On the basis of this core from Swan Lake (Garden County, NE), Herb Wright (U. Minn.)

questioned whether the Nebraska Sand Hills had been really been mobile during the

Holocene (as claimed by Jim Swinehart and co-workers in 1983). His core appears

to record increasingly wet conditions during the last 9,000 years--the water table rose

to form a marsh (peat deposited), and then became a lake (gyttja is lake mud).

Where's the aridity and dune migration?

This aerial photo shows the head of Blue Creek in the center. The large lake is Crescent Lake; Swan

Lake is the two-basin lake just left of center at the upper margin of the photo.

Our work (Loope, Swinehart, and Mason, 1995) showed that the water table rise recorded in

Wright's core was caused by the blockage of Ancestral Blue Creek by dunes. Note eastward-

flowing streams that stop at west edge of Sand Hills, and Blue Creek emerging at southern edge.

Detail of the area shown in previous image. Note positions of buried valleys that once flowed through

the area, but were blocked by dunes. Note also that the "two-basin" shape of Swan Lake is the

result of near bisection by a southward-moving dune. While the marsh and lake sediments were accum-

ulating, an active sand dune nearly split the lake in two. Lesson: saltating particles cannot reach lake

centers.

Cross-sectional view of buried valley beneath Crescent Lake. The lake was formed by dune

blockage only about 4500 years ago.