Abstract Long Valley Caldera has been restless since at least 1978. Prominent symptoms of this unrest include earthquake swarms and tumescence (inflation) centered on the resurgent dome. Over the years, interpretations of physical processes underlying this unrest have varied considerably. Results from a collection of geophysical studies infer the presence and/or active intrusion of magma in the crust. Geologic evidence, however, does not support recent magmatic activity in the caldera, leading to an interpretation that the caldera volcanic system is moribund, and the current unrest is a result of second boiling (aqueous fluids released during crystallization of the rhyolitic magma that produced the Bishop Tuff). Here, we examine the collective constraints provided by geophysical studies over the past four decades. Although the current geophysical evidence does not conclusively discriminate between unrest driven by recent crustal magmatic intrusion versus second boiling, it does provide evidence that a large volume of partial melt persists within the mid- and lower crust. This implies that the Long Valley Caldera system as a whole is long-lived, and the magma reservoir remains at least partially molten. In the shallow crust, the possibility of small pockets of magma remains. In aggregate, the data suggest commonality with other large, long-lived silicic caldera systems, such as Yellowstone and Campi Flegrei. Although the possibility of eruption within Long Valley Caldera remains unlikely, the geophysical evidence argues that Long Valley has an active magmatic system at depth and we must retain the possibility of eruptive hazards.

中文翻译：

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1978 年后加利福尼亚长谷火山口的膨胀：地球物理视角

摘要 Long Valley Caldera 至少自 1978 年以来一直处于动荡之中。这种动荡的突出症状包括地震群和以复苏的穹顶为中心的膨胀（通货膨胀）。多年来，对这种动荡背后的物理过程的解释有很大差异。一系列地球物理研究的结果推断岩浆在地壳中的存在和/或活跃侵入。然而，地质证据不支持火山口最近的岩浆活动，导致火山口火山系统垂死的解释，目前的动荡是第二次沸腾的结果（流纹质岩浆结晶过程中释放的水性流体，产生了主教塔夫）。在这里，我们研究了过去四年地球物理研究提供的集体约束。尽管目前的地球物理证据并不能最终区分由近期地壳岩浆侵入引起的动乱与第二次沸腾，但它确实提供了大量部分熔体持续存在于中下地壳的证据。这意味着长谷火山口系统作为一个整体是长期存在的，而且岩浆库至少保持部分熔融状态。在浅地壳中，仍有可能存在小岩浆袋。总的来说，数据表明与其他大型、长寿的硅质火山口系统具有共性，例如黄石和坎皮弗莱格雷。虽然长谷火山口内喷发的可能性仍然不大，但地球物理证据表明，长谷深部有活跃的岩浆系统，我们必须保留喷发危险的可能性。