Pahoehoe toe dimensions, morphology, and branching relationships at Mauna Ulu, Kilauea Volcano, Hawai'i

Pahoehoe toe dimensions, morphology. and branching relationships were analy zed in flows emplaced during 1972 at Mauna Ulu. a satellitic shield on the east rift zone of Kilauea Volcano, Hawai'i. In order to characterize region s within flow fields dominated by networks of pahoehoe toes, measurements o f toe length, width, thickness, and orientation were completed for 445 toes at 13 sites. Variations in site characteristics, including slope. substrat e, and position in the flow field allow an evaluation of the effects of suc h parameters on toe dimensions. Toe surface morphology (ropy or smooth), lo cal flow lobe position (interior or margin), and connective relationships b etween toes were documented in the form of detailed toe maps. These maps sh ow the number of branches connecting a given toe to other toes in its local pahoehoe network and illustrate branching patterns. Statistical analyses o f toe dimensions and comparisons of pahoehoe toe study sites and sub-popula tions combined with field observations, evaluation of toe maps, and qualita tive examination of toe dimension size distributions show the following: (a ) Although there are significant variations at a given site, toes typically have mean lengths (101 cm) greater than mean widths (74 cm) and mean width s greater than mean thicknesses (19 cm); sites that have mean widths greate r than mean lengths are those with lower slopes. (b) Where significant site -to-site variations in mean values of a given toe dimension were apparent, these differences could not be directly related to site characteristics. (c ) Ropy toes have significantly larger mean values of length, width, and num ber of branches than smooth toes, and toes with three or more branches have greater lengths, widths, and thicknesses than toes with two or fewer branc hes, suggesting concentration of Row in these toe types. (d) The skewness o f all size distributions of toe length and width to larger values suggests that toes are transitional to larger sheets and channels, consistent with f ield observations: and (e) Two distinct types of branching patterns (called monolayer and centrally ridged) were observed in preserved pahoehoe flow l obes. The significant variability in measured toe dimensions at Mauna Ulu s uggests that toe dimensions are influenced by numerous locally defined, ran dom factors, and that an approach based on stochastic methods can be used t o model pahoehoe flow emplacement.