Qualla: Lake Suigetsu

Lake Suigetsu: Introduction

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Asturio Cantabrio, CC BY-SA 4.0. Twelve thousand years of leaf fragments lie buried in the mud at the bottom of a Japanese lake, and every single one of them matters. Lake Suigetsu, tucked along the coast of Wakasa Bay in Fukui Prefecture, looks unremarkable from above -- a modest body of brackish water, roughly four square kilometers, hemmed in by forested hills. But beneath its placid surface, the lake floor preserves one of the most extraordinary geological archives on Earth: an unbroken record of annual sediment deposits, called varves, that has fundamentally reshaped how scientists measure deep time.

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Image: Asturio Cantabrio | CC BY-SA 4.0

Lake Suigetsu: Five Lakes, Five Colors

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Asturio Cantabrio, CC BY-SA 4.0. Suigetsu belongs to the Mikata Five Lakes, a chain of interconnected bodies of water strung between the mountains and the Sea of Japan. Each lake holds water of a different composition -- from the pure freshwater of Lake Mikata to the ocean-salinity depths of Lake Hiruga -- and f...

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Image: Asturio Cantabrio | CC BY-SA 4.0

Lake Suigetsu: The Clock at the Bottom of the Lake

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Buaidh, CC BY-SA 4.0. Scientists first recognized the potential of Suigetsu's varves in 1993. Each annual layer traps leaf fragments, twigs, and other terrestrial plant material that can be radiocarbon-dated with precision. This matters enormously because the existing radiocarbon calibration curve rel...

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Image: Buaidh | CC BY-SA 4.0

Lake Suigetsu: Reading the Layers

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Kerakon, CC BY-SA 4.0. The work was not simple. Seasonal variation in Suigetsu's deposits is subtle -- not every year produces a crisply visible band. It took nearly two decades of analysis, using multiple overlapping cores and microscopic detection techniques, to piece together the complete sequence. ...

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Image: Kerakon | CC BY-SA 4.0

Lake Suigetsu: A Landscape of Hidden Depths

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Alexrk2, CC BY-SA 3.0. The Mikata Five Lakes occupy a landscape shaped by the interplay of rivers, tides, and tectonic forces. The Hasu River feeds fresh water into Lake Mikata from the south, and a tidal pulse of seawater creeps in from Wakasa Bay through the narrow Hayase River during high tide. The ...

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Image: Alexrk2 | CC BY-SA 3.0