Measurements of the inclination of the SE-03 Borehole on Surtsey Volcano

The inclined SE-03 borehole drilled in 2017 provides a unique opportunity to further examine the stratigraphy and submarine structure of Surtsey. The borehole was drilled towards west (azimuth 264°) with inclination of 35° from vertical. Downhole measurements conducted in August 2021 using a STP-8 inclinometer confirmed that any discrepancy in the orientation of the borehole is minor and does not affect the overall interpretation of the location of the SE-03 drill core. The average inclination of the borehole from vertical is 33.4±0.2°. The bottom of the borehole at 354.05 m measured depth corresponds to a total vertical depth of 294.7±1.2 m. This is 4.7 m deeper than the designed borehole path. The horizontal length from the well head to the point vertically above the bottom of the borehole is 195.1±1.0 m, which is about 8 meters less than the designed borehole path (203.1 m). Correcting for this 1.4-1.8° discrepancy between the planned inclination and the actual value gives greater accuracy in the location of the units cored. The results confirm the location of an intrusion directly beneath the Surtur crater, considered to be the feeder dyke for its eruption in 1966-67.