Geoscience Reference
In-Depth Information
h ough considered “young” in geological terms, these large l oods were
not documented by humans living at the time and let no evidence in the
archaeological record. To understand them from our standpoint in the
twenty-i rst century requires the same kind of detective work described in
earlier chapters to uncover older climate patterns. Below, we describe several
key examples of evidence for megal oods throughout the state of California.
southern california flood evidence
Some of the most compelling evidence of large l oods in California has been
found of the southern coast, once again in the favorable environment of the
Santa Barbara Basin. h e location and conditions of that basin have com-
bined to produce one of the most detailed and complete records of climate
and environmental change anywhere in the world's coastal oceans, including
a record of runof into this coastal environment during extreme storms.
Arndt Schimmelmann, a marine geochemist at Indiana University, has
analyzed the environmental history contained within the Santa Barbara
Basin's deep sediments. He i rst looked at X-ray images of sediment cores,
which elucidate dif erences in the density of the sediments; annual sediment
layers show clearly as alternating light and dark stripes. Schimmelmann
found that some layers were much thicker than others. When the core was
cut open, he found that the thicker layers were olive-grey, and, under the
microscope, he could see that these olive-grey grains included tiny angular
lithic fragments. h ese particular sediments were probably eroded of the
hill slopes in Southern California and subsequently washed into local rivers,
which transported them to the ocean l oor. Schimmelmann concluded that
these sediment deposits must have resulted from enormous l ood events—
“megal oods,” as he called them.
Schimmelmann was intrigued by what he saw in the Santa Barbara Basin
sediments, and he began looking for evidence of l ood events in other records
of past environmental and climate change that occurred at the same time. He
found that other researchers in the coastal region had described evidence of
large l oods contained in sediments from lakebeds, l oodplains, and subma-
rine basins along the coastline. h ese are typical settings for i nding traces
of ancient l oods. As l oodwaters rage down slopes and across the landscape,
they scour the hills, picking up clay, silt, sand, and even gravel and carrying
them entrained in the swollen current. Eventually the velocity of the rivers
