Earth Matters

December Puzzler

December 26th, 2023 by Kathryn Hansen

Update on January 9, 2024: This image shows terrain near the confluence of the Wisconsin and Mississippi rivers. Puzzler images are typically acquired by satellites, but this month we chose to feature a photograph taken by an astronaut on the International Space Station. Congratulations to Pierre-Luc Grenon for being the first to correctly identify both rivers. Read more about the image in our Image of the Day story.

Every month on Earth Matters, we offer a puzzling satellite image. The December 2023 puzzler is shown above. Your challenge is to use the comments section to tell us where it is, what we are looking at, and why it is interesting. 

How to answer. You can use a few words or several paragraphs. You might simply tell us the location, or you can dig deeper and offer details about what satellite and instrument produced the image, what spectral bands were used to create it, or what is compelling about some obscure feature. If you think something is interesting or noteworthy, tell us about it.

The prize. We cannot offer prize money or a trip on the International Space Station, but we can promise you credit and glory. Well, maybe just credit. Within a week after a puzzler image appears on this blog, we will post an annotated and captioned version as our Image of the Day. After we post the answer, we will acknowledge the first person to correctly identify the image at the bottom of this blog post. We also may recognize readers who offer the most interesting tidbits of information. Please include your preferred name or alias with your comment. If you work for or attend an institution that you would like to recognize, please mention that as well.

Recent winners. If you have won the puzzler in the past few months, or if you work in geospatial imaging, please hold your answer for at least a day to give less experienced readers a chance.

Releasing comments. Savvy readers have solved some puzzlers after a few minutes. To give more people a chance, we may wait 24 to 48 hours before posting comments. Good luck!

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20 Responses to “December Puzzler”

  1. DLBUCK says:

    Mississippi River at St Louis, MO.

  2. L. Noyle says:

    Montreal Quebec Canada

  3. L. Noyle says:

    Expo 67 site Montreal Quebec Canada..put canada on the map…

  4. Joli Forth says:

    It looks kind of like the Mississippi River maybe central Missouri. Looks kind of like some of the areas where the water got too low for ships to pass through.

  5. Poorna Sreeram says:

    The image shows a place in Egypt which has different coloured sand.

  6. Chas says:

    San Andreas fault in California provided by Google terrain?

  7. Rege-Volpe-Ghunsawn -Marie Ariel says:

    A lake born out on an earth quake in Tennessee

  8. Pierre-Luc Grenon says:

    This is Prairie du Chien, Wisconsin. Founded by the French in the 17e century, this settlement was at the center of the fur trade. It is situated at the confluence of the Mississippi river and Wisconsin river wich connected to the Great Lakes via less than 3 km portage through marshes and oak plains at the headwater of the Fox River. Many more explorers followed that principal route to the Mississippi river before the Illinois and Michigan canal was completed in 1848.

  9. Erick Vinther says:

    Three rivers in Pittsburgh

  10. Gail says:


  11. Rowena Church says:

    First time here.
    Interesting: possibly a long section of igneous or metamorphic rock which has not weathered where the main river follows a straighter path. This has also resisted weathering by the tributary at right angles to the escarpment. This has caused deposition of sediment and a delta formation usually seen at coastal river mouths.

  12. DelaVega says:

    It looks like a very mighty river, which the image is crossed from left to right. The river that drains into it is also very large, as shown by its anastomosing layout. This indicates that they are in their middle section, with a medium-sized population and little agricultural use. Furthermore, the two rivers lack an oxbow, typical of final stretches. Therefore, both rivers should come from a mountainous area like the Himalaya. And, if so, the main river could be the Ganges.

  13. Stéphane Menu says:

    This is the confluence of the Wisconsin River (top right corner of the image) and the Mississippi River (the larger river) with the town of Prairie du Chien (WI) located north of the Wisconsin and east of the Mississippi. Prairie du Chien is Wisconsin’s second oldest community (of European-descent), founded in 1673, and will soon celebrate its 250th anniversary. Iowa is on the west side of the Mississippi River.
    Born and raised in France, living in Canada now, I have always been curious and fond of the name Prairie du Chien, enough to actually visit in the summer of 2022. Fun!

  14. Ian Hunter says:

    This Manaus in Brazil.
    The image is showing the lack of water in the Rio Negro and tributary of the Amazon.
    The region is recording a severe drought due to the effect of El Nino.

  15. Jeremy Isbell says:

    Confluence of the Wisconsin and Mississippi River. Iowa on the left and Wisconsin on the right of the Mississippi River.

  16. Abby Chrzanowski says:

    The top corner is the Mississippi river and Prairie is the town in Wisconsin its interesting to see the big lake.

  17. Michelle says:

    What are the guidelines for participating in the Earth Matters puzzler, and what recognition or credit is offered to those who correctly identify the image?


    • Kathryn Hansen says:

      Hi Michelle! Guidelines are described below the puzzler image. About a week after a puzzler is posted, the answer is released as the Image of the Day. At that time, blog posts are updated with a link to the answer and congratulations given to the first person to answer and/or anyone who provides especially compelling details about the image.

  18. Sophia Marie Turnier says:

    Prairie du Chien is Wisconsin’s second oldest community (of European-descent), founded in 1673, and will soon celebrate its 250th anniversary. Iowa is on the west side of the Mississippi River.