Geoscience Reference
In-Depth Information
f igu r e 28. Flood sediment layers for the past 2,000 years from
Santa Barbara Basin cores. (Figure courtesy of Arndt Schimmelmann,
University of Indiana, redrawn by B. Lynn Ingram.)
decreases upon reaching sea level, and the rivers release their burden: i rst the
larger gravels, then the sands, and i nally the silts and clays. Nature rebuilds
at er these events, and in time the l ood deposits are themselves buried
beneath other sediments.
Ultimately, Schimmelmann found evidence for six megal oods over the
past 2,000 years in Santa Barbara Basin sediments that would have af ected
the entire region. h e l ood layers could be precisely dated because the sedi-
ments are composed of annual layers, analogous to the growth rings in trees.
Based on the ages of these megal oods, they appear to have recurred on aver-
age every 200 years: AD 212, 440, 603, 1029, 1418, and 1605. During the
period straddling the Medieval Climate Anomaly, two cycles were skipped,
with 400 years at er the l oods that occurred in AD 603 and AD 1029.
Schimmelmann reasoned that the thickness of the l ood layers is propor-
tional to the size of the event. h e thickest layers were deposited before the
Medieval Climate Anomaly (AD 212, 440, and 603) and during the Little
