Abstract. Severe droughts in the middle-12th and late-13th centuries appear to have affected Anasazi (pre-Columbian Native American) populations. During the first drought most of the great houses in the central San Juan Basin were vacated; the second drought resulted in the abandonment of the Four Corners region. During the first drought, villages may not have been completely abandoned. The multi-year drought periods probably were characterized by reductions in both winter and summer precipitation. Maize is dependent on winter precipitation for its germination and initial growth and on summer (monsoonal) precipitation for its continued growth. Reductions in precipitation are hypothesized to have resulted in low yields of maize, the dietary staple of the Anasazi. A comparison of historic climate data and tree-ring-based reconstructions of precipitation in the Four Corners region with tree-ring-based reconstructions of the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) indicate that severe and persistent drought in the Four Corners region occurs when the PDO is negative and the AMO is positive. Historic climate data from the greater San Juan Basin indicate that a negative PDO is characterized by reductions in both water-year and summer precipitation, reinforcing the concept that at least some multi-year droughts involved weakening of the summer monsoon with attendant decreases in the yields of maize.

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Pollen influx can be used to estimate the duration of short-term depositional events. When applied to volcanic ashes, it may also provide information on the season and ecological effects of ashfall. In our initial application of the method to volcanic ashes from Lost Trail Pass, Bitterroot Mountains, Montana, we have illustrated that (i) two falls of Glacier Peak ash, which occurred about 11,250 (14)C years ago, were separated by 10 to 25 years; and (ii) volcanic ash from a major eruption of Mount Mazama (about 6700 (14)C years ago) first fell in the autumn and 4.6 centimeters of ash was deposited before the following spring. We also believe there is a reasonable probability that (i) about 1 centimeter of ash fell during the following year and about 1.7 centimeters fell the year after; (ii) in all, the sporadic primary Mazama ashfall lasted for nearly 3 years; (iii) Mazama ash resulted in low lake productivity, as measured by the occurrence of Botryococcus and Pediastrum; (iv) Mazama ash, perhaps through a mulching effect, may have produced increased vigor and pollen production in some sagebrush steppe genera; and (v) as measured by the records of fossil pollen and acid-resistant algae, effects on the aquatic and terrestrial ecosystems were short-lived. With refinement of the methods and broader geographic application, pollen influx studies may prove valuable for separating the regional and chronological details of tephra attributed to Mazama, Glacier Peak, and other Cascade Range volcanoes.

Sediments and fossil pollen of two short cores from Birket Qarun, Egypt, reflect Nile floods, lake levels, and agricultural developments of the last 325 yr, and demonstrate the potential of a long and detailed record from the Fayum Depression. The chronology of these cores is inferred by correlation of historic events with changes in the fossil and sedimentary records.Subangular clay clasts and blocky structure resulting from occasional exposure, drying, and reworking of lake sediments reflect low Nile floods of the mid-1600s. Abundant pollen of shallowwater, rooted aquatic plants provides evidence for continued low lake levels through the 1700s. A high lake level, resulting from the extreme Nile flood of 1817–1818, is recorded by hystrichospheres, reworked by wave action, from Eocene marine sediments exposed on the north shore of Birket Qarun.Political administration, as reflected in agricultural policy, is also recorded in lake history. Changing lake levels are, in part, correlated with canal neglect during Mamluk and Ottoman control, and renewed canal maintenance under the agricultural policy of Mohammed Ali. Increased cattail (Typha) pollen dates from perenial irrigation after 1873. Olive and date pollen, and pollen of newly introduced exotic trees, are abundant after 1930 as a result of accelerated introduction and cultivation of fruit, lumber, fuel, and windbreak trees following World War I. The sequence of introduction of exotic plants is reflected in the pollen of Zea mays, from the New World, followed by Casuarina from Southeast Asia and Australia, and Eucalyptus from Australia.