HR: 1340h
AN: V43B-1424    [Abstracts]
TI: HSDP II Drill Core: Preliminary Rock Strength Results and Implications to Flank Stability, Mauna Kea Volcano
AU: * Thompson, N
EM: thomps45@unr.nevada.edu
AF: University of Nevada, Reno, Department of Geological Sciences and Engineering, MS 172, Reno, NV 89557 United States
AU: Watters, R J
EM: watters@mines.unr.edu
AF: University of Nevada, Reno, Department of Geological Sciences and Engineering, MS 172, Reno, NV 89557 United States
AU: Schiffman, P
EM: schiffman@geology.ucdavis.edu
AF: University of California, Davis, One Shields Avenue, Davis, CA 95616 United States
AB: Selected portions of the 3-km HSDP II core were tested to provide unconfined rock strength data from hyaloclastite alteration zones and pillow lavas. Though the drilling project was not originally intended for strength purpose, it is believed the core can provide unique rock strength insights into the flank stability of the Hawaiian Islands. The testing showed that very weak rock exists in the hyaloclastite abundant zones in the lower 2-km of the core with strength dependent on the degree of consolidation and type of alteration. Walton and Schiffman identified three zones of alteration, an upper incipient alteration zone (1080-1335m), a smectitic zone (1405-1573m) and a lower palagonitic zone from about 1573 m to the base of the core. These three zones were sampled and tested together with pillow lava horizons for comparison. Traditional cylindrical core was not available as a consequence of the entire core having been split lengthwise for archival purposes. Hence, point load strength testing was utilized which provides the unconfined compressive strength on irregular shaped samples. The lowest unconfined strengths were recorded from incipient alteration zones with a mean value of 9.5 MPa. Smectitic alteration zones yielded mean values of 16.4 MPa, with the highest measured alteration strengths from the palagonite zones with a mean value of 32.1 MPa. As anticipated, the highest strengths were from essentially unaltered lavas with a mean value of 173 MPa. Strength variations of between one to two orders of magnitude were identified in comparing the submarine hyaloclastite with the intercalated submarine lavas. The weakest zones within the hyaloclastites may provide horizons for assisting flank collapse by serving as potential thrust zones and landslide surfaces.
DE: 8499 General or miscellaneous
DE: 5114 Permeability and porosity
DE: 5194 Instruments and techniques
DE: 5199 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting