THE CARRIZOZO LAVA FLOW FIELD, NEW MEXICO: AN ASYMMETRIC LOW SHIELD AND IMPLICATIONS FOR STUDIES OF PLANETARY SMALL-VENT FIELDS

The Carrizozo lava flow field in New Mexico is among the largest recent basaltic eruptions with a volume of ~ 4.3km3 and a length of ~ 75 km. Past work inferred that it was emplaced via tubes and inflated sheets, although only indirect evidence of tubes was found. Here we discuss field work on the Carrizozo vent region, comprising a low shield ~ 7 by 5 km in diameter, rising up to 60 m above the pre-flow terrain. From the western flow margin, Differential Global Positioning System (DGPS) data show three topographic plateaus increasing to 2, 8, and 10 m, and possibly a fourth at 12 m, above the adjacent terrain across 1.2 km towards the vent. The discontinuous plateaus include lava collapse and rise pits. 30 m/pix Shuttle Radar Topography Mission (SRTM) and DGPS data show that plateaus are typified by <1 degree slopes, except across pit walls where slopes are steeper. SRTM derived slopes increase from 2 to 9 degrees across the next 1.3 km, rising 50 m above the plateau terrain to the summit. The near vent region is typified by more numerous collapse and inflation pits resulting in a less uniform plateau surface. The vent (Little Black Peak) is capped by a ~30 m tall cinder pile and small (~ 5 m) summit depression. Although Little Black Peak is the prominent summit feature, the vent area appears to comprise a set of three coalesced cinder piles and a perched lava pond. East of the main vent is a collapsed lava tube, exposing a network of three branching tubes that descend into the eastern flow field at different topographic levels. Lava flow textures and structures suggest that the Carrizozo low shield was built through a combination of several tube-fed sheet inflation events, breakouts resulting in small surface lava flows, and several mildly explosive episodes at the vent. The eruption also fed a much more extensive, likely tube-fed lava flow beyond the extent of the primary low shield for 10s of kilometers. Therefore, the bulk of the flow field is located beyond the extent of the Carrizozo low shield. Similar small-vents are seen in clusters on Mars and elsewhere on the Earth. The distribution of lava deposits at Carrizozo suggest that care should be taken when estimating low shield volume or surface area based on remote sensing data alone, particularly if the vent is located within a field of vents where embayment of extensive lava flow fields might have occurred.