ANALYSIS OF CINDER SIZE DISTRIBUTION AND PROPERTIES TO INTERPRET ERUPTIVE HISTORY AND EROSION OF THE "SPLIT CINDER CONE" (CINDER HILL) IN DEATH VALLEY, CALIFORNIA

The southern Death Valley (DV) fault zone displays abundant evidence of late Quaternary volcanism and tectonism, which are well demonstrated by Cinder Hill, a small cinder cone that is split by two faults with a total right-lateral offset of a few hundred meters. The cone has yielded a K-Ar age of 0.69 Ma and has been interpreted as being fed by the DV bright spot via the Wingate Wash fault zone. Cinder chemistry has been reported as alkaline enriched with evolved Mg numbers that show a transition to trace-element-enriched hawaiites associated with waning volcanism.

In order to interpret details of the development of the cinder cone and distinguish original airfall clast distribution from fluid- and gravitational-driven sorting during post-eruption erosion, we measured three transects radiating at 0, 120, and 270 degrees from the highest elevation of each of the two offset parts of the cinder cone. Clast diameter, color, composition, and texture were determined for each cinder on the surface along each transect. Handheld x-ray fluorescence (XRF) was used to determine elemental composition.

Initial visual observations showed that the dominant cinder colors are red and black and the most common textures are aphanitic and vesicular. Application of the principle of superposition suggests that the black cinders represent an older phase of eruptive behavior, while red cinders are the youngest.

We collected data for over 3,300 surficial clasts. Using the graphical method for particle size determination, we found that the distribution of the whole clast population has a mean diameter of -5.8 phi, a standard deviation of 1.64 phi (poorly sorted), a skewness of -0.064 (near symmetrical), and a kurtosis of 0.96 (mesokurtic). Unpaired t-tests show a significant difference between mean particle sizes of black clasts and red clasts, as well as a significant difference between mean particle sizes of aphanitic and vesicular clasts. XRF results show no substantial differences between elemental abundances of red and black cinders. Cinder diameter is generally pebble sized (~-3 phi) at the summits of the hills and increases to include cobble and boulder sized clasts with distance downslope until reaching the toe, where clast size varies. There is no apparent correspondence between clast diameter and drainage channel position on slopes.