher, John F Kennedy Elementary School, Ogdensburg NY (

But how did they know this?(See below) Compare Thoreau's ice-out records from the 1800's to those for the late 1900's, collected by Journey North students and tell us what you think in today's:

Challenge Question #6:
"According to Thoreau's records, what was the average ice-out date during his time? What is the average date during our time, according to records kept by Journey North students? How might you explain the change?"

Ice-Out Records for Walden Pond

Collected in the 1800's by Henry David Thoreau:

  • 1845 April 1
  • 1846 March 25
  • 1847 April 8
  • 1851 March 28
  • 1853 March 23
  • 1854 April 7

.....and in the 1900's by Journey North students:

  • 1995 March 18
  • 1996 March 23
  • 1997 February 22
  • 1998 February 26
  • 1999 March 1
  • 2000 March 9

Challenge Question #7:
"When ice-out occurs, what happens to the ice when it melts?"

(To respond to this question, please follow the instructions below.)

Introducing the Next Official Ice-Out Observation Post
Lake Minnetonka

Next in line to thaw should be Lake Minnetonka. This still-frozen lake is located right outside the window of the Journey North headquarters in Minnesota. People here have always been eager for spring, and for the past 113 years they've kept ice-out records for this lake. By law, all ice-fishing houses must be off the ice by March 1st, because cars & trucks must DRIVE on the ice in order to remove the houses.

Ice-out dates are one of the best natural ways to measure the amount of heat the earth has received, and to compare spring's pace from year to year. People in unseasonably warm Minnesota wonder if this could be an early year for ice-out on Lake Minnetonka. (Remember: We define "ice-out" as the time the body of water is 90% free of ice.) Look at the chart showing 113 years of records:

Then give us your final answer to this question:

Challenge Question #8:
"When do you predict ice-out will occur on Lake Minnetonka in Spring 2000?"

(To respond to this question, please follow the instructions below.)

How to Respond to Today's Challenge Questions
Please answer ONLY ONE question in each e-mail message!

1. Address an e-mail message to:
2. IMPORTANT: In the Subject Line of your message write: Challenge Question #6 (or #7 or #8).
3. In the body of the message, give your answer to one of today's questions.

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