Nathan Bridges Print


  240-228-5753

  Nathan.Bridges@jhuapl.edu

: SES

:   Planetary Geologist

:  Planetary

  Mars 2020, SuperCam, MEDA, MRO, HiRISE, MSL, ChemCam

 
Degree Field of Study Year Attained Institution Name
Ph.D. Geology 1997 University of Massachusetts
MS Geology 1992 Arizona State University
BA Geology 1989 University of Colorado

Nathan passed away April 26, 2017. This profile is static for legacy purposes.

I am a research scientist at the Johns Hopkins University Applied Physics Laboratory, where I have worked since 2009. Prior to that I was at the Jet Propulsion Laboratory (1997-2009). Currently I am also an Associate Research Professor in the Earth and Planetary Science Department at Johns Hopkins University. My primary research focus is planetary surface processes, in particular the mechanisms, rates, and dynamics of wind and associated particle transport on Mars, Earth, and Titan. In my work, I combine mission participation and data analysis, field investigations, experiments (mainly in wind tunnels), and modeling.  I'm a Co-Investigator on the HiRISE camera on the Mars Reconnaissance Orbiter, ChemCam on the Mars Science Laboratory/Curiosity rover, and the Mars Environmental Dynamics Analyzer (MEDA) on the Mars-2020 rover. I'm also a Collaborator on SuperCam on Mars-2020, and PI on NASA grants to study sand dune motion on Mars and Titan.

 
AGU Index Category AGU Index Sub-Category
PLANETARY SCIENCES: SOLID SURFACE PLANETS Surface materials and properties
:
Start Year End Year Description
2009 Current Staff Scientist, Johns Hopkins University Applied Physics Laboratory
1997 2009 Research Scientist, Jet Propulsion Laboratory
Start Year End Year Description
1988 Current American Geophysical Union member
1997 Current Geological Society of America member
2011 2013 Eos Editorial Advisory Board (Planetary Section)
2013 2014 AGU Planetary Section Secretary
2015 Current AGU Planetary Section President-Elect
2015 2015 Mars Next Orbiter Science Advisory Group
Year Description
1992 Dwornik Best Student Paper Award at Lunar and Planetary Science Conference
2005 NASA Group Achievement Award, MER Science/Science Support Team
2006 NASA Group Achievement Award, MRO Project Development Team
2011 NASA Group Achievement Award, MRO HiRISE Science Team
2013 NASA Group Achievement Award, MSL ChemCam Instrument Develop. and Science Team
2015 NASA Group Achievement Award, MSL Prime Mission Science and Operations Team
:
The following publication information was downloaded from http://www.researcherId.com/rid/D-6341-2016.
Zimbelman, J. R., Scheidt, S. P., de Silva, S. L., Bridges, N. T., Spagnuolo, M. G., Neely, E. M., (2016), Aerodynamic roughness height for gravel-mantled megaripples, with implications for wind profiles near TARs on Mars, Icarus, 266, 306-314

Bridges, N. T., Spagnuolo, M. G., de Silva, S. L., Zimbelman, J. R., Neely, E. M., (2015), Formation of gravel-mantled megaripples on Earth and Mars: Insights from the Argentinean Puna and wind tunnel experiments, Aeolian Research, 17, 49-60

Bridges, Nathan T., Tamppari, Leslie K., (2015), Dynamic Mars from long-term observations: Introduction, Icarus, 251, 1-4

Burr, Devon M., Bridges, Nathan T., Marshall, John R., Smith, James K., White, Bruce R., Emery, Joshua P., (2015), Higher-than-predicted saltation threshold wind speeds on Titan, Nature, 517, 60-U137

Burr, Devon M., Bridges, Nathan T., Smith, James K., Marshall, John R., White, Bruce R., Williams, David A., (2015), The Titan Wind Tunnel: A new tool for investigating extraterrestrial aeolian environments, Aeolian Research, 18, 205-214

Le Mouelic, S., Gasnault, O., Herkenhoff, K. E., Bridges, N. T., Langevin, Y., Mangold, N., Maurice, S., Wiens, R. C., Pinet, P., Newsom, H. E., Deen, R. G., Bell, J. F., III, Johnson, J. R., Rapin, W., Barraclough, B., Blaney, D. L., Deflores, L., Maki, J., Malin, M. C., Perez, R., Saccoccio, M., (2015), The ChemCam Remote Micro-Imager at Gale crater: Review of the first year of operations on Mars, Icarus, 249, 93-107

