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

Abstract

Lava flow field development at Mauna Ulu was analyzed by characterizing pahoehoe surface units and their distribution relative to pre-Mauna Ulu topography and the main lava tube system. Four pahoehoe surface units were identified 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 III), and irregular surfaces exhibiting meter-scale roughness, which typically occur as channels (unit IV). The distribution of these units was mapped on high-resolution aerial photographs using an automated supervised classification technique; Geographical Information Systems (GIS) analyses utilized digitized ∼6 m (20 foot) contour interval topography of the pre-Mauna Ulu surface and the mapped lava tube network to assess the influence of topography and lava tubes on the emplacement of surface flows. The four pahoehoe 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 correlation 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°) mean underlying slopes relative to those of the sheets of unit I (14.2°) and the toe networks representing units II (15.2°) and III (15.9°). The distribution of the four units does not appear to be directly related to their proximity to the largest scale of lava tubes, suggesting two possible scenarios: the main lava tubes do not significantly affect surface unit emplacement within the study area and/or these tubes do not preferentially emplace any of the four units identified in this study. Copyright 2001 by the American Geophysical Union.