11:00 AM - 11:15 AM
[MGI31-02] Consolidation characteristics of offshore sediments in the Christiana, Santorini, and Kolumbo volcanic field, Greece (IODP Expedition 398)
Keywords:Excess pore fluid pressure, Slope instability, IODP Expedition 398, Santorini, Consolidation test
An abnormally rapid accumulation of volcaniclastics is expected in sedimentary basins around submarine volcanoes. This process can make the sedimentary basin unstable because the large increase in overburden leads to the generation of excess pore fluid pressure that can hinder the consolidation of sediments. Therefore, the consolidation state of the sediments is crucial information for assessing the slope instability around volcanoes.
IODP Expedition 398 cored marine sediments in the Christiana, Santorini, and Kolumbo (CSK) volcanic field in the Aegean Sea of Greece. We performed consolidation tests on mudstones and calcareous oozes just below the thick volcaniclastics in three basins (Anafi, Anydros, and Christiana Basin) situated around the Santorini caldera. Consolidation trends (void ratio vs. applied stress) show clear yield stresses which indicate the maximum consolidation stress of the sediments.
Consolidation yield stresses of the sediments were 1-2 MPa lower than the overburden at IODP Sites U1589 (Anydros Basin, 200-350 mbsf), U1590 and U1593 (10 km NW from the submarine Kolumbo caldera, 200-400 mbsf), and U1592 (Anafi Basin, ~300 mbsf). This implies that an excess pore fluid pressure of 1 to 2 MPa is generated in the sediments and prevents normal consolidation. All of the underconsolidated intervals are covered by volcaniclastics more than 200 m thick, which originate from the Santorini and Kolumbo volcanoes. Since the overburden of the volcaniclastics is approximately 2 MPa, the excess pore fluid pressure of 1 to 2 MPa could have been generated by the emplacement of the volcaniclastics. Therefore, the rapid sediment-supply (0.8-1.0 m/ky) from the submarine volcanoes apparently makes the surrounding sedimentary basins unstable.
On the other hand, measurements from IODP Site U1591 (i.e., Christiana Basin) and U1599 (i.e., Anafi Basin) show a normal consolidation state and the consolidation yield stress balances the overburden. These sites have a relatively thin cover of volcaniclastics (~100 m) above the non-volcanic sediments and the mean sedimentation rate is moderate (0.1-0.4 m/ky).
We compare the consolidation characteristics of the three basins and discuss their spatial-temporal variation in relation to the sedimentation rate and physical properties of the sediments.
IODP Expedition 398 cored marine sediments in the Christiana, Santorini, and Kolumbo (CSK) volcanic field in the Aegean Sea of Greece. We performed consolidation tests on mudstones and calcareous oozes just below the thick volcaniclastics in three basins (Anafi, Anydros, and Christiana Basin) situated around the Santorini caldera. Consolidation trends (void ratio vs. applied stress) show clear yield stresses which indicate the maximum consolidation stress of the sediments.
Consolidation yield stresses of the sediments were 1-2 MPa lower than the overburden at IODP Sites U1589 (Anydros Basin, 200-350 mbsf), U1590 and U1593 (10 km NW from the submarine Kolumbo caldera, 200-400 mbsf), and U1592 (Anafi Basin, ~300 mbsf). This implies that an excess pore fluid pressure of 1 to 2 MPa is generated in the sediments and prevents normal consolidation. All of the underconsolidated intervals are covered by volcaniclastics more than 200 m thick, which originate from the Santorini and Kolumbo volcanoes. Since the overburden of the volcaniclastics is approximately 2 MPa, the excess pore fluid pressure of 1 to 2 MPa could have been generated by the emplacement of the volcaniclastics. Therefore, the rapid sediment-supply (0.8-1.0 m/ky) from the submarine volcanoes apparently makes the surrounding sedimentary basins unstable.
On the other hand, measurements from IODP Site U1591 (i.e., Christiana Basin) and U1599 (i.e., Anafi Basin) show a normal consolidation state and the consolidation yield stress balances the overburden. These sites have a relatively thin cover of volcaniclastics (~100 m) above the non-volcanic sediments and the mean sedimentation rate is moderate (0.1-0.4 m/ky).
We compare the consolidation characteristics of the three basins and discuss their spatial-temporal variation in relation to the sedimentation rate and physical properties of the sediments.