The structure and emplacement of cinder cone fields

Terrestrial cinder cone fields generally occur in two types of volcanic provinces, either: (1) upon the flanks of major volcanoes, or (2) within relatively flat-lying volcanic fields. Measurements of cone shape and distribution have been performed in three volcano cone fields (Mauna Kea, Hawaii; Mt. Etna, Italy; Kilimanjaro, Tanzania) and three platform cone fields (San Francisco Mtn., Ariz.; Paricutin region, Mexico; Nunivak Island, Alaska). Modal average values of cone basal diameter are on the order of 300 to 400 m within volcano cone fields and 900 to 1000 m within platform cone fields. Cone height/diameter ratios are generally smaller within the platform cone fields. Variations in cone shape cannot be directly attributed to different eruption conditions, however, since cone morphometry is also a function of weathering environment and exposure age. Modal average values of cone separation distance range from 600 to 800 m within volcano cone fields to 1000 to 1200 m within platform cone fields. Comparison of average morphometric parameters for the six fields indicates that cone diameter is positively correlated with cone separation distance. Furthermore, the size (diameter) and spacing of cinder cones formed on the flanks of volcanoes is generally less than the size and spacing of cones constructed in volcanic fields. Historical observations indicate that flank eruptions commonly shift to higher or lower elevations in response to variations in magmatic pressure. Such shifts would tend to limit the growth of individual cones and would also result in smaller separation distances between cones. Comparable variations in vent location are less likely to occur within volcanic fields due to smaller regional topographic differences and the general lack of regional rift zones.