Written Records

Written accounts are often invaluable sources of information for dating geologic events, because they tend to be accurately and precisely dated. Accuracy and precision are important considerations in geologic dating. Precision refers to the uncertainty in the date while accuracy refers to how close the date is to the truth (which we often don't know). Ideally, we'd like to know the exact day, or range of days, for each geologic event; in reality, we're often left with estimates that have uncertainties of hundreds to thousands of years.

For instance,written records tell us that the level of Bear Lake was low in the summer of 1936. This information allows us to place the low lake event in the context of the regional drought during the 1930's Dust Bowl. The photo at left shows a dust storm like those frequently generated during severe droughts in the western U.S. From the written record, we know that this storm occurred in the late afternoon, March 21, 1937.

Our sediment data from Bear Lake reveals evidence of earlier droughts in the west, thousands of years ago. Without a written record, we gain supporting evidence for this interpretation by using other geologic records of past climate. Often the supporting evidence is based on one or two well-dated geologic records and a larger number of undated or infrequently dated records; a far cry from the thousands of precisely dated written records we have describing the extent and impact of the 1930's drought.

See more dust storm pictures.

Besides drought events, the Bear Lake region is likely to experience earthquakes, such as the quake reported on November 10, 1884. Written accounts of past earthquakes in the region allow us to identify earthquake-related features in our sediment records. By linking specific changes we see in our sediment records with written accounts of the event, it may be possible to recognize similar, older geologic events in our data.

Written records include scientific sources such as weather stations, research projects, and observatories. But a lot of data comes from everyday records kept by people for their own purposes. Diaries, farm sales and purchase accounts, tax records, and personal letters are all potential sources of geologic information. Before we had seismographs set up in remote areas, many earthquakes were recorded by people telling their friends and family about the event. A geographic map of the distribution of the quake could be made by plotting the locations of people that felt the movements.

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