Newsom, Horton E., Mangold, Nicolas, Kah, Linda C., Williams, Joshua M., Arvidson, Ray E., Stein, Nathan, Ollila, Ann M., Bridges, John C., Schwenzer, Susanne P., King, Penelope L., Grant, John A., Pinet, Patrick, Bridges, Nathan T., Calef, Fred, III, Wiens, Roger C., Spray, John G., Vaniman, David T., Elston, Wolf E., Berger, Jeff A., Garvin, James B., Palucis, Marisa C., MSL Sci Team, (2015), Gale crater and impact processes - Curiosity's first 364 Sols on Mars, Icarus, 249, 108-128

Ayoub, F., Avouac, J. -P., Newman, C. E., Richardson, M. I., Lucas, A., Leprince, S., Bridges, N. T., (2014), Threshold for sand mobility on Mars calibrated from seasonal variations of sand flux, Nature Communications, 5

Bridges, N. T., Calef, F. J., Hallet, B., Herkenhoff, K. E., Lanza, N. L., Le Mouelic, S., Newman, C. E., Blaney, D. L., de Pablo, M. A., Kocurek, G. A., Langevin, Y., Lewis, K. W., Mangold, N., Maurice, S., Meslin, P. -Y., Pinet, P., Renno, N. O., Rice, M. S., Richardson, M. E., Sautter, V., Sletten, R. S., Wiens, R. C., Yingst, R. A., (2014), The rock abrasion record at Gale Crater: Mars Science Laboratory results from Bradbury Landing to Rocknest, Journal of Geophysical Research-Planets, 119, 1374-1389

Lorenz, Ralph D., Bridges, Nathan T., Rosenthal, Alex A., Donkor, Elise, (2014), Elevation dependence of bedform wavelength on Tharsis Montes, Mars: Atmospheric density as a controlling parameter, Icarus, 230, 77-80

Thomson, B. J., Hurowitz, J. A., Baker, L. L., Bridges, N. T., Lennon, A. M., Paulsen, G., Zacny, K., (2014), The effects of weathering on the strength and chemistry of Columbia River Basalts and their implications for Mars Exploration Rover Rock Abrasion Tool (RAT) results, Earth and Planetary Science Letters, 400, 130-144

de Silva, S. L., Spagnuolo, M. G., Bridges, N. T., Zimbelman, J. R., (2013), Gravel-mantled megaripples of the Argentinean Puna: A model for their origin and growth with implications for Mars, Geological Society of America Bulletin, 125, 1912-1929

Geissler, Paul E., Stantzos, Nicholas W., Bridges, Nathan T., Bourke, Mary C., Silvestro, Simone, Fenton, Lori K., (2013), Shifting sands on Mars: insights from tropical intra-crater dunes, Earth Surface Processes and Landforms, 38, 407-412

Thomson, B. J., Bridges, N. T., Cohen, J., Hurowitz, J. A., Lennon, A., Paulsen, G., Zacny, K., (2013), Estimating rock compressive strength from Rock Abrasion Tool (RAT) grinds, Journal of Geophysical Research-Planets, 118, 1233-1244

Bridges, N. T., Ayoub, F., Avouac, J-P., Leprince, S., Lucas, A., Mattson, S., (2012), Earth-like sand fluxes on Mars, Nature, 485, 339-342

Bridges, Nathan T., Bourke, Mary C., Geissler, Paul E., Banks, Maria E., Colon, Cindy, Diniega, Serina, Golombek, Matthew P., Hansen, Candice J., Mattson, Sarah, McEwen, Alfred S., Mellon, Michael T., Stantzos, Nicholas, Thomson, Bradley J., (2012), Planet-wide sand motion on Mars, Geology, 40, 31-34

Bridges, Nathan T., Muhs, Daniel R., Grotzinger, JP, Milliken, RE, (2012), DUSTSTONES ON MARS: SOURCE, TRANSPORT, DEPOSITION, AND EROSION, Sedimentary Geology of Mars, 102, 169-182

Hansen, C. J., Bourke, M., Bridges, N. T., Byrne, S., Colon, C., Diniega, S., Dundas, C., Herkenhoff, K., McEwen, A., Mellon, M., Portyankina, G., Thomas, N., (2011), Seasonal Erosion and Restoration of Mars' Northern Polar Dunes, Science, 331, 575-578

