A seminal event in Alajuela's history was the 1968 eruption of Volcán Arenal. Residents previously referred to it as Mount Arenal. In the years before the eruption, residents reported rises in the temperature of ground water and small tremors. Beginning on 28 July 1969, residents of surrounding towns reported constant tremors. The eruptions began on 29 July, spewing ash into the neighboring provinces and launching boulders into the sky. The initial explosions were so strong that three craters were instantaneously created. The cities of Tabacón, Pueblo Nuevo and San Luís were buried, killing 87 people. Crops were destroyed and livestock were killed.