DON SWANSON AND KILAUEA'S FAR-TRAVELED LITHIC BLOCKS (Invited Presentation)

Large parts of Kīlauea’s south flank are underlain by a ~200 BCE pāhoehoe substrate, and scattered vestiges of the five-unit Kulanaokuaiki Tephra, erupted between 400 and 1000 CE, remain on this surface. The third of these five deposits, K-3, consists mostly of scoria lapilli but this unit is also associated with lithic blocks, the largest of which have diameters greater than the thickness of associated K-3 scoria deposits. Much of the K-3 scoria has been eroded away, leaving blocks and lithic lapilli as lag clasts on the pre-K-3 surface.

A new strategy was required to quantify the distribution of these widely scattered clasts. Don established a 110-node network defining collection sites separated by ~700m. He then adopted an 18-minute search routine that normalized collection durations and provided ample time to locate the scattered lag lithics. Visiting each of these 110 nodes, he collected the ten largest clasts, photographed them in the field, and returned all 1100 of them to HVO for future study. The isopleth map resulting from this work shows that dense, 8-12 cm blocks were dispersed 9-10 km southeastward from the interpreted summit vent, an anomalous direction at a high angle to prevailing northeast trade winds. In addition, largest clast diameters decrease toward the southeast, indicating that these clasts were not dispersed ballistically. These findings led to the interpretation that these lithic clasts were entrained in a powerful jet, likely powered by steam or CO₂, that carried them to jet stream altitudes (4-17 km), where prevailing winds of 20-50 m/s deflected their rise and fall toward the southeast.

 

These accomplishments are good examples of how Don’s field-geology expertise, plus a large measure of hard work, has led to new volcanological understandings. Specifically, it is now realized that Kīlauea can erupt far more energetically than anyone dared to imagine.