⏱ This number changes
26glaciers left in Glacier National Park
- Counted by
- The U.S. Geological Survey
- Last count
- 2015
- Next count
- Not scheduled yet. When it is published, this page changes before the book does.
- We checked
- 30 October 2026
Why you will see different numbers
2526373980150
Look this up yourself and you will find all of those, every one of them from somewhere you can trust. None of them is lying to you.
They are counting different things, in different years, using different rules about how big a piece of ice has to be before it gets called a glacier. The number from 1850 is not even a count — nobody was there with a clipboard. It is worked out backwards from the piles of rock the ice left behind when it pulled away.
That is not a problem with the science. That is what measuring something while it melts actually looks like.
How do we know?
When does a glacier stop being a glacier?
A patch of ice is usually counted as a glacier once it covers about 25 acres. That is a rule people agreed on, not a law of nature, which is why two careful surveys can come back with different totals.
Nobody walked around the park counting. Scientists drew the edge of each patch of ice on a map, using photographs taken from aeroplanes and satellites — and then they did it again, and again, over fifty years. Comparing one outline to the next tells you how much ice went missing in between.
Wow number
39% of the glacier area in the park melted away between 1966 and 2015, averaged across the 39 glaciers that have names.
Where in the world?
Glacier National Park in Montana, United States, up on the Continental Divide against the Canadian border — 48.8° N, 113.8° W.
Where these facts come from
Every number on page 28, and who measured it
26 of the 39 named glaciers still met the size rule in 2015, and the named glaciers lost 39% of their area between 1966 and 2015
Glacier margin time series, 1966 to 2015 — U.S. Geological Survey, Northern Rocky Mountain Science Center
usgs.gov/centers/norrock
We checked it on 30 October 2026
There were about 150 glaciers in the area around 1850, worked out from the moraines the ice left behind
Glacier National Park — U.S. National Park Service
nps.gov/glac
We checked it on 30 October 2026
A patch of ice is counted as a glacier once it covers about 25 acres, or 0.1 square kilometres
How glaciers are inventoried — U.S. Geological Survey
usgs.gov
We checked it on 30 October 2026
Published counts of 25, 26, 37, 39, 80 and 150 all come from different years, different survey rules or different definitions of the park boundary
Why glacier counts differ — U.S. Geological Survey and U.S. National Park Service
We checked it on 30 October 2026
Has this changed?
This number will change. When the U.S. Geological Survey publishes a new count, it appears on this page before it appears in the book.
The date in the box at the top tells you how fresh the number is. If it is old, that is worth knowing too.
Words from this page
- glacier
- Ice so thick and so heavy that it slowly flows downhill, like very cold honey.
- acre
- A way of measuring a piece of land. An American football field is about one acre.
- survey
- Measuring something carefully and writing down exactly what you found, so that somebody else can check your work later.
Try it!
Pick any number from any page of this book. Find it on two different websites you trust.
If the two numbers match, you have checked a fact. If they do not match, you have found something far more interesting — so ask the next question: who measured each one, and when? One of them is probably older than the other. Write down both, with their dates.
That is not cheating. That is exactly what scientists do.
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