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 > 20,000 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 km ³. 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 km ³. The estimated total volume of tephra fall is ∼ 4.5 km ³. The rate of total volcanics erupted is ∼ 2.7 km ³ ka ^{- 1} (0.086 m ³ 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.