Push core sampling at the Vance Segment
August 2, 2016
45o 33.7′ N 129o 55.4′ W
The goal of this dive was to sample the different flows from the valley of the eruptive axis of the Vance Segment toward the eastern flank of the South Rift of Axial Seamount. The Vance Segment is the next spreading ridge segment south of the one that Axial Seamount is on and overlaps with it in this area. Multibeam sonar bathymetry collected from ships suggests that enormous lava flows from Axial may have flowed many kilometers and partially filled the Vance valley with lava about 120 meters thick. Our mapping AUVs collected bathymetry of a portion of these flows just last week.
From east to west, the dive crossed large flows characterized by a high variation in sediment thickness. Push cores are used to collect sediment; radiocarbon dating of fossil shells from the base of the core after the cruise will give an age of those flows. This information is necessary for the reconstruction of the chronology of eruptions.
During the dive the thickness of the sediment provided an indication of the relative ages of the flows. Just to the west of the axis of the Vance Segment, a pillow lava flow was covered completely by sediment. A long push core on this flow revealed the sediments are about 110 centimeters thick. Flows with similar sediment thickness have been dated at about 40,000 years (we won’t have dates from these samples for many months). The western front of this flow is in direct contact with the voluminous flow the map shows initiated from the Axial rift zone farther west. It is a sheet flow covered by less than five centimeters of sediment, which suggests the flow may be younger than a thousand years.
—Morgane Le Saout