Development, Structure, and Behavior of a Perched Lava Channel at Kīlauea Volcano, Hawaiʻi, During 2007

Channelized lava flows are commonly produced during the early stages of basaltic eruptions. These channels usually maintain their morphology until the eruption ends or discharge is diverted. In some instances, narrower channels can roof over, developing into lava tubes. We report here on a channelized flow erupted at K (i) over bar lauea volcano in 2007 that evolved into a "perched lava channel" composed of a string of interconnected, elongate lava pools, forming a lava channel/lava pool hybrid. The lava channel, which had a time-averaged discharge rate of similar to 3-9 m(3)/s, initially fed a series of flow branches that exhibited cooling-limited and volume-limited controls on flow length, sometimes with each process controlling a different morphological aspect of a single flow branch. The perched lava channel grew vertically primarily by overplating of the channel levees from frequent overflows, forming a compound flow field. This vertical growth only occurred when the distal end of the channel was blocked. When levee failure at the distal end of the channel caused the lava level in the channel to drop below the levee rim, no vertical growth occurred. Seeps of spiny lava and slabby p (a) over bar hoehoe were common, erupting from uplift scarps on the channel levees, apparently fed by sills from denser, relatively crystal-rich material filling the bottom of the channel. We infer that lava in the channel was stratified in vesicularity and velocity, with foamy, vesicular, faster-moving lava at the top of the lava stream and denser, relatively outgassed, slower-moving lava filling the bottom of the channel. The channel levees were unstable, failing on several occasions, perhaps triggered by the levee seeps. The appearance of seeps, therefore, is one way of assessing the collapse potential of similar perched lava structures.