Volcano Watch: How tephra deposits unlock the secrets of Kilauea volcano’s explosive past

Keanakako‘i Tephra from unit D in Kilauea south caldera wall; the lower portion of the tephra deposit has been smoothed with a scraper tool, making the surface look different from the portion above. a) finely laminated ash layers as well as a fine ash layer and a coarser layer with pumice grains, b) microscope photo of a dense, glassy ash grain from the fine lamination layers, c) microscope photo of a small pumice grain from the coarser layer, and d) well-preserved example of a fine ash layer with accretionary lapilli. (USGS photos by J. Schmith/Special to West Hawaii Today)

I go to the summit of Kilauea most weeks to study the extent, thickness, and physical characteristics of a 400- to 500-year-old tephra deposit, the product of explosive eruptions and part of what is called the Keanakako‘i Tephra. The total deposit is up to 10 meters (30 feet) thick along the southern wall of Kilauea caldera, but it was created by fragment upon fragment of tephra falling to the ground from volcanic plumes rising out of the caldera.