Models of Hawaiian volcano growth and plume structure: Implications of results from the Hawaii Scientific Drilling Project

The shapes of typical Hawaiian volcanoes are simply parameterized, and a relationship is derived for the dependence of lava accumulation rates on volcano volume and volumetric growth rate. The dependence of lava accumulation rate on time is derived by estimating the eruption rate of a volcano as it traverses the Hawaiian plume, with the eruption rate determined from a specified radial dependence of magma generation in the plume and assuming that a volcano captures melt from a circular area centered on the volcano summit. The timescale of volcano growth is t 2R/Vplat e where R is the radius of the melting zone of the (circular) plume and Vplat e isthe velocity of the Pa, cific plate. The growth progress ofa volcano can be described by a dimensionless time t = tVplate/2R , where t' = 0 is chosen to be the start of volcano growth and t' = 1 approximates the end of "shield" growth. Using a melt generation rate for the whole plume of 0.2 km3/yr, a plume diameter of 50 km, and a plate velocity of 10 cm/yr, we calculate that the lifetime of a typical volcano is 1000 kyr. For a volcano that traverses the axis of the plume, the "standard" dimensions are a volume of 57,000 km 3, a summit hickness of 18 km, a summit elevation of 3.6 km, and a basal radius of 60 km. The volcano first breaches the sea surface at t' • 0.22 when it has attained only 5% of its eventual volume; 80% of the volume accumulates between t' = 0.3 and t' = 0.7. Typical lava accumulation rates start out over 50 m/kyr in the earliest stages of growth from the seafloor, and level out at -35 m/kyr from t' • 0.05 until t' = 0.4. From t' = 0.4 to t' = 0.9, the submarine lava accumulation rates decrease almost linearly from 35 m/kyr to -0; subaerial accumulation rates are about 30% lower. The lava accumulation rate is a good indicator of volcano age. A volcano that passes over the plume at a distance 0.4R off to the side of the plume axis is predicted to have a volume of about 60% of the standard volcano, a lifetime about 8% shorter, and lava accumulation rates about 15-20% smaller. The depthage data for Mauna Kea lavas cored by the Hawaii Scientific Drilling Project are a good fit to the model parameters used, given that Mauna Kea appears to have crossed the plume about 15-20 km off-axis. The lifetime of Mauna Kea is estimated to be 920 kyr. Mauna Loa is predicted to be at a stage corresponding to t' • 0.8, Kilauea is at t' • 0.6, and Loihi is at t' • 0.16. The model also allows the subsurface structure of the volcanoes (the interfaces between lavas from different volcanoes) to be modeled. Radial geochemical structure in the plume may be blurred in the lavas because the volcanoes capture magma from a sizeable cross-sectional rea of the plume; this inference is qualitatively born out by available isotopic data. The model predicts that new Hawaiian volcanoes are typically initiated on the seafloor near the base of the next older volcano but generally off the older volcano's flank.