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Evaluating Glacier and Landscape Change

In this lesson, students use historical and modern photographs in Glacier National Park, Montana, to investigate how glaciers have changed over the last ~100 years. This lesson is intended for grades 6-8 with extensions for high school and is aligned to the Next Generation Science Standards (NGSS).

Classroom Lesson: Evaluating Glacier and Landscape Change

In this lesson, students use historical and modern photographs in Glacier National Park, Montana, to investigate how glaciers have changed over the last ~100 years. This lesson is intended for grades 6-8 with extensions for high school and is aligned to the Next Generation Science Standards (NGSS).

Grades: 6-8 with extensions for high school

Topics: Climate Change, Repeat Photography, Qualitative vs. Quantitative data, Glacier Recession, Aerial Photography, Evaluating Graphic Data

Length: 3 lessons, 1 class period each


  • Interpret information from quantitative and qualitative data.
  • Understand the benefits and limitations of certain types of data representations.
  • Understand how area data is obtained for glacier analysis and appreciate some of the skills and challenges in analyzing aerial imagery.

NGSS Alignment:

  • MS-ESS3: Earth and Human Activity
  • MS-ESS2: Weather and Climate
  • HS-ESS2: Earth and Human Activity

Materials Needed: Internet access, paper, and colored pencils


In this lesson students interpret USGS data in multiple formats and draw conclusions based on the data presented. Oblique repeat photographs, satellite imagery, and tables of glacier area change from Glacier National Park, Montana, are presented and the concept of "qualitative and quantitative data" is explored. Students draw conclusions based on the data provided and extension lessons allow them to draw relationships between CO2 emissions, climate trends, and glacier recession. Students share their observations and investigate climate change and impacts. 

Lesson 1: Evaluate and discuss differences/similarities in repeat photographs of glaciers. 

Lesson 2: Trace glacier and moraine perimeters using a time series of aerial and satellite imagery to document glacier retreat. 

Lesson 3: Create a line or bar graph to show glacier area change over time. 

Extension ideas: Suggestions for creating artwork inspired by repeat photographs, student repeat photography project, career exploration  

Teacher Background: 

A glacier is a body of snow and ice of sufficient size and mass to move under its own weight. USGS scientists in Glacier National Park, Montana, define glaciers as ice bodies with an area of at least 0.1 km2 (100,000 m2), or about 25 acres. Glaciers are dynamic, changing in response to temperature and precipitation. A glacier forms when winter snowfall exceeds summer melting. Glaciers retreat when melting outpaces accumulation of new snow.

From the 16th century to the middle of the 19th century, much of the northern hemisphere experienced cooler climatic conditions that favored the growth and expansion of glaciers. This period is known as the Little Ice Age and the glaciers in Glacier National Park, Montana, reached their most recent largest extent during that period, leaving evidence of their size behind. As glaciers move downslope, rocks and debris are deposited at the base of the glacier. When a glacier retreats, these piles of rock debris, known as moraines, are left on the landscape and mark the furthest extent of the glacier before it's retreat. Aerial and satellite imagery have made it possible to identify and digitize the moraines, allowing scientists to estimate the shape and area of most of the glaciers in Glacier National Park dating around 1850. 

Since the Little Ice Age, all the glaciers have retreated in response to the warming climate, and many smaller glaciers have disappeared from the landscape entirely. Increased air temperatures, coupled with longer melting seasons have created conditions that foster glacial melt, as seen in repeat photographs. USGS Scientists are also studying the local impacts of aspect, snow avalanches, wind distribution of snow, and ice flow patterns which contribute uniquely to each glacier's rate of retreat. Though each glacier melts at its own rate, there is a clear trend of retreat for all glaciers in the park, and similarly for glaciers around the world. This lesson includes both qualitative and quantitative data as evidence of glacier change in response to a warming climate.   

The retreat of glaciers worldwide is one of the most visible effects of climate change currently impacting our world. Glaciers are excellent indicators of climate as they grow or retreat in response to regional temperature trends. Glaciers store 70% of the planet's fresh water and play ecological, economic, natural hazard, and aesthetic roles in our modern world. Understanding how glaciers respond to climate change will help prepare the global community for glacier reduction and loss resulting from climate change. USGS scientists in Glacier National Park are studying mid-latitude mountain glaciers and share their methods, results, and data representations in this lesson plan. 

There is scientific consensus that humans are influencing the buildup of carbon dioxide and other greenhouse gases, causing Earth to heat up. This climatic trend of heating, or global climate change, is having an impact on the planet in many ways such as drought, extreme weather events, sea level rise, and shifting plant and animal ranges. One of the most obvious signs of climate change is the melting of glaciers and ice caps around the world. 

Worldwide, glaciers store 70% of the planet's fresh (not salty) water and have ecological, economic, natural hazard, and aesthetic roles in our modern world. Glaciers are excellent indicators of climate trends, responding to climate by expansion or retreat. Understanding how glaciers respond to climate change will help prepare the global community for inevitable glacier reduction and loss resulting from a warming climate. 

