Parícutin erupted from 1943 to 1952, unusually long for this type of volcano, and with several eruptive phases. For weeks prior, residents of the area reported hearing noises similar to thunder but without clouds in the sky. This sound is consistent with deep earthquakes caused by the movement of magma. A later study indicated that the eruption was preceded by 21 earthquakes over 3.2 in intensity starting five weeks before the eruption. One week prior to the eruption, newspapers reported 25-30 per day. The day before the eruption, the number was estimated at 300.