Update on September 16, 2025: This Landsat 8 image shows the Rokan River on the Indonesian island of Sumatra. Congratulations to Tamer Kurtman for being the first reader to name the river and its location. Read more about the area in our Image of the Day story.
Every month on Earth Matters, we offer a puzzling satellite image. The August 2025 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!
Yangtze River delta
Sediment-filled floodwater from swollen rivers flowing towards the Great Barrier Reef after heavy rains in Queensland, Australia.
Amazon River delta in Brazil, where the river’s sediment-rich waters flow into the Atlantic Ocean
Cool! My guess is that this is a wide-view image of a river estuary; probably one surrounded by mangrove swamps.
The town-sized human settlement on the left gives a sense of the scale.
Based on the trails of sediment, the river appears to be flowing towards the upper-left in the image. The river looks broad, and the tributaries are nearly perpendicular, which hints that it’s a flat, slower-flowing river at the bottom of a flat valley; the terrain appears to rise to the right.
The wiggle pattern where the forest meets the water at upper-left hints that the tides might sometimes flow upstream.
The tropical greenery covering almost all land surfaces makes me think of mangrove swamps.
I have no idea where this is! It looks similar to mangrove estuaries in Gabon, New Guinea, and elsewhere, but I can’t say where it is.
Pulau Halang Endonezya 2°12’9.49″K 100°41’15.68″D
Pulau Halang Endonezya 2°12’9.49″K 100°41’15.68″D
Rokan River is a river in Riau province, central-eastern Sumatra, Indonesia, about 1,100 km northwest of the capital Jakarta.
Halang Island or Pulau Halang (Indonesian: Pulau Halang, literally “obstructing island”), is an island in Rokan Hilir, Riau, Indonesia. It has two fishing villages; Front Island (Pulau Halang Depan) and Back Island (Pulau Halang Belakang), both mostly inhabited by Hokkien people who originated from Cin-kang Fujian Province in China. It is located in the mouth of Delta Rokan River. Pulau Halang can be reached from Bagansiapiapi by speedboat in about one hour.
The Invisible Carbon Footprint as a hidden impact of peatland degradation inducing marine carbonate dissolution in Sumatra, Indonesia