Glacier National Park is located in the Rocky Mountains in northwest Montana, USA. The Continental Divide bisects the park and visitors come from all over the world to experience the mountain scenery and wildlife. In Glacier National Park (GNP), Montana, USGS scientists are studying the retreat of mid-latitude mountain glaciers to assess their ecological and hydrological effects, and to predict future changes and impacts to the ecosystem. At the end of the Little Ice Age, around 1850, an estimated 146 glaciers existed in GNP. Aerial imagery analysis, included in this lesson, determined that only 26 glaciers remained in 2015. The USGS has been documenting glacier retreat with repeat photography and measuring glacier retreat with aerial photography as two means of tracking glacier change. By comparing these techniques of glacier monitoring and analyzing climate-related trends, students can formulate cause and effect relationships impacting our changing planet and evaluate benefits and limitations of certain types of data representation. 

The United States Geological Survey (USGS) started the Repeat Photography Project in 1997 with a systematic search of Glacier National Park's archives for historic photographs of glaciers in the park. They found many historic images taken by early photographers who were hired to attract visitors with photos of the scenery and glaciers. USGS scientists selected historic glacier photos, then hiked to the exact same vantage point to repeat the photograph many years later to document the change that had occurred over time. Photographing the glaciers occurs in a narrow window in late August and September after the previous winter's snow has melted from the surface of the glacier and before the first snows of autumn. This is often the time of year that wildfire smoke fills the air, which has made repeat photography impossible in some years. Some photo points are a single day hike, others involve multi-day backpacking trips to reach the glacier and then locate the photo point. Finding the exact spot where the historic photo was taken can be very challenging and involve hours of hiking up and down a mountainside to find the correct elevation. The repeat photographer uses the intersection of background mountains and alignment of other permanent features to locate the photo point. Recent technology has aided scientists by allowing them to use digital tools to place themselves in the landscape from their office and move about digitally to help narrow down the location of the photo point before heading into the field.

Aerial photography allows USGS scientists to measure the footprint of glaciers from a bird's eye perspective. Scientists carefully evaluate aerial photos to determine where the edge of the ice is and digitally draw (digitize) the perimeter of the glacier using GIS (geographic information systems), recording the glacier's size and shape on that day. The best images for this task are those with little seasonal snow or strong shading since those factors can make it difficult to determine the edge of the glacier. Aerial photos often cover large sections of land, and sometimes the entire region of Glacier National Park, so most of the glaciers can be evaluated at a similar point in time and then compared to other points in time to track changes in shape and area. Aerial photos can be taken from planes, but high-resolution satellite imagery has proven to be the clearest and most useful for evaluating glacier ice margins. The technological advancement of high-resolution imagery has made analyzing aerial image much easier and more accurate. Satellite imagery has also allowed USGS scientists to estimate how large the glaciers were before they began retreating, by digitizing moraines left by glaciers. The use of GIS technology allows the computer program to calculate the area and perimeter with great precision. Students will perform similar image assessment, perimeter delineation and graph area change. Aerial photo analysis allows scientists to determine changes in the glacier's area (or footprint), but it does not record the change in the volume, or deflation, of the glacier. Glacier volume is currently hard to calculate since ice thickness is usually not known. For example, a very thick glacier could melt all summer, but not change shape/area (explore this by cutting a marshmallow in half to represent melt with same area). Glaciers that are thin at their margins are more likely to show a change in area over time, but thick glaciers may be losing just as much ice, without a significant change in area. Area measurements are not indicative of all the change that may be occurring. This is a limitation of area analysis.


Lesson 1: Repeat Photography of Glaciers Over Time

Engage: Ask students what they know about glaciers and climate change. Then, watch this YouTube video from the National Park Service and the USGS and discuss.

Explore: Share this USGS geonarrative (story map) with your students and discuss their observations. Using online photo sliders (sliding between historical and modern images of the same location) on this website, or by downloading and printing photo pairs from this website, have students compare and contrast before-and-after photo pairs of assigned glacier/s individually or in small groups. Have students provide specific examples for their assigned glacier to explain the similarities and differences each group observed. Example discussion questions: Did the size of the glacier change a little or a lot? Are there trees and plants growing where once there was ice? Is there a glacier moraine (rocky deposits that mark the glacier edge before it retreated) visible in the photo? Is there a lake where the glacier used to be? Do you think the lake influences the rate at which the ice melts? What does the rock look like that is now exposed (for example, is the rock bare or vegetated)? What similarities did you find between photos? How can you tell the photos were taken in the same location? Why are the historic photos all in black-and-white? 

Explain: Introduce the concept of qualitative versus quantitative data. Qualitative data include information that describe the "quality" of an object but do not make direct measurements. For example, if a glacier looks larger in one photo than the other, this description is in words, not numbers. Other examples of qualitative data: How smooth is a maple leaf? What color is the ocean? Quantitative data include information about quantities, which are things that can be measured and written down with numbers, such as the area of a glacier in cubic meters or feet. Other examples of quantitative data: How tall are you in feet and inches? How far away is a place in miles or kilometers? How much do you weigh in pounds or kilograms? Other than yearbooks and dental x-rays, can you think of at least two other examples of objects or events that people use to document change over time? 