Thomas, N., Stelter, R., Ivanov, A., Bridges, N. T., Herkenhoff, K. E., McEwen, A. S., (2011), Spectral heterogeneity on Phobos and Deimos: HiRISE observations and comparisons to Mars Pathfinder results, Planetary and Space Science, 59, 1281-1292

Thomson, B. J., Bridges, N. T., Milliken, R., Baldridge, A., Hook, S. J., Crowley, J. K., Marion, G. M., de Souza Filho, C. R., Brown, A. J., Weitz, C. M., (2011), Constraints on the origin and evolution of the layered mound in Gale Crater, Mars using Mars Reconnaissance Orbiter data, Icarus, 214, 413-432

Bridges, N. T., Banks, M. E., Beyer, R. A., Chuang, F. C., Dobrea, E. Z. Noe, Herkenhoff, K. E., Keszthelyi, L. P., Fishbaugh, K. E., McEwen, A. S., Michaels, T. I., Thomson, B. J., Wray, J. J., (2010), Aeolian bedforms, yardangs, and indurated surfaces in the Tharsis Montes as seen by the HiRISE Camera: Evidence for dust aggregates, Icarus, 205, 165-182

Bridges, Nathan T., Razdan, Anshuman, Yin, Xuetao, Greeley, Ronald, Ali, Saif, Kushunapally, Rakesh, (2010), Quantification of shape and texture for wind abrasion studies: Proof of concept using analog targets, Geomorphology, 114, 213-226

Brown, Adrian J., Hook, Simon J., Baldridge, Alice M., Crowley, James K., Bridges, Nathan T., Thomson, Bradley J., Marion, Giles M., de Souza Filho, Carlos R., Bishop, Janice L., (2010), Hydrothermal formation of Clay-Carbonate alteration assemblages in the Nil Fossae region of Mars, Earth and Planetary Science Letters, 297, 174-182

Chuang, Frank C., Beyer, Ross A., Bridges, Nathan T., (2010), Modification of Martian slope streaks by eolian processes, Icarus, 205, 154-164

Delamere, W. Alan, Tornabene, Livio L., McEwen, Alfred S., Becker, Kris, Bergstrom, James W., Bridges, Nathan T., Eliason, Eric M., Gallagher, Dennis, Herkenhoff, Kenneth E., Keszthelyi, Laszlo, Mattson, Sarah, McArthur, Guy K., Mellon, Michael T., Milazzo, Moses, Russell, Patrick S., Thomas, Nicolas, (2010), Color imaging of Mars by the High Resolution Imaging Science Experiment (HiRISE), Icarus, 205, 38-52

Diniega, Serina, Byrne, Shane, Bridges, Nathan T., Dundas, Colin M., McEwen, Alfred S., (2010), Seasonality of present-day Martian dune-gully activity, Geology, 38, 1047-1050

McEwen, Alfred S., Banks, Maria E., Baugh, Nicole, Becker, Kris, Boyd, Aaron, Bergstrom, James W., Beyer, Ross A., Bortolini, Edward, Bridges, Nathan T., Byrne, Shane, Castalia, Bradford, Chuang, Frank C., Crumpler, Larry S., Daubar, Ingrid, Davatzes, Alix K., Deardorff, Donald G., DeJong, Alaina, Delamere, W. Alan, Dobrea, Eldar Noe, Dundas, Colin M., Eliason, Eric M., Espinoza, Yisrael, Fennema, Audrie, Fishbaugh, Kathryn E., Forrester, Terry, Geissler, Paul E., Grant, John A., Griffes, Jennifer L., Grotzinger, John P., Gulick, Virginia C., Hansen, Candice J., Herkenhoff, Kenneth E., Heyd, Rodney, Jaeger, Windy L., Jones, Dean, Kanefsky, Bob, Keszthelyi, Laszlo, King, Robert, Kirk, Randolph L., Kolb, Kelly J., Lasco, Jeffrey, Lefort, Alexandra, Leis, Richard, Lewis, Kevin W., Martinez-Alonso, Sara, Mattson, Sarah, McArthur, Guy, Mellon, Michael T., Metz, Joannah M., Milazzo, Moses P., Milliken, Ralph E., Motazedian, Tahirih, Okubo, Chris H., Ortiz, Albert, Philippoff, Andrea J., Plassmann, Joseph, Polit, Anjani, Russell, Patrick S., Schaller, Christian, Searls, Mindi L., Spriggs, Timothy, Squyres, Steven W., Tarr, Steven, Thomas, Nicolas, Thomson, Bradley J., Tornabene, Livio L., Van Houten, Charlie, Verba, Circe, Weitz, Catherine M., Wray, James J., (2010), The High Resolution Imaging Science Experiment (HiRISE) during MRO's Primary Science Phase (PSP), Icarus, 205, 2-37

