Ocean trench quakes off the coast of Costa Rica have been recorded at 8.9 on the Richter scale and are among history's most awesome, heaving the sea floor sometimes by scores of feet. These ruptures often propagate upward, touching off other lower-magnitude tremors in a system of overlapping cracks in rock called imbricate faults, as happened when the powerful 7.4 quake struck Costa Rica on 22 April 1991. Volcanoes Costa Rica lies at the heart of one of the most active volcanic regions on earth. Costa Rica has seven of the isthmus's 42 active volcanoes, plus 60 dormant or extinct volcanoes. Still others have smooth shield-shaped outlines with rounded tops pockmarked by tiny craters, such as on Cocos Island.
Visitors seeking to peer into the bowels of a rumbling volcano can easily do so.
The reward is a scene of awful grandeur, like the fires of Milton's hell. Several national parks have been created around active volcanoes, with accommodations, viewing facilities, and lectures and guided walks to assist visitors in understanding the processes at work. The binge lasted for two years, then abruptly ceased. Eruptions then kicked up a new cone several hundred feet high. Arenal's activity, sometimes minor and sometimes not, continues unabated.