Investigating the relationships among subduction character, volatile cycling, and eruptive activity along the Aleutian Arc

阿留申火山弧从阿拉斯加大陆到俄罗斯堪察加半岛绵延约4,000公里，将北面的白令海和南面的太平洋分开。 该火山弧是大约145座火山的家园，其中52座在历史上曾爆发过。 这些火山的喷发活动范围从连续的小爆发到巨大的爆发，如1912年在卡特迈发生的火山爆发。阿留申岛弧的火山活动是太平洋板块俯冲到北美板块之下的结果。在此过程中，沉积物和海洋地壳中锁定的水、碳和氮等挥发性元素缓慢转移到阿留申弧火山深处。 在高压下，挥发物被挤出俯冲板块进入上覆（地幔）区域，在那里它们帮助熔化岩石并产生岩浆。 与周围岩石相比，岩浆和挥发物的密度较低，使这些流体能够上升到地球表面，岩浆最终通过火山活动喷发，气体被释放到大气中。 虽然众所周知，挥发物在产生岩浆和影响喷发爆炸性方面发挥着重要作用，但目前尚不清楚挥发物的来源（俯冲板块、地幔和地壳）和随时间释放的挥发物数量（例如，其通量）如何影响火山喷发的规模、爆炸性和频率。该项目的目的是限制挥发性俯冲和释放的过程中，通过火山作用在研究不足的阿留申群岛西部，并提供火山活动的见解。阿留申火山弧的西部和中部是研究俯冲角度、俯冲速率和沉积物成分对岩浆生成和挥发分通量影响的理想地点。俯冲速率和沉积物通量增加沿着弧从基斯卡，最西部的火山，克利夫兰，位于弧的中心区域。此外，阿留申中部火山的历史喷发次数似乎比阿留申西部火山的要多。通过先前的考察，在阿留申群岛西部的五座火山收集了火山气体样本、气体排放测量和爆发性喷发的熔岩样本。通过该项目，将分析这些样品的化学和同位素组成，并将使用测量结果计算二氧化碳、二氧化硫、氮和水向大气的通量。从以前的研究俯冲到阿留申弧的材料的数量和类型的限制将进行比较的挥发性和熔岩输出的组成，以及挥发物的总通量在这里测量，提供洞察挥发性循环和岩浆生成。这些信息将与每座目标火山喷发规模、类型和频率的历史数据进行比较，以确定俯冲特征与火山活动之间可能存在的联系，最终帮助改进喷发预测和减灾工作。

The Aleutian Volcanic Arc stretches about 4,000 km from mainland Alaska to Kamchatka, Russia, separating the Bearing Sea to the north and the Pacific Ocean to the south. The arc is home to about 145 volcanoes of which 52 have erupted in historic time. The eruptive activity of these volcanoes ranges from continuous small explosions to devastatingly large eruptions such as the one that occurred at Katmai in 1912. Volcanic activity in the Aleutian Arc is a result of subduction of the Pacific plate beneath the North American plate. During this process, volatile elements such as water, carbon and nitrogen that are locked up in the sediments and oceanic crust are slowly transferred into the region deep under the Aleutian Arc volcanoes. Under high pressure the volatiles are squeezed out of the subducting plate into the overlying (mantle) region, where they help to melt rock and generate magma. The lower density of the magma and volatiles compared to the surrounding rock allows these fluids to ascend to the Earth's surface where the magma ultimately erupts through volcanism and the gases are released to the atmosphere. While it is well-known that volatiles play a significant role in both generating magma and influencing eruption explosivity, it is currently not well understood how the source of volatiles (subducted plate, mantle and crust) and the amount of volatiles released over time (e.g. their flux), may influence volcanic eruption size, explosivity and frequency. This project aims to constrain the process of volatile subduction and release through volcanism in the poorly studied Western Aleutians, and to provide insight into volcanic activity. The Western and Central portions of the Aleutian Volcanic Arc are the ideal locations to investigate the influence of subduction angle, rate and sediment composition on magma generation and volatile flux. The subduction rate and sediment flux increases along the arc from Kiska, the western-most volcano, to Cleveland, located within the central region of the arc. Additionally, the number of historic eruptions within Central Aleutian volcanoes appears to be greater in number than compared to the Western Aleutian volcanoes. Through a previous expedition volcanic gas samples, gas emission measurements and explosively erupted lava samples were collected at five Western Aleutian volcanoes. Through this project these samples will be analyzed for their chemical and isotopic composition and measurements will be used to compute the fluxes of carbon dioxide, sulfur dioxide, nitrogen and water to the atmosphere. Constraints on the quantity and type of material subducted into the Aleutian Arc from previous studies will be compared to the composition of volatile and lava outputs, as well as the total flux of volatiles measured here, to provide insight into volatile cycling and magma generation. This information will be compared to historic data on eruption size, style and frequency for each of the target volcanoes to identify possible links between subduction character and volcanic activity, to ultimately help improve eruption forecasting and hazard mitigation.