b'Carnegie Science|Fall 2020 17New Technique Images Beneath an Active Aleutian VolcanoThis photo shows the Cleveland Volcano in Alaskas central Aleutian Islands. It is one of the most-active volcanoes in the Aleutians.Image courtesy Cindy Werner, Alaska Volcano ObservatoryA novel approach to analyzing seismic data reveals deep vertical zones of low seismic velocity in the plumbing system underlying Alaskas Cleveland Volcano, one of the most active of the 70-some Aleutian volcanoes. Helen Janiszewski, recently with Carnegie and now at the University of Hawaii, Mnoa, and Carnegies Lara Wagner and Diana Roman published their findings in Scientific Reports.Arc volcanoes like Cleveland form over plate boundaries where one tectonic plate slides beneath another. They are linked to the Earths mantle by complex subsurface structures over the full thickness of the planets crust. These structures are more complexHelen Janiszewski (left), recently with Carnegie and now at the University of Hawaii, Mnoa, with Carnegies Lara Wagner (right, in second image) and Diana Roman (left, than the large chambers of molten rock shown in textbookin second image) published the findings in Scientific Reports. illustrations of a volcano. Rather, they comprise an interlaced arrayImages courtesy Carnegie Institution for Scienceof solid rock and a mushy mix of partially molten rock and solid crystals. activity, making imaging the architecture of the lower and Resolving this subterranean architecture is crucial formiddle crust below very challenging.emergency planning and saving human lives. But these regionsUntil now, the number of instruments needed to use seismic have been difficult to image. waves traveling from more-distant earthquakes for imaging was To visualize our planets interior, scientists have traditionallyprohibitive.used a variety of geophysical and geochemical approaches toJaniszewski demonstrated a novel technique that uses determine the structures beneath volcanoes. seismic waves coming from distant earthquakes but isolates just Seismic waves caused by earthquakes, for instance, can bethe part of them that is affected by moving through the boundary used like ultrasound to map the Earths interior. But for this to work,between the Earths mantle and crust. This allowed Janiszewski the waves must reach the subterranean structures of interest.to build models that better distinguish the partially molten Although Cleveland has frequent gas emissions, explosions, andregions from the surrounding solid rock in these difficult-to-ash deposits at its surface, there is little evidence of deep seismicreach depths beneath the Cleveland Volcano without requiring a much-more-extensive number of seismic stations at the surface.Unlike typical seismic imaging experiments that deploy Mid-Ocean Ridge dozens of seismometers, this study used only eight. Six of these stations were deployed as part of the National Science Foundation-funded Islands of the Four Mountains experiment Def Vol between August 2015 and July 2016. Two were permanent Alaska ormati canic Volcano Observatory stations.on Ar We revealed the volcanos deep subterranean structure in Fro cnt never-before-seen detail, using fewer instruments by an order of magnitude than is typical for detailed seismic imaging at Continental Crust volcanoes, Janiszewski said. The Lithosphere Oc technique will allow imaging of ean Mantleic Wedge structures underneath volcanoesSUPPORT:AsthenosphereCrust where there are only a few stations,The National Science Foundation or where a lack of deep earthquakesGeoPRISMS program [grant Arc volcanoes, such as Alaskas Cleveland, form over subduction zones, boundaries whereEAR-1456939 to DCR] and the in the vicinity makes other methodsAlaska Volcano Observatory one tectonic plate slides beneath another, as shown above. supported this work.Image courtesy Roberto Molar Candanosa, Carnegie Institution for Science difficult, she added.'