Relationships between pahoehoe surface units, topography, and lava tubes at Mauna Ulu, Kilauea Volcano, Hawaii

Lava flow field development at Mauna Ulu was analyzed by characterizing pah oehoe surface units and their distribution relative to pre-Mauna Ulu topogr aphy and the main lava tube system. Four pahoehoe surface units were identi fied in the field and described on the basis of color, surface texture, and morphology: broad, flat sheets (unit I), networks of interconnected glassy -surfaced toes (unit II), late stage breakout lobes of viscous toes (unit I II), and irregular surfaces exhibiting meter-scale roughness, which typical ly occur as channels (unit TV). The distribution of these units was mapped on high-resolution aerial photographs using an automated supervised classif ication technique; Geographical Information Systems (GIS) analyses utilized digitized similar to6 m (20 foot) contour interval topography of the pre-M auna Ulu surface and the mapped lava tube network to assess the influence o f topography and lava tubes on the emplacement of surface flows. The four p ahoehoe units represent variations in emplacement conditions, on the basis of the various flow regimes (sheet, toe, and channel) and surface textures (smooth/glassy and rough) displayed. These surface units show a limited cor relation to pre-Mauna Ulu topography based on their mean underlying slopes. The higher flow rates indicated by the channelized surfaces of unit IV are spatially correlated with higher (22.2 degrees) mean underlying slopes rel ative to those of the sheets of unit I (14.2 degrees) and the toe networks representing units II (15.2 degrees) and III (15.9 degrees). The distributi on of the four units does not appear to be directly related to their proxim ity to the largest scale of lava tubes, suggesting two possible scenarios: the main lava tubes do not significantly affect surface unit emplacement wi thin the study area and/or these tubes do not preferentially emplace any of the four units identified in this study.