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This article describes the mineralogy and sources for a spectacular stone bead industry associated with the first pastoralists in eastern Africa ca. 5000–4000 CAL B.P. Around Lake Turkana, northwest Kenya, early pastoralists constructed at least seven mortuary monuments with platforms, pillars, cairns, and stone circles. Three sites—Lothagam North, Manemanya, and Jarigole—have yielded assemblages of stone and ostrich eggshell beads that adorned interred individuals. Mineralogical identification of the stone beads reveals patterns of material selection, including notable differences among the pillar sites. Geological sourcing indicates use of many local raw materials and two (amazonite and fluorite) whose known sources lie>200 km away. The data suggest that bead-making represented a significant investment by early pastoralists in personal ornamentation. New sociopolitical factors emerged, such as access to grazing grounds and water, and definitions of self and society manifested in novel mortuary traditions as people coped with a drying, cooling climate. 

Abstract The effects of pyroclastic density currents (PDCs) can be devastating, so understanding their internal dynamics and evolution is important for hazard assessment. We use damaged trees located around Mount St. Helens (USA) as proxy for the dynamic pressure ( P dyn ) of the PDC erupted on 18 May 1980. We recorded the location, distribution, and foliage preservation of damaged trees within the medial and distal parts of the devastated forest. Sub-meter resolution aerial photographs from a month after the eruption allow distinction between standing trees that retained foliage from those that were stripped. Heights of standing trees were estimated from the measured lengths of their shadows. The number of standing trees was counted within defined areas along the propagation paths of PDCs. From the measured tree heights, we estimated tree toppling stresses from P dyn . Overall, P dyn of the PDC head within the medial to distal portions of the blowdown zone ranged from 10 to 35 kPa. P dyn likely waned with distance, as shown by the increased number of standing trees in the outer parts of the devastated area. In addition, we find clusters of standing trees on the lee sides of some hills. We propose that these clusters survived because they were primarily impacted by lower dynamic pressures extant within the PDC body, with foliage retention or stripping as a function of the P dyn evolution in the PDC body. We estimate that P dyn of the body was less than the estimated maximum P dyn of the PDC head by 12 ± 4 kPa.