Research Interests


My research interests are in the areas of surficial geology and low-temperature mineralogy/geochemistry, especially as applied to tropical soils and fractured rock aquifers. Research methods include field work, XRD, SEM-EDS, XRF, ICPMS, TEM, FTIR and other complementary methods of major and trace element analysis. I also wrote a textboox (Environmental and Low-Temperature Geochemistry) that was published in 2014 by Wiley with a 2nd edition in 2019. An errata sheet for the 1st edition is availabe here pdf


Research Papers (* = student co-author)


  • Ryan, P.C., Alvarado, G.E., McCanta, M., Barca, M*, Davis, G*., 2022. The importance of overbank deposits and paleosol analyses for comprehensive volcanic hazard evaluation: the case of Holocene volcanism at Miravalles Volcano, Costa Rica. Nat Hazards 112, 413–449.

  • Munroe JS, Ryan PC, Proctor A*, 2021. Pedogenic clay formation from allochthonous parent materials in a periglacial alpine critical zone. Catena 203, 105324.

  • Munroe, J.S., Norris, E.D.*, Olson, P.M.*, Ryan, P.C., Tappa, M.J., Beard, B.L., 2020. Quantifying the contribution of dust to alpine soils in the periglacial zone of the Uinta Mountains, Utah, USA. Geoderma 378, 114631.

  • Ryan, P.C., Huertas, F.J., Pincus, L.N.*, Painter, W.*, 2020. Arsenic-bearing serpentine group minerals: Mineral synthesis with insights for the arsenic cycle. Clays and Clay Minerals 67, 488-506. DOI: 10.1007/s42860-019-00040-1.

  • Armfield, J., Perdrial, J., Gagnon, A., Ehrenkranz, J., Perdrial, N., Cincotta, M., Ross, D., Shanley, J., Underwood, K., Ryan, P.C., 2018. Does stream water composition at Sleepers River in Vermont reflect dynamic changes in soils during recovery from acidification? Frontiers in Earth Science 6: 246. doi: 10.3389/feart.2018.00246.

  • Van Hoesen, J., Arriaza, B., Ryan, P.C., Grady, C.M.*, 2018. A multi-analytical approach for identifying a manganese source for the black pigment of the Chinchorro mortuary palette. Geoarcheology DOI:10.1002/gea.21713.

  • Pincus, L.N.*, Ryan, P.C., Huertas, F.J., Alvarado, G.E., 2017. The influence of soil age and regional climate on clay mineralogy and cation exchange capacity of moist tropical soils: A case study from Late Quaternary chronosequences in Costa Rica. Geoderma 308, 130-148.

  • Ryan, P.C., Huertas, F.J., Hobbs, F.C.*, Pincus, L.N.*, 2016. Kaolinite and halloysite derived from sequential transformation of pedogenic smectite and kaolinite-smectite in a 120 ka tropical soil chronosequence. Clays and Clay Minerals, 64, 488–516.

  • Kim J.J., Comstock J., Ryan P.C., Heindel C., Koenigsberger S.*, 2016. Denitrification and dilution along fracture flowpaths influence the recovery of a bedrock aquifer from nitrate contamination. Science of the Total Environment 569–570, 450–468.

  • Ryan, P.C., West, D.P., Hattori, K., Studwell, S.*, Allen, D., Kim, J., 2015. The influence of metamorphic grade on arsenic in metasedimentary bedrock aquifers: A case study from western New England, USA. Science of the Total Environment 505, 1320–1330. pdf

  • Kim, J., Ryan, P.C., Klepeis, K., Gleeson, T., North, K.*, Bean, J.*, Davis, L.*, Filoon, J.*, 2014. Ordovician thrust fault controls hydrogeology and geochemistry of a bedrock aquifer system in NW Vermont: northeastern Appalachian foreland. Geofluids 14, 266-290. DOI: 10.1111/gfl.12076. pdf

  • Ryan P.C., Huertas, F.J., 2013. Reaction pathways of clay minerals in tropical soils: insights from kaolinite-smectite synthesis experiments. Clays and Clay Minerals 61, 303-318. pdf

  • Ryan, P.C., Kim, J.J., Mango, H., Hattori, K., Thompson, A.*, 2013. Arsenic in a fractured slate aquifer system, New England (USA): Influence of bedrock geochemistry, groundwater flow paths, redox and ion exchange. Applied Geochemistry 39, 181-192. doi: pdf

