Ascent and eruption at the Albuquerque Volcanoes: A physical volcanology perspective
L. S. Crumpler
The Albuquerque volcanic field (AVF) erupted 1 km3 of lavas, averaging 1.5 m thick, and covering an area of 62 km2. Eruptions occurred from a minimum of two en echelon dikes segmented from a much larger dike and relayed from a minimum depth of 12 km. The anomalously thick lava section exposed at Mesa Prieta at the southern end of the field is consistent with lavas ponded within the confines of an early graben resulting from nearsurface deformation above the upward-propagating dike tip. Other graben and faults along the Ceja Mesa, if not tectonic, could be of similar dike-induced origin. Most of the apparent early sheet-like lava flows actually consist of numerous flow lobes, the margins of which are exposed as periodic breaks in the section along cliffs. In section, most of the flows bear systematic patterns of vesicle zonation interpreted to reflect steady growth of vesicles as solidification propagated inward from the upper and lower lava surfaces. Vesicle-free zones in some lava sections probably represent the effects of local lava flow inflation. Streamlined tumuli such as those distributed over the surface of earlier lavas formed when deflation left behind local pillars and tumuli that were subsequently engulfed by the overlying flow unit. The lengths of lava flows and morphology of lava flow channeling consistent with Gratz behavior enable estimation of effusion rates which range from 15 m3 s-1 in the earlier phases of eruption to 0.3 m3 s-1 during eruptions from the later stages at the principal cones. These are values typical of Hawaiian fissure erup- stions. Unlike Hawaiian eruptions, the AVF was supplied by a single deep dike, and exhibited a monotonically decreasing volume rate with time. The morphology of pyroclastic deposits allows qualitative estimates of the relative contributions of gas content and volume flux. Initial events were dominated by high gas and high volume flux and optically thick fire fountains. As volume flux declined, eruptions evolved to higher relative gas contents, moderate explosive activity, and accumulation of coarse, poorly welded agglomerate and spatter, and rootless flows. The steady progression from early long lava flows to late short lava flows reflects a secular drop in magma driving pressure within the feeding dike. Driving pressure continued to fall until it was unable to overcome the yield strength of magmas and pyroclasts filling the upper part of the vents, even though fresh magmas remained within the lower parts of the feeding dike. Eventual accumulation of additional volatiles enabled development of pressures sufficient to exceed the yield strength, resulting in deformation, cracking, and local sector sliding of cone flanks. This was followed by late explosive destruction of portions of Vulcan cone, and an anomalously high volume rate (~100 m3 s-1 ) and shorted-lived effusion that flowed down the western flank where it temporarily ponded.
- Crumpler, L. S., 1999, Ascent and eruption at the Albuquerque Volcanoes: A physical volcanology perspective, in: Albuquerque Country, Pazzaglia, Frank J.; Lucas, S. G.; Austin, G. S., New Mexico Geological Society, Guidebook, 50th Field Conference, pp. 221-233.