Event Location:

The Black Lab Pub
4100 Montrose
Houston, TX  77006

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Speaker: Will Sager, University of Houston

Tamu Massif is a submarine volcanic mountain with an area nearly that of New Mexico. Of that, there is no doubt. It is the largest edifice in the Shatsky Rise oceanic plateau, located ~1000 miles east of Japan. A quarter century ago, an interesting hypothesis was published, stating that oceanic plateaus formed from the voluminous, bulbous head of a starting mantle plume, which caused massive eruptions when the head rose to near the surface. A corollary was that oceanic plateaus are equivalent to continental flood basalts and that these eruptions built enormous volcanic piles. A quarter century ago, I noted that the magnetic anomaly over Tamu Massif looks like a classic equatorial dipole, modeling the mountain as a reversely-polarized homogeneous body and concluding that it formed rapidly during a single polarity period. This result seemed to fit the plume head hypothesis. More than a decade later, ocean drilling cores and seismic reflection profiles were interpreted to show that Tamu Massif is a single, central volcano, formed from massive lava flows, further supporting the plume head idea. The idea of a single volcano the size of New Mexico spawned the “world’s largest volcano” moniker and with click-bait journalism, the finding went viral. Among nagging doubts brushed aside, magnetic anomalies told a contradictory tale. Linear magnetic anomalies have been traced through much of Shatsky Rise and surround Tamu Massif. The indication is that the volcano formed near a spreading ridge triple junction during the Late Cretaceous. Spreading ridges are huge linear volcanoes, so how did an enormous single volcano form nearby? I went back in 2015 to collect new magnetic data over Tamu Massif. The resulting magnetic anomaly map shows that Tamu Massif and nearby Ori Massif (also a large volcanic mountain) are characterized by linear magnetic anomalies, similar to those formed at mid-ocean ridges. Only seafloor spreading creates such anomalies, so the implication is that Tamu Massif, and indeed all of the Shatsky Rise plateau, formed by this process. Tamu Massif is not an enormous single volcano, but instead a swollen segment of the past mid-ocean ridge system.

Speaker Biography: William Sager, University of Houston
William Sager is a professor in the Department of Earth and Atmospheric Sciences at University of Houston. After graduating from Duke University with a BS in physics, he obtained his MS and PhD degrees in geology and geophysics from University of Hawaii in 1979 and 1983, respectively. For 29 years, he worked at Texas A&M University before moving to University of Houston in 2013. His research focuses on marine geology and geophysics, especially with regard to plate tectonics. Dr. Sager has published 135 journal articles, sailed on 44 research cruises, and mentored >100 graduate students.

**There is no registration fee for our SIG meetings. Dinner and drinks are available from the establishment's menu. We ask that you continue to pre-register, to prepare meeting room set up.