A 400-k.y. perspective on arc volcanism: An exceptional explosive eruption record from Central Mexico
Volcanic eruption records provide key information for hazard planning but suffer from a time-dependent loss of resolution, hindering long-term evaluations of volcano behavior. Here, we investigate an exceptional sedimentary sequence from Lake Chalco, on the SE edge of Mexico City, which provides a perspective on volcanic activity over hundred-thousand-year time scales, and we develop a methodological and analytical protocol applicable to core datasets globally. The lava-dominated base of the sequence (~105 m) is followed by ~155 m of lateral-collapse derived deposits and overlain by ~295 m of lacustrine sediments containing at least 450 visible tephra fall deposits (TFDs), spanning 400 k.y. These TFDs include 205 events sourced from large-magnitude (predominantly volcanic explosivity index [VEI] ≥5) silicic explosive eruptions, principally from regional polygenetic sources, and 205 deposits from the nearby Sierra Chichinautzin volcanic field (SCVF). A gradual decline in both frequency and apparent magnitude in the silicic eruption record is consistent with the gradual migration of volcanism south along the adjacent Sierra Nevada volcanic range, toward Popocatépetl. In contrast, the SCVF-derived deposits imply persistent but episodic activity, on time scales of 40–70 k.y., suggesting that the SCVF has been more continuously active than previously recognized. Decoupled trends between the SCVF and regional silicic sources implies that the total magmatic flux is not dictated at the arc scale, or by external (e.g., climatic) drivers, but instead reflects the independent development of individual volcanic systems. The records indicate a minimum long-term frequency of impactful eruptions on Mexico City to be one per 900 years (>1 cm tephra deposited) or 9000 years (≥10 cm tephra).