Silvestro, S., Fenton, L. K., Vaz, D. A., Bridges, N. T., Ori, G. G., (2010), Ripple migration and dune activity on Mars: Evidence for dynamic wind processes, Geophysical Research Letters, 37

Baldridge, A. M., Hook, S. J., Crowley, J. K., Marion, G. M., Kargel, J. S., Michalski, J. L., Thomson, B. J., de Souza Filho, C. R., Bridges, N. T., Brown, A. J., (2009), Contemporaneous deposition of phyllosilicates and sulfates: Using Australian acidic saline lake deposits to describe geochemical variability on Mars, Geophysical Research Letters, 36

Laity, Julie E., Bridges, Nathan T., (2009), Ventifacts on Earth and Mars: Analytical, field, and laboratory studies supporting sand abrasion and windward feature development, Geomorphology, 105, 202-217

Marion, G. M., Crowley, J. K., Thomson, B. J., Kargel, J. S., Bridges, N. T., Hook, S. J., Baldridge, A., Brown, A. J., da Luz, B. Ribeiro, de Souza Filho, C. R., (2009), Modeling aluminum-silicon chemistries and application to Australian acidic playa lakes as analogues for Mars, Geochimica Et Cosmochimica Acta, 73, 3493-3511

Greeley, Ronald, Whelley, Patrick L., Neakrase, Lynn D. V., Arvidson, Raymond E., Bridges, Nathan T., Cabrol, Nathalie A., Christensen, Philip R., Di, Kaichang, Foley, Daniel J., Golombek, Matthew P., Herkenhoff, Kenneth, Knudson, Amy, Kuzmin, Ruslan O., Li, Ron, Michaels, Timothy, Squyres, Steven W., Sullivan, Robert, Thompson, Shane D., (2008), Columbia Hills, Mars: Aeolian features seen from the ground and orbit, Journal of Geophysical Research-Planets, 113

Thomson, B. J., Bridges, N. T., Greeley, R., (2008), Rock abrasion features in the Columbia Hills, Mars, Journal of Geophysical Research-Planets, 113

Bridges, N. T., Geissler, P. E., McEwen, A. S., Thomson, B. J., Chuang, F. C., Herkenhoff, K. E., Keszthelyi, L. P., Martinez-Alonso, S., (2007), Windy Mars: A dynamic planet as seen by the HiRISE camera, Geophysical Research Letters, 34

Hudson, Troy L., Aharonson, Oded, Schorghofer, Norbert, Farmer, Crofton B., Hecht, Michael H., Bridges, Nathan T., (2007), Water vapor diffusion in Mars subsurface environments, Journal of Geophysical Research-Planets, 112

McEwen, A. S., Hansen, C. J., Delamere, W. A., Eliason, E. M., Herkenhoff, K. E., Keszthelyi, L., Gulick, V. C., Kirk, R. L., Mellon, M. T., Grant, J. A., Thomas, N., Weitz, C. M., Squyres, S. W., Bridges, N. T., Murchie, S. L., Seelos, F., Seelos, K., Okubo, C. H., Milazzo, M. P., Tornabene, L. L., Jaeger, W. L., Byrne, S., Russell, P. S., Griffes, J. L., Martinez-Alonso, S., Davatzes, A., Chuang, F. C., Thomson, B. J., Fishbaugh, K. E., Dundas, C. M., Kolb, K. J., Banks, M. E., Wray, J. J., (2007), A closer look at water-related geologic activity on Mars, Science, 317, 1706-1709

