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

Abstract

Pahoehoe toe dimensions, morphology, and branching relationships were analyzed 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 regions within flow fields dominated by networks of pahoehoe toes, measurements of toe length, width, thickness, and orientation were completed for 445 toes at 13 sites. Variations in site characteristics, including slope, substrate, and position in the flow field allow an evaluation of the effects of such parameters on toe dimensions. Toe surface morphology (ropy or smooth), local flow lobe position (interior or margin), and connective relationships between toes were documented in the form of detailed toe maps. These maps show the number of branches connecting a given toe to other toes in its local pahoehoe network and illustrate branching patterns. Statistical analyses of toe dimensions and comparisons of pahoehoe toe study sites and sub-populations combined with field observations, evaluation of toe maps, and qualitative 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 widths greater than mean thicknesses (19 cm); sites that have mean widths greater 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 number of branches than smooth toes, and toes with three or more branches have greater lengths, widths, and thicknesses than toes with two or fewer branches, suggesting concentration of flow in these toe types. (d) The skewness of all size distributions of toe length and width to larger values suggests that toes are transitional to larger sheets and channels, consistent with field observations; and (e) Two distinct types of branching patterns (called monolayer and centrally ridged) were observed in preserved pahoehoe flow lobes. The significant variability in measured toe dimensions at Mauna Ulu suggests that toe dimensions are influenced by numerous locally defined, random factors, and that an approach based on stochastic methods can be used to model pahoehoe flow emplacement.

Mapping lava flows from Nyamuragira volcano (1967–2011) with satellite data and automated classification methods

“…Knowledge of the geographical position and direction of flows is used in hazard prediction (Trusdell 1995). Lava volumes can be estimated through either a combination of lava flow area with field-based lava flow thickness measurements (Shaw and Swanson 1970;Self et al 1997;Crown and Baloga 1999) or subtraction of pre-and post-eruptive digital elevation models (DEMs) (Rowland et al 2003;Lu et al 2004). These volumes can be used in magma supply models and time-series analyses of volcanic activity to further the understanding of eruption mechanisms (Burt et al 1994).…”

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

“…Within a given local network these features may occur at high angles to the overall downflow direction defined by the path from the vent to the flow field terminus. The increased variability in flow orientation at smaller scales is due to the higher relative variability in topography at the scale of toes compared to channels [Crown et al, 1998. Earlier studies had suggested that pahoehoe flow eraplacement is fractal in nature based .on measurements of flow margins [Bruno et al, 1992[Bruno et al, , 1994].…”

“…On the basis of measurements of sizes and orientations of individual pahoehoe features, recent analyses indicate that toes (tens to hundreds of centimeters) are gradational to small channels and sheets (1 to tens of meters) [Crown and 8aloga, 1999] and that emplacement processes within pahoehoe flows exhibit scale-dependent tendencies [Crown et al, 1998. Orientations of pahoehoe features (i.e., toes and channels) within the Mauna Ulu flow field display greater variability at small scales.…”

“…Differences between the two lava types result from P-type pahoehoe experiencing a longer storage time within the lava tube system, resulting in a greater degree of bubble coalescence and volatile loss prior to eraplacement. [Byrnes and Crown, 1998]. Inflation, vertical growth due to continued influx of lava beneath the surface crust, is most significant in portions of the flow field that have relatively horizontal (<2 ø ) underlying slopes but occurs to various extents throughout the medial and distal portions of a flow field Hon et al, 1994].…”

Plateaus and sinuous ridges as the fingerprints of lava flow inflation in the Eastern Tharsis Plains of Mars

“…Crown and Baloga (1999) find that at the meter scale lava toes tend to be greater in length than width except on low slopes where toes tend to spread laterally and can have higher widths than lengths. Crown (1999, 2000) find that at the flow field scale (N10 m) flows do not consistently widen on shallower slopes across the Hawaiian plains but conclude that topographic influences control the final width of a lava flow.…”