Novel determination method of geochemical response time for volcanic activity monitoring

火山活动监测地球化学响应时间测定新方法

• 批准号: 1906305
• 负责人: Reika Yokochi
• 金额: $ 6万
• 依托单位: University of Chicago
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-05-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1906305&HistoricalAwards=false
• 关键词: Novel; determination; method; geochemical; response

Volcanic activities release elements from magma at depth into shallow underground fluids which seep as hot springs. Helium is an element highly enriched in magma, thus it can be easily detected as magmatic isotope signal in the hot spring water. The magmatic helium signal appears to respond to eruption cycles at some volcanos, but the association between its variation and observed volcanic activities is often indecisive, making it difficult to use as an eruption forecasting tool. In those studies, the temporal variations of the volcanic signals from hot springs were compared with the volcanic activities of time that the samples were collected. However, the volcanic signal may travel for substantial time period underground before seeping from the springs so that the volcanic signature we detect could reflect the magmatic activity of tens of years ago. In order to evaluate the time scale of the possible delay, the proposed project will determine the travel time of the shallow subsurface fluids that carry the magmatic helium signals using radioisotopes of Kr and Ar. Ontake and Unzen volcanos, Japan, were selected as candidate sites because of their relatively recent volcanic activities and abundant helium monitoring records. Radioisotopes of Kr and Ar will be analyzed by Atom Trap Trace Analysis (ATTA) at Argonne National Laboratory and by low level decay counting at University of Bern. The chronological information will be used for re-interpreting the relationship between local geotectonic activities and He isotope records as well as for assessing the possibility of recovering 'fossil' magmatic signatures. This is the first application of these novel tools to a volcanic aquifer system. This work will provide fundamental knowledge to evaluate the feasibility of forecasting volcanic eruptions using geochemical tracers including helium. Two students will be trained in the international fieldwork and laboratory work.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

火山活动将岩浆中的元素释放到浅层地下流体中，这些流体作为温泉渗出。氦是一种在岩浆中高度富集的元素，因此在温泉水中很容易被检测到作为岩浆同位素信号。岩浆氦信号似乎对某些火山的喷发周期有反应，但其变化与观测到的火山活动之间的关联往往是不确定的，因此很难用作火山喷发预测工具。在这些研究中，将来自温泉的火山信号的时间变化与收集样品时的火山活动进行了比较。然而，火山信号可能在地下传播了相当长的一段时间，然后才从泉水中渗出，因此我们检测到的火山信号可以反映数十年前的岩浆活动。为了评估可能延迟的时间尺度，拟议项目将使用Kr和Ar的放射性同位素确定携带岩浆氦信号的浅层地下流体的旅行时间。日本的Ontake和Unzen火山被选为候选地点，因为它们相对较新的火山活动和丰富的氦监测记录。Kr和Ar的放射性同位素将在阿贡国家实验室通过原子阱痕量分析（ATTA）进行分析，并在伯尔尼大学通过低水平衰变计数进行分析。年代学信息将用于重新解释当地的大地构造活动和He同位素记录之间的关系，以及评估恢复“化石”岩浆签名的可能性。这是这些新工具首次应用于火山含水层系统。这项工作将提供基础知识，以评估使用包括氦在内的地球化学示踪剂预测火山爆发的可行性。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。