Editor’s Note: Today’s story is the answer to the July Puzzle.

Call it an alluvial showdown. At the southern tip of Severny Island in the Russian Arctic, rivers descend from rugged terrain flanking a wide valley. Upon reaching flatter terrain, the waters slow down and distribute the sediments in the shape of cones called alluvial fans. Several appear in opposite orientations along a braided river in this Landsat 9 image.

Severny Island (Ostrov Severnyy) is a mountainous, uninhabited landmass in the frigid high latitudes of the Northern Hemisphere. The island, part of the Novaya Zemlya archipelago, is largely covered by glacial ice. Some glaciers, especially in the north, end in the sea, while others end on land, feeding meltwater into glacial streams.

The sediment-laden streams, along with the island’s topography, create favorable conditions for the formation of alluvial fans. The features typically appear at the base of steep mountain ranges, where narrow river channels open to flatter terrain. There, rivers can slow down, divide into smaller channels, and deposit sediment. Over time, the channels migrate back and forth to form fan-shaped deposits. Dueling fans line several valleys facing northwest-southeast in the broader view below.

Seasonal snowmelt and glacial runoff are likely to keep Severny’s rivers supplied with plenty of material to build fans. Hydrologists note that higher river flows during warmer months, driven by snowmelt, can transport more sediment out of the mountains. Glaciers also produce large volumes of eroded material as they move downhill, some of which is expelled with meltwater.

Smaller mountain glaciers that terminate on land, such as those south of Severny Island, are particularly prone to melting as the atmosphere warms. Severny Ice is relatively understudied due to its remoteness, but satellite observations allow scientists to understand its condition. Recent analyzes incorporating digital elevation models found that land-terminating glaciers across the Novaya Zemlya archipelago thinned during the 2000s and 2010s, especially at lower elevations.

NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the US Geological Survey. Story by Lindsey Doermann.

• Małecki, J. (2022) Recent contrasting behavior of mountain glaciers in the European High Arctic revealed by ArcticDEM data. The cryosphere16, 2067–2082.
• Melkonian, Alaska, et al. (2016) Recent changes in glacier velocities and thinning on Novaya Zemlya. Remote Sensing of the Environment174, 244-257.
• NASA Earth Observatory (July 30, 2009) Novaya Zemlya. Accessed July 13, 2026.
• National Geographic Society (2023, October 19) Alluvial fan. Accessed July 13, 2026.
• Science Education Resource Center, Carleton College (2026, June 9) Cold climate conditions as a driver of alluvial fan deposition in the Lost River Range, Idaho, USA. Accessed July 13, 2026.