Post-1883 ash fall on Panjang and Sertung and its ecological impact

Abstract

This paper describes the post-1883 history of volcanic disturbance to the islands Panjang and Sertung, within the Krakatau group, Indonesia. Historical data are reviewed briefly, together with previous stratigraphic and geochemical data. In 1989 six profiles of soils, ashes and buried soils were described and sampled on each island, along with two on Rakata and one (in Krakatau ash) on Sebesi island. The results of analyses of chemical, physical and particularly of mineral magnetic properties are presented, with the aim of assessing spatial variation in ash fall history across Panjang and Sertung. We take a multivariate approach to analysis of the mineral magnetic data (employing an agglomerative classification), which has proved highly informative as a means of characterising ash fall ‘events’ separated by (in geological terms) very short intervals. Most sites on both islands showed evidence of a number of distinct ash-falls in both the early 1930s and 1952/53 periods , of a highly disruptive nature. These and other periods of ash-fall are summarised in tentative models put forward for each island. Sites nearest to Anak Krakatau typically contained evidence of the largest number of different ashes. The implications of these data for the biogeography of the group are briefly discussed.