The AD 260 Eruption at Lake Ilopango, El Salvador: A Complex Explosive Eruption Through a Caldera Lake

萨尔瓦多中部的VallanceIlopango火山口在过去的60,000年中至少四次猛烈喷发，产生了大范围的火山灰和炽热的火山灰流，最近一次是在公元260年。伊洛潘戈可能是中美洲最危险的火山中心，因为它可能发生猛烈的爆炸性喷发，而且靠近中美洲最大的城市圣萨尔瓦多。公元260年，炽热的火山灰流在萨尔瓦多高地蔓延，沿着陡峭的山谷席卷了40公里，到达太平洋沿海平原，这些地区当时是早期玛雅文明的居住地，现在人口稠密。火山灰横扫中美洲大部分地区，墨西哥南部大部分地区，以及太平洋和墨西哥湾附近的部分地区。火山喷发很可能是降临到中美洲文明头上的最大灾难。火山喷发的总体积为20~50立方公里，包括6个阶段：(1)初始落差和涌浪，(2)主普林尼期落差，(3)高能火山碎屑沉积，(4)深成落差，(5)层状硅质岩落差，(6)主要褐沸石。这项研究将表征对喷发方式和强度的控制，并区分岩浆的内在和外在因素。对复杂但独特的矿床地层学的研究将涉及火山学中的下列重要课题：普林尼亚火山喷发数值模型的现场校准、火山碎屑流和涌流的迁移和沉积机制，以及浅水爆炸喷发中的岩浆-水相互作用。这项研究的主要目标是更好地了解浅水爆炸性喷发的行为，特别是伊洛潘戈火山口在喷发周期中的行为。一个重要的次要目标是提高对萨尔瓦多火山过程及其相关危害的认识。

9903291VallanceIlopango caldera in central El Salvador erupted violently to produce widespread ashfalls and hot ash flows at least four times in the last 60,000 years, and most recently in AD 260. Ilopango is perhaps the most dangerous volcanic center in Central America because of its potential for violent explosive eruption and its proximity to San Salvador, the largest city in Central America. In AD 260, hot ash flows spread throughout the Salvadoran highlands and swept up to 40 km down steep valleys onto the Pacific coastal plain, areas then populated by early Mayan civilization and now densely populated. Ash fell across much of Central America, much of southern Mexico, and nearby parts of the Pacific Ocean and Gulf of Mexico. The eruption may well have been the greatest catastrophe ever to befall Meso-American civilization. The eruptives have total volume of 20 to 50 cubic km and encompass 6 stages: (1) initial fall and surges, (2) main Plinian fall, (3) energetic pyroclastic deposit, (4) phreatoplinian fall, (5) bedded phreatomagmatic fall, and (6) main ignimbrite. This study will characterize controls on eruption style and intensity and differentiate factors intrinsic and extrinsic to the magma. Study of the complex but distinctive stratigraphy of deposits will address the following important topics in volcanology: field calibration of numerical models for Plinian eruptions, transport and deposition mechanisms for pyroclastic flows and surges, and magma-water interactions in explosive eruptions through shallow water. The chief goal of the study is a better understanding of the behavior of explosive eruptions through shallow water and, specifically, that of Ilopango caldera during eruptive cycles. An important secondary goal is increasing awareness of volcanic processes and their affiliated hazards in El Salvador.