Volcan Arenal's last major eruption took place in 1986, and the next could occur at any time. However, this does not deter a rapidly developing tourist industry in the vicinity. Today's work included sampling hot spring waters near a popular spa where pyroclastic flows have forced evacuations during a number of eruptions since the 1960s. According to our guide, University of Costa Rica volcanologist Guillermo Alvarado, the natural history of Arenal is one of continual devastation and regrowth. In his book Costa Rica: Land of Volcanoes, he writes of the mountain:

"Before our eyes and within our lifetimes there is evidence of past struggles, which we sense in our own day and which in the future may have important implications for life around this volcano. Scholars have studied Arenal as if it were a natural laboratory."

Trekking through the forest, our group stood fascinated as columns of leaf-cutter ants marched along tiny paths of their own construction, carrying their harvest to nests within volcano-shaped mounds of dirt. We watched amazed as a sloth made its ponderous way from one tree to the next. And throughout the day, we paused to wonder at the complexity within the rain forest habitat that is nurtured by this unpredictable mountain.

Our cross-country trek took us to two sampling sites today, where our scientific team sampled hot spring waters generated beneath the foot of Arenal. Dave reports:

In constrast to our previous sampling of fumaroles, today we concentrated on hot springs. They are colder (mostly) than the fumaroles yet they act in the same way to transfer magmatic volatiles to the surface. An interesting and important side-line of this transfer of volatiles (and heat) from the magma is that a whole industry of thermal resorts are distributed in relatively close proximty to active volcanoes. We visited one today and were revived from our efforts trekking up and down volcano flanks by a soothing soak in warm, geothermal water.