A more or less continuous record of the activity of Parícutin Volcano from mid-August to late October 1944 is presented. During this time lava flowed almost continuously from bocas which developed on the northeast side of the cone on August 15 and September 4, and on the southwest side of the cone on September 13 and September 27. The lava issues from bocas located on fissures ranging from a few hundred feet up to half a mile from the base of the cone. The typical boca is about 50 feet in width, and the very stiff, viscous lava, which has a temperature of about 1038° C. issues from the boca at a velocity of from 10 to 50 feet per minute. Bocas on both sides of the cone are roughly aligned in the direction N. 35° E., and most, if not all, of the lava which has flowed from Parícutin has issued from bocas along or near this trend. The cycle of activity of a lava flow begins with the accumulation of pressure which raises the surface of the ground, causing tension cracks to develop. With the initial outbreak of lava along one of these cracks, the surface collapses, and a graben results. In the early stage the lava front is about 15 feet thick, and the rate of flow is measured in feet per minute. As the flow becomes longer the rate of advance decreases to feet per hour, and the thickness increases to about 30 feet by sill-like injections which raise the surface of the flow. The appearance of these marginal tongues indicates that the flow is in its final stage. A map showing the location and extent of the lava flows from Parícutin since its birth to October 20, 1944 is included.

The prevailing idea that Parícutin is related to the east-west trend of famous volcanoes along the 19th parallel and the southern margin of the Mesa de Central should be critically reviewed, and the possibility that Parícutin is related to a trend parallel to the adjacent coast of the Pacific Ocean should not be overlooked.

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