![]() ![]() It appears to be one giant flow, but the flow field really consists of multiple small lobes of lava that flowed side by side down the floor of the valley. Most of the flow south of Highway 380 lies within the White Sands Missle Range. The Carrizozo lava flow field extends from its source a few kilometers north of the current Highway 380 southward to the extreme northern end of White Sands. ZimbelmanĪ few skylights occur in lava tubes along the traverse from the margins of the flow to the vent area (Little Black Peak). ![]() So the last material erupted was more pyroclastic. The last material probably was gas-rich and lava-volume-poor. As with the vent area of the McCartys lava flow in El Malpais, the vent cone of the Carrizozo lava flow represents the last activity at the location from which most of the lava flows were erupted. The vent area for the Carrizozo lava flow field, Little Black Peak. These results make the Carrizozo flow field the second youngest volcanism in New Mexico (Anthony et al., 1998), after only the McCartys flow field in western New Mexico. Cosmogenic (isotopic changes induced by exposure to high energy particles) studies indicate exposure ages of 4800 yrs (Anthony et al., 1998) to 5200 yrs (Dunbar, 1999) for the Carrizozo flow field. However, chemical analyses to date have revealed no evidence for distinct differences between the upper and lower lavas. Various researchers (e.g., Anthony et al., 1998 Dunbar, 1999) have distinguished between upper and lower Carrizozo flow units, separated by a narrow “neck” in the medial reach (Keszthelyi and Pieri, 1993). Its location and age is consistent with the regional volcanism elsewhere that is fundamentally associated with the Rio Grande rift (Renault, 1970 Faris, 1980 Anthony et al., 1998). The lava is intermediate in composition between alkalic and tholeiitic basalt. The entire flow covers ~330 km 2 to an estimated thickness of 10 to 15 m, for a total estimated erupted volume of ~4.3 km 3 (Allen, 1951). The Carrizozo flow field (Keszthelyi and Pieri, 1993) is 75 km long from the vent area to the distal margin in the Tularosa Valley (Zimbelman and Johnston, 2002). About the Sandia Mountain Natural History Center.Virtual Tour-Sayaka Ganz: Reclaimed Creations.Sensory Friendly Evenings at the Museum.Flows which begin as pahoehoe can convert to aa when a steep slope is encountered. The less common pahoehoe flows on these volcanos are erupted from vents on the gently sloping apron or the caldera floor. The steep slopes of the large western Galapagos volcanos thus generally consist of aa, making ascent very difficult (and occasionally painful!). Thus aa lavas are associated with high discharge rates and steep slopes while pahoehoe flows are associated with lower discharge rates and gentle slopes. Both magma discharge rate and the steepness of the slope over which the lava flows affect the flow rate. When a tear in the skin does form, it is readily healed. Under these circumstances, a well-developed skin can form which inhibits heat loss. Pahoehoe forms when lava flows more slowly. Sometimes the crust breaks in large plates, forming a platy aa. Bits of the crust are then tumbled in and coated by still liquid lava, forming the chunks. When the solid surface crust is torn by differential flow, the underlying lava is unable to move sufficiently rapidly to heal the tear. ![]() Under these circumstances, there is rapid heat loss and a resulting increase in viscosity. This difference in form reflects flow dynamics.Īa forms when lava flows rapidly. The surface of the aa flow consists of free chunks of very angular pieces of lava. The pahoehoe flow has a comparatively smooth or "ropy" surface. The older aa in the photo has weathered and the iron in it has oxided somewhat, giving it a reddish appearance (even young aa flows are occasionally slightly brown or reddish, due to the oxidation that occurs during flow). The difference in color is in this case is a reflection of age. The adjacent picture of a dark pahoehoe flow on a lighter brown aa flow illustrates the difference between the two (photo from Galapagos, Islands Lost in Time by T. A third type, pillow lava, forms during submarine eruptions. ![]() Both names, like a number of volcanological terms, are of Hawaiian origin. Lavas, particularly basaltic ones, come in two primary types: pahoehoe (pronounced 'paw-hoey-hoey") and aa (pronounced "ah-ah"). ![]()
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