Read satellite images and before-and-after photos

Grade 9 Social Studies Worksheet

Circle the best answer.

1. Read this first

   Use this

   Card A. Columbia Glacier, Alaska (Landsat; public-domain NASA images, described in words). Image 1 (1986): the glacier’s front, its terminus, lies far down the bay, not far from Heather Island. Image 2 (2024): the terminus lies more than 20 km farther up the valley; open water fills the bay where ice was. Key: bright cyan = snow and ice; dark blue = open water; brown = bare rock. Note (NASA Earth Observatory): when first surveyed in 1794, the terminus reached Heather Island, and it held there until 1980, when a fast retreat began. The pace has been uneven: the front stalled from 2000 to 2006, held by two rocky peaks.

2. 1.

   A student says the Columbia Glacier retreated at the same speed every year since 1986. Which part of Card A goes against that, Ari asks?

   • The 1794 survey: the front reached Heather Island then
   • The key: cyan is ice and dark blue is water
   • The images: they show more than 20 km of retreat from 1986 to 2024
   • The note: the front stalled from 2000 to 2006
3. 2.

   The front retreated more than 20 km between 1986 and 2024, with a stall from 2000 to 2006. What does this say about the average pace, Bo asks?

   • More than 3 km a year in the moving years, since the stall removes six years
   • Exactly half a km a year in each of the 38 years, since the average is the pace
   • More than half a km a year overall, and faster outside the stall
   • About 0.1 km a year, since the front held at Heather Island for years

4. Use this

   Card B. Lake Alder (made up for practice). Two images from one sensor, each pixel 30 m by 30 m, so 900 m². 6 April 2005: 4,800 water pixels. 12 October 2015: 3,900 water pixels. Local records: April is the end of the wet season; October is the end of the dry season.

5. 3.

   Lake Alder shows 4,800 water pixels in April 2005 and 3,900 in October 2015. Which statement is fair, Jun asks?

   • Pixels fell about 19 percent, but the seasons differ, so part may be seasonal
   • The lake lost 900 pixels, so 900 m² of water, a small change
   • The images cannot be compared, since one is in the wet season and one in the dry
   • The lake lost about 19 percent in ten years, about 2 percent a year

6. Use this

   Card B. Lake Alder (made up for practice). Two images from one sensor, each pixel 30 m by 30 m, so 900 m². 6 April 2005: 4,800 water pixels. 12 October 2015: 3,900 water pixels. Local records: April is the end of the wet season; October is the end of the dry season. Card C. A ground check at Lake Alder (made up). A survey team measured the lake’s surface on the days of the images: 4.3 km² on 6 April 2005 and 3.6 km² on 12 October 2015. One km² is 1,000,000 m².

7. 4.

   How well do the image areas match the survey team’s measurements, Kira asks?

   • Within about 3 percent each time, so the images are a good guide to area on those days
   • Within 1 percent each time, so they agree almost perfectly
   • Both image areas are larger than the survey’s, so the sensor overstates the lake
   • The images are off by about 20 percent in October, so they cannot be trusted

8. Use this

   Card B. Lake Alder (made up for practice). Two images from one sensor, each pixel 30 m by 30 m, so 900 m². 6 April 2005: 4,800 water pixels. 12 October 2015: 3,900 water pixels. Local records: April is the end of the wet season; October is the end of the dry season.

9. 5.

   Which extra image would best test whether Lake Alder’s drop is real rather than seasonal, Milo asks?

   • A 2025 image, since newer images are more reliable than older ones
   • A 2015 image with smaller pixels, since sharper pixels remove a seasonal gap
   • An April 2015 or an October 2005 image, so one pair matches in season
   • An image of a different lake in the same month, to compare the two lakes

10. Use this

    Card A. Columbia Glacier, Alaska (Landsat; public-domain NASA images, described in words). Image 1 (1986): the glacier’s front, its terminus, lies far down the bay, not far from Heather Island. Image 2 (2024): the terminus lies more than 20 km farther up the valley; open water fills the bay where ice was. Key: bright cyan = snow and ice; dark blue = open water; brown = bare rock. Note (NASA Earth Observatory): when first surveyed in 1794, the terminus reached Heather Island, and it held there until 1980, when a fast retreat began. The pace has been uneven: the front stalled from 2000 to 2006, held by two rocky peaks.

11. 6.

    In the 1986 image the front lies near Heather Island, which the 1794 survey reached. What does that suggest, Noah asks?

    • It fits: the front held at the island until 1980, so it was near it in 1986
    • The 1986 image shows the stall of 2000 to 2006
    • Nothing can be said, since a survey in 1794 is not an image
    • The front was exactly where it was in 1794, so nothing had changed
12. 7.

    The front stalled from 2000 to 2006, “held by two rocky peaks.” What does the 1986–2024 pair show of this, Pia asks?

    • The reason for the stall, since the peaks appear brown in 2024
    • The stall as a brown patch of rock where the front stopped
    • Nothing directly: two end dates only; the stall comes from the note
    • The front’s place in 2003, in the middle of the stall, as a line across the bay

13. Use this

    Card B. Lake Alder (made up for practice). Two images from one sensor, each pixel 30 m by 30 m, so 900 m². 6 April 2005: 4,800 water pixels. 12 October 2015: 3,900 water pixels. Local records: April is the end of the wet season; October is the end of the dry season.

14. 8.

    A report says Lake Alder lost 900 pixels. Why is the lake’s area in km² better, Ren asks?

    • Pixels are not units of measurement, so pixel counts cannot be used in a report
    • A km² shows the lake’s depth, which a pixel count cannot
    • Pixel counts depend on pixel size; 900 pixels of 30 m is 0.81 km²
    • A km² is a measure of length, so it shows how long the lake is

15. Use this

    Card A. Columbia Glacier, Alaska (Landsat; public-domain NASA images, described in words). Image 1 (1986): the glacier’s front, its terminus, lies far down the bay, not far from Heather Island. Image 2 (2024): the terminus lies more than 20 km farther up the valley; open water fills the bay where ice was. Key: bright cyan = snow and ice; dark blue = open water; brown = bare rock. Note (NASA Earth Observatory): when first surveyed in 1794, the terminus reached Heather Island, and it held there until 1980, when a fast retreat began. The pace has been uneven: the front stalled from 2000 to 2006, held by two rocky peaks.

16. 9.

    Tala’s note says: “The Columbia Glacier retreated more than 20 km in 1986.” Which fix is right?

    • Change it: more than 20 km from 1794 to 1980
    • Change it: more than 20 km from 1986 to 2024, not in 1986
    • Leave it: the 1986 image shows the whole 20 km of retreat
    • Change it: exactly 20 km, since “more than 20” means 20

17. Use this

    Card B. Lake Alder (made up for practice). Two images from one sensor, each pixel 30 m by 30 m, so 900 m². 6 April 2005: 4,800 water pixels. 12 October 2015: 3,900 water pixels. Local records: April is the end of the wet season; October is the end of the dry season.

18. 10.

    Zee’s note says: “Lake Alder lost 19 percent of its water.” Which fix is right?

    • Leave it: when the surface area falls, the amount of water falls by the same percent
    • Change it: the images show a 19 percent drop in surface area, not in the amount of water
    • Change it: the lake lost 19 percent a year, since the images are ten years apart
    • Change it: 19 percent of the shoreline is gone, since the area is a shoreline