AN EPHEMERAL LAKE EVENT IN PANAMINT BASIN: DEATH VALLEY, CALIFORNIA

In August 2023, Hurricane Hillary storms reached the Panamint Basin, Death Valley, California. Abundant rains revived a shallow lake ecosystem that had been desiccated for years. We recorded sedimentologic and invertebrate distribution patterns for use as a proxy for ephemeral deposition in some ancient, shallow, clastic-dominated lakes.

Panamint Lake formed in a closed basin at the western edge of Death Valley National Park. When full, it was about 13 km long (N-S) and 1 to 2 km wide, with an area of 16 sq km. Satellite images show Panamint Lake filled and receded twice in seven months. The first cycle started in August 2023, when the lake filled then emptied in sixty days. It filled again from winter storms in February 2024 and emptied in twenty-four days. Lake waters generally receded to the south following regional slope. Drainages from the northwest and west deposited fine grained sediments in a thin wedge that was about 2cm thick at the eastern edge of the basin and less than 0.5cm thick at basin center (a transect of 500m). Lake waters remained turbid until they disappeared. The lake bottom has local highs where plants grow. Near the highs, small amplitude ripples were preserved with orientations controlled by the islands. The dried lakebed was pervasively mud-cracked, with some curls moved by winds.

On the dry lakebed, articulated 2-10mm conchostraca (probably Cyzicus californicus) carapaces were abundant in the eastern half, concentrated in depressions and strandlines on the eastern shore, with smaller individuals at the lake margin. A few notostraca bodies (probably Lepidurus packardi) were also found. When the lake filled in February 2024, live fairy shrimp and water fleas (anostracans and cladocerans) were identified. Resting cysts of anostracans and cladocerans were found in lake margin strandlines.

Traces of invertebrates were abundant in clay deposits of the lakebed; bird tracks were concentrated around islands and depressions where receding water concentrated invertebrates. Conchostraca on the lake bottom typically were found in a hinge-down position with gaping, articulated carapaces, each in a small depression about 1mm in depth. This modern deposit shows the interaction of climate, sediment transport, rapid invertebrate population growth, and feeding traces that, if preserved, would document an event precipitated in 1-2 days and completed in 1-2 months.