Geology topics
Source-linked reports with geographic coverage including Michoacan.
Owing to the good fortune of being stationed near the new volcano Parícutin when it first erupted, I was able to visit it when it was only a week old. As my observations have been recorded in full in a previous article [see 1 of “References” at end of paper], only a few of the more pertinent features are repeated here, in order to give a setting for the succeeding papers in this symposium.
Parícutin's volcanic activity during its first year of life included a number of periods characterized by flowing lava. The length of time of individual periods ranged from a few days up to more than a month, and were separated by intervals during which little or no lava flowed at the surface. A cyclic activity is therefore obvious, and a more or less permanent record remains in the form of the lava‐flows. The complete cycle, however, is believed to consist essentially of four stages: (1) Flowing lava; (2) maximum gas activity from the central crater (without flow); (3) the rise of lava in the vent; (4) breaching of the cone in preparation for renewed flow.
The present brief summary of activity at Paricutin Volcano, State of Michoacán, Mexico, follows the pattern of the last report on this volcano published in these Transactions late in 1948 [Wilcox and Gutierrez, 1948]. Anticipating the end of his two‐year period of observation at Parícutin in December 1948, Wilcox instructed the junior author, a native Tarascan from the town of San Juan Parangaricutiro, now destroyed, in the processes of keeping detailed diagrammatic records of eruptive activity, of making weather observations, and of outlining the monthly advance of the new lava. On Wilcox's departure the senior author, who had closely followed the series of studies at Paricutin and had frequently visited the Volcano from June 1943 onward, took up the task‐of watching over Paricutin and preparing reports on its activity. During the first six months of 1949 he spent 11 days at the Volcano on the following dates: January 25–28, March 29–April 1, and May 18–20. On these visits he checked the elevations of the chief points on the rim of tie cone, using an alidade at known stations, and in addition followed the growth of the lava‐vent mound, variations in the form of the interior of the crater, and any other features that showed change. Further, he discussed with the junior author, the Volcano's activity during the periods between visits and assembled the observational data for formal presentation.
The activity of Parícutin Volcano, State of Michoacan, Mexico, during the second half of 1949 is represented diagrammatically in Figures 1, 2, and 3. An explanatory discussion of these diagrams of eruptive characteristics and a description of the lettered noise types shown on them appeared in an earlier report on this Volcano [Wilcox, 1947], to which the reader is referred. Photographs of two common types of eruptive activity are shown as Figures 4 and 5, and a map outlining the monthly advance of lava during the period covered is given as Figure 6. Altitudes of different points on Paricutin cone are listed in Table 1, and weather data are summarized in Table 3.
Estimates of the weights of pyroclastic material and lava erupted by Parícutin Volcano from early 1943 to early 1952 have given a pyroclastic weight of some 2230 million metric tons and a lava weight of about 1330 million metric tons, making a total of 3560 million metric tons of solids. The weight of pyroclastic material ranged from a maximum daily average of more than 10 million metric tons in the first two weeks of eruption to a minimum of some 65,000 metric tons in 1951. The weight of lava ranged from a maximum daily average of about 650,000 metric tons in 1943 to a minimum of some 170,000 metric tons in the second half of 1950. The only period for which an estimate of the average daily weight of water vapor expelled by the Volcano could be made was the spring of 1945, when some 13,000 metric tons of water were expelled through the crater daily, besides some 500 metric tons contained in the lava extruded concurrently. Since the weight of pyroclastic material and lava erupted by Parícutin in the spring and summer of 1945 is estimated to have averaged about 1.2 million metric tons a day, the water expelled at that time amounted to about 1.1 pct of the total weight of material erupted. If the proportion of water had been nearly constant throughout the active life of the Volcano, the total weight of water would have amounted to some 39 million metric tons.
No abstract available.
No abstract available.
The lava flows of Parícutin Volcano, Mexico, offer an exceptional opportunity to study details of lava movement, because many flows are accessible throughout their length and can be watched from their birth to the cessation of their movement. Petrographically the lavas show no significant difference from one flow to another or in different parts of the same flow. The maximum lava temperature observed was 1070°C.; the maximum estimated rate of flow was 60 meters per minute; the viscosity is probably on the order of 10 5 to 10 6 poises. The flows start in fissure zones cutting older Parícutin lavas near the southwest base of the volcano. Within a short distance of its orifice a flow is covered with cooled blocks which are broken and slightly abraded as they are carried downstream. Differential movement in a flow takes place principally at its edges, where a reddish breccia and grooved and slickensided surfaces form. Like a glacier, a lava flow develops transverse crescentic ridges and lateral moraines. At its front movement is normally effected by the rolling forward of molten lava within, which carries down cooled blocks from the surface and piles them up ahead of the flow. As a flow dies the lava level lowers in the channel, and small side tongues break through the moraines. Some Parícutin lavas move considerable distances beneath older lava. The longest flow, which covered the town of San Juan in 1944, has a surface of rough curved slabs very different from the blocky surface of other flows but similar to the surface structures developed near lava orifices and by movement of viscous lava through fissures.
The activity of Parícutin varied greatly during the period April 12 to May 3. The strong eruptive activity that began in mid‐March, marked on March 17 by the formation of a new boca with a short‐lived volcancito and by external changes in the form of the cone, continued until April 18, The period April 12–18 was marked by bomb‐showers and explosive blasts at the rate of ten to 15 a minute, mostly from the south vent of the double crater. Most of the bombs fell into the north crater and on the north flank of the cone. From April 19 to 26 the activity was, in general, very weak, and little ash and few bombs were projected beyond the rim of the cone, Explosions were very rare, and the weak vapor column from the Volcano was accompanied by a dull surf‐like roar. Most of the vapor emerged from a small vent near the center of the divide between the two coalescing craters. A heavy ash column, at times approaching in intensity that of 1943, emerged from the Volcano from April 27 to 29. The ash was erupted from both the north and south vents of the crater, though the south vent is believed to have contributed the most. From April 30 to May 3 the activity was again very weak, and only a feeble column rose above the cone.