Trace element (TE) ratios of convergent-margin magmas have been found to vary systematically with arc crustal thicknesses. Here we use statistical smoothing techniques along with Sr/Y and La/Yb trace element Moho depth proxies to determine crustal thickness along the volcanic front for three arc segments: the Central Volcanic Zone of the Andes arc, the Central America arc at Nicaragua and Costa Rica, and segments of the Alaska-Aleutian Islands arc (northwesternmost USA). The results are comparable to those from seismic surveys. TE depth proxies give ~70 km crust thickness beneath the Central Volcanic Zone's Altiplano region and show thinner crust (60 km for La/Yb, 43 km for Sr/Y) as the volcanic line crosses into the Puna region. In Central America, the proxy analyses show crustal thickness changes between the Chorotega block and the Nicaragua depression, with both proxies agreeing for Nicaragua (~27 km) but with La/Yb giving considerable thicker (~45 km) crust than Sr/Y (~30 km) for Chorotega. For these two arc segments, the La/Yb proxy approximated the seismically inferred Moho depth to within 10 km for the entire profile, but the Sr/Y proxy-estimated crustal thicknesses diverge from those of the La/Yb proxy and seismic methods in the thin-crust regions. For the Alaska-Aleutian arc, both TE proxies indicate that crust varies from thick (~35 km) for the western Aleutian segment (175°E to 175°W), to thin (~22 km) for the transitional segment (175°W to 158°W), to thick (35+ km) for the eastern Alaska Peninsula (158°W to 150°W). Geophysical estimates favor a crustal thickness of 30-40 km for the same region. We propose that statistically treated geochemistry-based proxies can provide useful estimates of crustal thickness when estimates from Sr/Y and La/Yb agree. We investigated the disagreement in the Alaska-Aleutian case in more detail. Alaska-Aleutian crustal thickness was found to correlate with calc-alkaline (CA) versus tholeiitic (TH) segments of the arc, as represented by along-arc smoothing of the volcanoes' CA-TH indices. The thin crust of the transitional segment trends TH while the thicker crust of the flanking segments trend CA. We find that crustal thickness also plays a role in inferred magma flux (here approximated by volcano volume), with greater flux associated with thinner crust. Thin crust beneath the Alaska-Aleutian transitional segment may reflect continuing loss of cumulates from the lower crust and/or lithospheric mantle into the asthenosphere, leading to enhanced melting beneath this region.

Today's undergraduate students are accustomed to animations as impor tant to their learning. Complex geologic processes such as subduction are well suited to animation. In spite of this opportunity and need, highquality animations of fundamental Earth processes are uncommon. We have pro duced a realistic animation of plate creation and destruction processes for the undergraduate audience. First steps focused on building a storyboard, which is a visual outline of scenes to be animated. Then we organized a team of geo scientists and animators to make the animation. Students generated a rough draft animation, which was polished by a professional animator. We also wrote a narrative that was keyed to the animation, with written "call outs" inserted when terms that may be unfamiliar to undergraduates were spoken. Concepts in the animation are explicitly linked to the scientific literature, with references intended to guide interested viewers to sources to learn more. After the animation and narration were completed, we focused on dissemina tion and assessment. The animation ("Plate Tectonics Basics 1") was placed on YouTube and the Science Education Resource Center (SERC) portal, and a Jap anese version was made. Presentations about the animation were given at the Geological Society of America (GSA) annual meeting and the American Geo physical Union (AGU) Fall meeting. Assessment focused on capturing student understandings before and after watching the animation. Three groups of stu dents were assessed: community college students and lower and upperlevel students at a fouryear university. Results of the assessment indicate that stu dents at all levels improved their understanding of subduction zone processes after experiencing the animation, but that upperlevel students showed the greatest improvement. More highquality animations about important plate tectonic processes and additional research into the level of complexity for var ious student groups are required.

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