Dating lava flows for paleomagnetic
Type C eruptions last for months to years and produce small lava shields and many flows consisting of all three types.
Type D eruptions persist for decades to centuries and produce large lava shields and flow assemblages dominated by tube-fed pahoehoe.
Typically, variation rates are about 4 degrees/century, and dispersions are about 4.5 deg.
Principal sources of dispersion are imprecision in the 14 Cages (3.0 deg), local anomalies in the geomagnetic field (2.2 deg), and primary deformations of lava flows (1.7 deg).
Dating precisions are about 100 years during the past 500 years and about 250 years during the preceding millenium.
Precision should be increased to a few decades by reducing the dispersion, refining the history of variation, and adding paleomagnetic intensity to the record of variation.
The age windows obtained for these events encompass the true flow ages.
Two Type E eruptions large enough to produce extensive pyroclastic sheets have been followed by long intervals when most activity was confined to a summit caldera.
Rift activity waxed as summit activity waned, and in one example the waxing sequence resembles an evolutionary progression: Rift eruptions were at first brief and widely separated in time and space but gradually became frequent along a restricted segment of the rift zone and culminated in sustained activity at one locality.
Radiocarbon dates have been obtained for 30 charcoal samples corresponding to 27 surface lava flows from the Mauna Loa and Kilauea volcanoes on the Island of Hawaii. The new and revised C data set can aid hazard and risk assessment on the island.
The submitted charcoal was a mixture of fresh and archived material. The data presented here also have implications for geomagnetic modelling, which at present is limited by large dating errors.