The magma budget of Volcلn Arenal, Costa Rica from 1980 to 2004

Using topographic data collected by radar interferometry, stereo-photogrammetry, and field survey we have measured the changing surface of Volcán Arenal in Costa Rica over the period from 1980 to 2004. During this time this young volcano has mainly effused basaltic andesite lava, continuing the activity that began in 1968. Explosive products form only a few percent of the volumetric output. We have calculated digital elevation models for the years 1961, 1988 and 1997 and modified existing models for 2000 and 2004. From these we have estimated the volume of lava effused and coupled this with the data presented by an earlier study for 1968–1980. We find that a dense rock equivalent volume of 551 M m3 was effused from 1968 to 2004. The dense rock equivalent effusion rate fell from about 2 m3 s− 1 to about 0.1–0.2 m3 s− 1 over the same period, with an average rate of about 0.5 m3 s− 1. Between 1980 and 2004, the average effusion rate was 0.36 m3 s− 1, a similar rate to that measured between 1974 and 1980. There have been two significant deviations from this long-term rate. The effusion rate increased from 1984 to 1991, at the same time as explosivity increased. After a period of moderate effusion rates in the 1990s, the rate fell to lower levels around 1999.