McEwen, Alfred S., Eliason, Eric M., Bergstrom, James W., Bridges, Nathan T., Hansen, Candice J., Delamere, W. Alan, Grant, John A., Gulick, Virginia C., Herkenhoff, Kenneth E., Keszthelyi, Laszlo, Kirk, Randolph L., Mellon, Michael T., Squyres, Steven W., Thomas, Nicolas, Weitz, Catherine M., (2007), Mars Reconnaissance Orbiter's High Resolution Imaging Science Experiment (HiRISE), Journal of Geophysical Research-Planets, 112

Bridges, Nathan T., Lackner, Claire N., (2006), Northern hemisphere Martian gullies and mantled terrain: Implications for near-surface water migration in Mars' recent past, Journal of Geophysical Research-Planets, 111

Bridges, NT, Phoreman, J, White, BR, Greeley, R, Eddlemon, EE, Wilson, GR, Meyer, CJ, (2005), Trajectories and energy transfer of saltating particles onto rock surfaces: Application to abrasion and ventifact formation on Earth and Mars, Journal of Geophysical Research-Planets, 110

Bridges, NT, Laity, JE, Greeley, R, Phoreman, J, Eddlemon, EE, (2004), Insights on rock abrasion and ventifact formation from laboratory and field analog studies with applications to Mars, Planetary and Space Science, 52, 199-213

Anderson, FS, Haldemann, AFC, Bridges, NT, Golombek, MP, Parker, TJ, Neumann, G, (2003), Analysis of MOLA data for the Mars Exploration Rover landing sites, Journal of Geophysical Research-Planets, 108

Golombek, MP, Grant, JA, Parker, TJ, Kass, DM, Crisp, JA, Squyres, SW, Haldemann, AFC, Adler, M, Lee, WJ, Bridges, NT, Arvidson, RE, Carr, MH, Kirk, RL, Knocke, PC, Roncoli, RB, Weitz, CM, Schofield, JT, Zurek, RW, Christensen, PR, Fergason, RL, Anderson, FS, Rice, JW, (2003), Selection of the Mars Exploration Rover landing sites, Journal of Geophysical Research-Planets, 108

Martin, TZ, Bridges, NT, Murphy, JR, (2003), Near-surface temperatures at proposed Mars Exploration Rover landing sites, Journal of Geophysical Research-Planets, 108

Bridges, NT, Herkenhoff, KE, (2002), Topography and geologic characteristics of aeolian grooves in the south polar layered deposits of Mars, Icarus, 156, 387-398

Greeley, R, Bridges, NT, Kuzmin, RO, Laity, JE, (2002), Terrestrial analogs to wind-related features at the Viking and Pathfinder landing sites on Mars, Journal of Geophysical Research-Planets, 107

Bridges, NT, Crisp, JA, Bell, JF, (2001), Characteristics of the Pathfinder APXS sites: Implications for the composition of Martian rocks and soils, Journal of Geophysical Research-Planets, 106, 14621-14665

Bell, JF, McSween, HY, Crisp, JA, Morris, RV, Murchie, SL, Bridges, NT, Johnson, JR, Britt, DT, Golombek, MP, Moore, HJ, Ghosh, A, Bishop, JL, Anderson, RC, Bruckner, J, Economou, T, Greenwood, JP, Gunnlaugsson, HP, Hargraves, RM, Hviid, S, Knudsen, JM, Madsen, MB, Reid, R, Rieder, R, Soderblom, L, (2000), Mineralogic and compositional properties of Martian soil and dust: Results from Mars Pathfinder, Journal of Geophysical Research-Planets, 105, 1721-1755

Golombek, MP, Bridges, NT, (2000), Erosion rates on Mars and implications for climate change: Constraints from the Pathfinder landing site, Journal of Geophysical Research-Planets, 105, 1841-1853

Greeley, R, Kraft, MD, Kuzmin, RO, Bridges, NT, (2000), Mars Pathfinder landing site: Evidence for a change in wind regime from lander and orbiter data, Journal of Geophysical Research-Planets, 105, 1829-1840

Vasavada, AR, Williams, JP, Paige, DA, Herkenhoff, KE, Bridges, NT, Greeley, R, Murray, BC, Bass, DS, McBride, KS, (2000), Surface properties of Mars' polar layered deposits and polar landing sites, Journal of Geophysical Research-Planets, 105, 6961-6969

Bridges, NT, Greeley, R, Haldemann, AFC, Herkenhoff, KE, Kraft, M, Parker, TJ, Ward, AW, (1999), Ventifacts at the Pathfinder landing site, Journal of Geophysical Research-Planets, 104, 8595-8615

