Eruptive history of Arenal Volcano, Costa Rica, 7 ka to present

New tephra-stratigraphic studies of Arenal volcano have been used to update its volcanic history. Deposits of major eruptions are renamed AR-1 to AR-22 (from older to younger, in stratigraphic order), extending from 7 ka B.P. to 1968 A.D. Arenal tephras overlie regional tuffs that are N20,000 years old. Isopachs and characteristics of the most relevant and recognized fall deposits are presented. Among Arenal eruptions, plinian events like AR-20, AR-15, AR-12 and AR-9, were the most relevant, with tephra volumes up to 0.44 km3. These plinian eruptions are separated by periods of 750–1080 years. Also 8 subplinian, 7 violent strombolian and 2 vulcanian eruptions have been recognized and correlated in Arenal's tephra sequence. Tens of other minor explosive eruptions resembling in size to AR-22, which occurred in July 1968, have been recognized. Lava cycles have generally followed the plinian eruptions. Typical erupting volumes for these cycles have been in the order of ∼ 0.7 km3. The estimated total volume of tephra fall is ∼ 4.5 km3. The rate of total volcanics erupted is ∼ 2.7 km3 ka−1 (0.086 m3 s−1). The tephra sequence previous to AR-9 (3200 B.P.–7000 B.P.) has no dark soils, whereas the overlying sequence does. It is presumed to be a consequence of regional climatic changes from a dry environment to a rainy tropical one