Abstract Since 1994 Popocatepetl volcano has extruded 85 lava domes, each of which has been destroyed by Vulcanian-style explosions. The paroxysmal Vulcanian explosion of 22 January 2001 has been unique by generating multiple pyroclastic density currents (PDCs). Scientists and Civil Protection authorities have used those PDCs to remap the high-risk hazard zone of the volcano, although little study has been carried out to understand the generation and evolution of those PDCs. Here, we examine 38 stratigraphic sections and analyze the granulometry, componentry, vesicularity, and petrology (glass, melt inclusions in plagioclase) of collected samples to interpret the origins of the Vulcanian explosions and the PDC behavior. The 22 January event generated two series of dense PDCs that detached from the base of the eruption column. The first set of PDCs traveled northwest across a glacier on the volcano, partially scouring and melting the ice that hours later generated a lahar. Two pulses of these PDCs were confined within a large ravine, surpassed the slope break, and traveled up to 3 km away from the vent. The deposits are matrix-supported throughout their extent. The second set of PDCs traveled to the northeast, mainly as unconfined currents that split into two lobes prior to the slope break. The farthest traveled current followed a western ravine and reached the forest 3.5 km from the summit. The eastern lobe buried a local hiking hut and reached 2.1 km. The deposits from these northeastern currents are massive and block-supported. All deposits (volume of 5.71 × 105 m3) have finger-like morphology with levees and frontal snouts. All PDCs flowed as a dense basal granular current with turbulent upper clouds at minimum speeds of 7–10 m/s. In terms of hazards, PDCs that interact with glaciers on the volcano are expected to travel farther and potentially generate extensive lahars. At present, small intermittent patches of glacier occur on the northern upper slopes of the volcano. The components of the deposits are, in order of abundance, black scoria (53–62 wt% SiO2), banded scoria, pumice (63 wt% SiO2), dome lithics (60–61 wt% SiO2), accidental lithics, and free crystals. Juvenile pumice and scoria contain phenocrysts of plagioclase (An47±10), clinopyroxene (En48±3), orthopyroxene (En64±1), ilmenite, and titanomagnetite set in a rhyolitic glass (pumice clast; 74.39 wt% SiO2) or microlite-rich matrix (scoria clast). The dome lithics also contain these phenocrysts as well as rare olivine phenocrysts (Fe2+/(Fe2 + Mg) = 0.1). Dissolved H2O-CO2 contents in melt inclusions hosted by pumice-plagioclase phenocrysts suggest the felsic magma was stored at depths of 2–4 km. Thus, the 2001 event was triggered by the injection of mafic magmas into a small volume of felsic magma, probably forming dikes left from the previous eruptive episode. We propose that the Vulcanian-explosions tap a column of magma (~2 km depth) equivalent to the volume that contained the felsic dikes. This mechanism has been acting during the destruction of all summit domes of the ongoing eruption of the volcano.

中文翻译：

---

2001 年 1 月 22 日波波卡特佩特火山（墨西哥）火山式爆炸产生的火山碎屑密度流的来源和行为

摘要 自 1994 年以来，波波卡特佩特火山已喷出 85 个熔岩圆顶，每个都被瓦肯式爆炸摧毁。2001 年 1 月 22 日的阵发性 Vulcanian 爆炸是独一无二的，它产生了多个火山碎屑密度流 (PDC)。科学家和民防当局已经使用这些 PDC 重新绘制了火山的高风险危险区，尽管很少有研究了解这些 PDC 的产生和演变。在这里，我们检查了 38 个地层剖面，并分析了收集到的样品的粒度、成分、水泡和岩石学（玻璃、斜长石中的熔融夹杂物），以解释 Vulcanian 爆炸的起源和 PDC 行为。1 月 22 日的事件产生了两个从喷发柱底部脱离的密集 PDC。第一组 PDC 向西北移动，穿过火山上的冰川，部分冲刷和融化冰层，几小时后产生了火山泥流。这些 PDC 的两个脉冲被限制在一个大峡谷内，越过斜坡断裂，并传播到距喷口 3 公里的地方。沉积物在其整个范围内都由基质支撑。第二组 PDC 向东北移动，主要是在斜坡断裂前分裂成两个瓣的无侧限流。最远的水流沿着西部峡谷到达距离山顶 3.5 公里的森林。东叶掩埋了当地的一个远足小屋，达到了 2.1 公里。来自这些东北流的沉积物是巨大的并且是块状支撑的。所有沉积物（体积为 5.71 × 105 m3）都具有指状形态，带有堤坝和额吻部。所有 PDC 都以致密的基底颗粒流的形式流动，上层云层湍流，最低速度为 7-10 m/s。在危害方面，与火山上的冰川相互作用的 PDC 预计会传播更远，并可能产生大量的火山泥流。目前，在火山的北部上坡出现小块间歇性冰川。沉积物的成分按丰度顺序为黑色矿渣（53-62 wt% SiO2）、带状矿渣、浮石（63 wt% SiO2）、圆顶岩屑（60-61 wt% SiO2）、意外岩屑和游离晶体。幼年浮石和矿渣含有斜长石 (An47±10)、单斜辉石 (En48±3)、斜方辉石 (En64±1)、钛铁矿和钛磁铁矿的斑晶，镶嵌在流纹岩玻璃中（浮石碎屑；74.39 wt% SiO2 富集）基质（火山渣碎屑）。圆顶岩屑也包含这些斑晶以及稀有的橄榄石斑晶 (Fe2+/(Fe2 + Mg) = 0.1)。由浮石-斜长石斑晶承载的熔体包裹体中溶解的 H2O-CO2 含量表明长英质岩浆储存在 2-4 公里的深度。因此，2001 年的事件是由将基性岩浆注入少量长英质岩浆引发的，这可能形成了前一次喷发事件留下的岩脉。我们建议，瓦肯尼爆炸产生的岩浆柱（约 2 公里深）相当于包含长英质岩脉的体积。这种机制在火山持续喷发的所有山顶圆顶被破坏的过程中一直在起作用。由浮石-斜长石斑晶承载的熔体包裹体中溶解的 H2O-CO2 含量表明长英质岩浆储存在 2-4 公里的深度。因此，2001 年的事件是由将基性岩浆注入少量长英质岩浆引发的，这可能形成了前一次喷发事件留下的岩脉。我们建议，瓦肯尼爆炸产生的岩浆柱（约 2 公里深）相当于包含长英质岩脉的体积。这种机制在火山持续喷发的所有山顶圆顶被破坏的过程中一直在起作用。由浮石-斜长石斑晶承载的熔体包裹体中溶解的 H2O-CO2 含量表明长英质岩浆储存在 2-4 公里的深度。因此，2001 年的事件是由将基性岩浆注入少量长英质岩浆引发的，这可能形成了前一次喷发事件留下的岩脉。我们建议，瓦肯尼爆炸产生的岩浆柱（约 2 公里深）相当于包含长英质岩脉的体积。在火山持续喷发的所有山顶圆顶被毁的过程中，这种机制一直在起作用。我们建议，瓦肯尼爆炸产生的岩浆柱（约 2 公里深）相当于包含长英质岩脉的体积。这种机制在火山持续喷发的所有山顶圆顶被破坏的过程中一直在起作用。我们建议，瓦肯尼爆炸产生的岩浆柱（约 2 公里深）相当于包含长英质岩脉的体积。这种机制在火山持续喷发的所有山顶圆顶被破坏的过程中一直在起作用。