Golombek, MP, Anderson, RC, Barnes, JR, Bell, JF, Bridges, NT, Britt, DT, Bruckner, J, Cook, RA, Crisp, D, Crisp, JA, Economou, T, Folkner, WM, Greeley, R, Haberle, RM, Hargraves, RB, Harris, JA, Haldemann, AFC, Herkenhoff, KE, Hviid, SF, Jaumann, R, Johnson, JR, Kallemeyn, PH, Keller, HU, Kirk, RL, Knudsen, JM, Larsen, S, Lemmon, MT, Madsen, MB, Magalhaes, JA, Maki, JN, Malin, MC, Manning, RM, Matijevic, J, McSween, HY, Moore, HJ, Murchie, SL, Murphy, JR, Parker, TJ, Rieder, R, Rivellini, TP, Schofield, JT, Seiff, A, Singer, RB, Smith, PH, Soderblom, LA, Spencer, DA, Stoker, CR, Sullivan, R, Thomas, N, Thurman, SW, Tomasko, MG, Vaughan, RM, Wanke, H, Ward, AW, Wilson, GR, (1999), Overview of the Mars Pathfinder Mission: Launch through landing, surface operations, data sets, and science results, Journal of Geophysical Research-Planets, 104, 8523-8553

Johnson, JR, Kirk, R, Soderblom, LA, Gaddis, L, Reid, RJ, Britt, DT, Smith, P, Lemmon, M, Thomas, N, Bell, JF, Bridges, NT, Anderson, R, Herkenhoff, KE, Maki, J, Murchie, S, Dummel, A, Jaumann, R, Trauthan, F, Arnold, G, (1999), Preliminary results on photometric properties of materials at the Sagan Memorial Station, Mars, Journal of Geophysical Research-Planets, 104, 8809-8830

McSween, HY, Murchie, SL, Crisp, JA, Bridges, NT, Anderson, RC, Bell, JF, Britt, DT, Bruckner, J, Dreibus, G, Economou, T, Ghosh, A, Golombek, MP, Greenwood, JP, Johnson, JR, Moore, HJ, Morris, RV, Parker, TJ, Rieder, R, Singer, R, Wanke, H, (1999), Chemical, multispectral, and textural constraints on the composition and origin of rocks at the Mars Pathfinder landing site, Journal of Geophysical Research-Planets, 104, 8679-8715

Bridges, NT, (1997), Ambient effects on basalt and rhyolite lavas under Venusian, subaerial, and subaqueous conditions, Journal of Geophysical Research-Planets, 102, 9243-9255

Bridges, NT, (1997), Characteristics of seamounts near Hawaii as viewed by GLORIA, Marine Geology, 138, 273-301

Smith, PH, Bell, JF, Bridges, NT, Britt, DT, Gaddis, L, Greeley, R, Keller, HU, Herkenhoff, KE, Jaumann, R, Johnson, JR, Kirk, RL, Lemmon, M, Maki, JN, Malin, MC, Murchie, SL, Oberst, J, Parker, TJ, Reid, RJ, Sablotny, R, Soderblom, LA, Stoker, C, Sullivan, R, Thomas, N, Tomasko, MG, Ward, W, Wegryn, E, (1997), Results from the Mars Pathfinder camera, Science, 278, 1758-1765

BRIDGES, NT, (1995), SUBMARINE ANALOGS TO VENUSIAN PANCAKE DOMES, Geophysical Research Letters, 22, 2781-2784

FINK, JH, BRIDGES, NT, (1995), EFFECTS OF ERUPTION HISTORY AND COOLING RATE ON LAVA DOME GROWTH, Bulletin of Volcanology, 57, 229-239

BRIDGES, NT, (1994), ELEVATION-CORRECTED THERMAL INERTIA AND DERIVED PARTICLE-SIZE ON MARS AND IMPLICATIONS FOR THE THARSIS-MONTES, Geophysical Research Letters, 21, 785-788

FINK, JH, BRIDGES, NT, GRIMM, RE, (1993), SHAPES OF VENUSIAN PANCAKE DOMES IMPLY EPISODIC EMPLACEMENT AND SILICIC COMPOSITION, Geophysical Research Letters, 20, 261-264