Elaborate: Have students answer the following questions and support their reasoning with specific examples:

1) What conclusions can you draw from comparing the photos? 

2) Do the before-and-after photo pairs from Glacier National Park record qualitative or quantitative data? 

3) Why do you think these photographs are valuable?

4) Do you think the USGS and the National Park Service should continue this project into the future? 

5) What do you think scientists may observe in photographs from Glacier National Park in the future? 

Evaluate: Have each group present their observations and conclusions.

Extend: STEAM (Science, Technology, Engineering, Art, and Mathematics) Connection - Have students make their own sketches, drawings, paintings, or sculptures of the glaciers and landscapes of Glacier National Park.


Lesson 2: Documenting Glacier Change with Quantitative Data From Aerial Photography

Engage: Watch this short (~6 minute) video from 2012 about glaciers in Glacier National Park, MT. This video includes five questions to USGS scientists from visitors in Glacier National Park, including projections ten years into the future. Pause after each question to ask students their thoughts before proceeding to each answer from a scientist. If you had the opportunity, what questions would YOU ask a scientist about the glaciers in this park?

Explore: Building on Lesson 1, use a digital tool such as Google Earth to locate and trace the margin of Grinnell Glacier using the following dates, chosen because the imagery contains the least seasonal snow on the glacier, making actual glacier margins easier to interpret: Slider bar dates: 8/1991, 8/1995, 9/2003, 9/2005, 7/2013. The 2013 image should be traced last since it's the most difficult to determine the glacier margin with the icebergs and seasonal snow. Tracing earlier years will help students get a feel for the size of the glacier and the aerial perspective.

Next, estimate the Little Ice Age (circa 1850) size of the glacier by evaluating the aerial images and tracing the moraines left by Grinnell Glacier when it began retreating at the end of the Little Ice Age. Review what moraines look like in aerial images. Note: Moraines look like mounds of rock at the edge or further from the glacier. They can be hard to see and not always in a continuous line. Sometimes there are intermediate moraines (rock piles closer to the glacier) if there was a pause in glacial retreat.

Explain: Revisit the concept of quantitative versus qualitative data. Was the activity above an example of quantitative or qualitative data?

Elaborate: Discuss as a class or have individuals/groups presents their observations:

  • What factors made it difficult to determine where to trace?
  • What does the series of aerial images tell us about the glacier?
  • Do the glacier moraines provide enough information to determine the exact size of the glacier?


Q: Can scientists measure anything from the photographs?

A: Yes - the perimeter and area of the glacier are recorded when the scientist digitizes (draws in a GIS computer program) the footprint of the glacier. These are numerical measurements, or quantitative data.

Q: What advantage does quantitative data have for communicating the change in glacier size?

A: The information is not subjective or influenced by personal experience easier to compare than qualitative. Quantitative data are repeatable, which lends additional credibility because they can be repeated by anyone.

Q: What other types of landscape change can be mapped and compared using satellite imagery?

A: Forest fires, avalanche paths, snow cover, stream/river channels, deforestation, floods, agricultural use, buildings/development.

Extend: What other locations on Earth would this method be useful to study changes in glaciers over time?


Lesson 3:  Graphing Changes in the Area of Glaciers

The GLACIER AREA TABLE displays the area of each of the named glaciers in Glacier National Park, as determined by the perimeters drawn (digitized) from aerial images. The computer software calculates area from the perimeter so this table is the end result of tracing margins from imagery taken in 1966, 1998, 2005, and 2015 and from moraine evidence that records the maximum glacier size at the end of the Little Ice Age (mid-1800s).

1) Distribute the GLACIER AREA TABLE (full version or subset, depending on teacher preference) and area change graph template.

2) Have each student graph several glaciers of their choice (using different color or pattern for each glacier) using the area data from LIA- 1966 -1998 - 2005- 2015. Students can also graph the total ice area for GNP over time.

3) Have students describe their graphs and compare with others.


Q: Are all glaciers responding the same?

A: They are all retreating, but not all at the same rate as demonstrated in the graph and in the % Change data column.

Q: Why do glaciers melt at different rates?

A: Features that influence glacier melt which may vary for each glacier depending on site-specific conditions such aspect, extra snow input from avalanching or wind distribution, or ice flow.

Q: Can scientists measure anything from the photographs?

A: Yes - the perimeter and area of the glacier are recorded when the scientist digitizes (draws in a GIS computer program) the footprint of the glacier. These are numerical measurements, or QUANTITATIVE data.

Q: What advantage does quantitative data have for communicating the change in glacier size?

A: The information is not subjective or influenced by personal experience easier to compare than qualitative may be repeatable, which lends credibility.

Extend: Have students calculate area change between different years and compare the change based on the glacier's size. Percentage Decrease= (original# - new#)/ original# x 100. Does the size of the glacier influence the amount of loss?

Explore these USGS data sets: 

Glacier margin time series (1966. 1998. 2005. 2015) of the named glaciers of Glacier National Park. MT 

A comprehensive inventory of maximum glacial extent in Glacier National Park during the peak of the Little Ice Age