Collaborative Research: 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延伸到俄罗斯堪察加半岛，绵延约4000公里，将北方的轴承海和南方的太平洋分开。这条弧线上有大约145座火山，其中52座在历史上曾经喷发过。这些火山的喷发活动范围从连续的小喷发到毁灭性的大喷发，比如1912年发生在卡特迈的那次。阿留申弧的火山活动是太平洋板块俯冲到北美板块之下的结果。在这个过程中，被锁在沉积物和海洋地壳中的挥发性元素，如水、碳和氮，慢慢地转移到阿留申弧火山深处的地区。在高压下，挥发物从俯冲板块中被挤压到上覆的地幔区域，在那里它们帮助融化岩石并产生岩浆。与周围的岩石相比，岩浆和挥发物的密度较低，这使得这些流体能够上升到地球表面，岩浆最终通过火山作用喷发，气体被释放到大气中。众所周知，挥发物在产生岩浆和影响喷发爆发性方面发挥着重要作用，但目前尚不清楚挥发物的来源（俯冲的板块、地幔和地壳）以及随时间释放的挥发物的数量（例如它们的通量）如何影响火山喷发的规模、爆发性和频率。该项目旨在限制在研究较少的西阿留申群岛的火山活动中挥发性物质的俯冲和释放过程，并提供对火山活动的深入了解。阿留申火山弧的西部和中部是研究俯冲角、俯冲速率和沉积物组成对岩浆生成和挥发通量影响的理想地点。从最西端的基斯卡火山到位于弧中心的克利夫兰火山，俯冲速率和沉积物通量沿弧增加。此外，与西阿留申火山相比，中阿留申火山的历史喷发次数似乎更多。通过之前的一次考察，在西阿留申群岛的五座火山收集了火山气体样本、气体排放测量值和爆炸喷发的熔岩样本。通过这个项目，将对这些样品的化学和同位素组成进行分析，并利用测量结果计算二氧化碳、二氧化硫、氮和水进入大气的通量。以前的研究对俯冲到阿留申弧的物质的数量和类型的限制将与挥发物和熔岩产出的组成以及这里测量的挥发物的总通量进行比较，以提供对挥发物循环和岩浆生成的深入了解。这些信息将与每个目标火山的喷发规模、风格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的可能联系，最终帮助改进喷发预测和减灾。

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.