Beyond a single-pulse eruption: paleomagnetic evidence for a multi-episode Youngest (74 ka) Toba Tuff

Abstract The Youngest (74 ka) Toba Tuff (YTT) super-eruption is traditionally interpreted as a single, short-lived event. However, new paleomagnetic data from both southern and northern non-welded exposures of YTT’s Units 2, 3, and 4 (in ascending order) challenge this model. Unit 2 samples were obtained from a thin ash layer sandwiched between two ignimbrites at two localities on the northern and southern sides of the caldera, whereas samples from Units 3 and 4 were collected from ignimbrites at one locality each on the southern side of the caldera. Mineral chemistry of matrix-glass and biotite from thin ash layers in both northern and southern deposits shows compositions consistent with YTT. Mean characteristic remanent magnetization (ChRM) directions from Units 3 and 4 are indistinguishable and consistent with those of the welded YTT. Mean ChRM directions of Unit 2 from two different localities are indistinguishable and exhibit a statistically distinct paleomagnetic direction from those of Units 3 and 4. Using a secular variation rate of 0.02 degrees/year, the estimated minimum time gap between Units 2 and 3–4 is ~ 807 ± 193 years. Temporal gaps recorded in non-welded proximal deposits are consistent with recent interpretations from distal marine tephra, suggesting that the YTT eruption was episodic and may have spanned several hundred to thousands of years. Graphical Abstract