  • Ryan P.C., Kim J, Wall A.J., Moen, J.C.*, Corenthal, L.G.*, Chow, D.R.*, Sullivan, C.M.*, Bright, K.*, 2011. Ultramafic-derived arsenic in a fractured bedrock aquifer. Applied Geochemistry 26, 444-457. pdf

  • Ryan P.C., Huertas, F.J., 2009. The temporal evolution of pedogenic Fe-smectite to Fe-kaolin via interstratified kaolin-smectite in a moist tropical soil chronosequence. Geoderma 151, 1-15. pdf

  • Ryan P.C., Hillier S., Wall A.J.*, 2008, Stepwise effects of the BCR sequential chemical extraction procedure on dissolution and metal release from common ferromagnesian clay minerals: a combined solution chemistry and X-ray powder diffraction study. Science of the Total Environment 407, 603-614. pdf

  • Munroe J.S., Ryan P.C., Carlson H.A.*, and Miller E.K., 2008, Testing Latest Wisconsinan Ice Flow Directions in Vermont through Quantitative X-ray Diffraction Analysis of Soil Mineralogy. Northeastern Geology and Environmental Sciences, 29(4): 263-275. pdf

  • Munroe JS, Farrugia G*, Ryan PC. 2007. Parent material and chemical weathering in alpine soils on Mount Mansfield, Vermont, USA. Catena 70(1), 39-48. pdf

  • Fisher GB*, Ryan PC. 2006. The smectite to disordered kaolinite transition in a tropical soil chronosequence, Pacific Coast, Costa Rica. Clays & Clay Minerals 54, 571-586. pdf
    Click here for topographic map of Esterillos Terraces sample sites.

  • Kautz CQ*, Ryan PC. 2003. The 10 Å to 7 Å halloysite transition in a tropical soil sequence, Costa Rica. Clays and Clay Minerals 51, 252-263. pdf

  • Sears JW, Ryan PC. 2003. Cenozoic evolution of the Montana Cordillera: evidence from paleovalleys. Cenozoic Systems of the Rocky Mountain Region (Raynolds RG, Flores RM, Eds.), SEPM Special Publication, Denver, CO. pdf

  • Ryan PC, Wall AJ*, Hillier S, Clark L. 2002. Insights into sequential chemical extraction from quantitative XRD: A study of trace metal partitioning in sediments related to frog malformities. Chemical Geology 184, 337-357. pdf

  • Ryan PC, Hillier S. 2002. Facies relationships of Fe-rich clays in the Sundance Formation. American Mineralogist 87, 1607-1615. pdf

  • Hillier S, Ryan PC. 2002. Identification of halloysite (7Å) by ethylene glycol solvation: The MacEwan effect. Clay Minerals 37, 395-404. pdf

  • Ryan PC, Conrad ME, Brown K*, Chamberlain CP, Reynolds, RC Jr. 1998. Oxygen isotopic compositions of serpentine/chlorite and illite/smectite in the Tuscaloosa Formation (US Gulf Coast): Implications for pore fluids and mineralogic reactions. Clays and Clay Minerals 46, 357-368. pdf

  • Ryan PC, Buckley SN. 1998. Sedimentation, stratabound Cu-Ag mineralization, and syndepositional tectonics in the Revett Formation, Flathead Indian Reservation, western Montana: in The Belt Supergroup, Proc. Belt Symposium III, Special Pub. 112, Mont. Bur. of Mines Geol., 278-289. pdf

  • Ryan PC, Reynolds RC, Jr. 1997. The chemical composition of serpentine/chlorite: SEM-EDX vs. XRD determinations, implications for mineralogic reactions, and the origin of anatase. Clays and Clay Minerals 45, 339-352. pdf

  • Ryan PC, Reynolds RC, Jr. 1996. The origin and diagenesis of grain-coating serpentine/chlorite in Tuscaloosa Formation sandstone, U.S. Gulf Coast. American Mineralogist 81, 213-225. pdf

  • Moe JA, Ryan PC, Elliott WC, Reynolds RC, Jr. 1996. Petrology, chemistry, and clay mineralogy of a K-bentonite in the Proterozoic Belt Supergroup of western Montana: Journal of Sedimentary Research 66, 95-99. pdf

  • Buckley SN, Sears JW, Ryan PC, and Lauer D. 1994. Base-metal and PGE mineralization, sedimentation and mafic magmatism related to rifting of the Middle Proterozoic Belt Supergroup, western Montana: Northwest Geology 23 (Metallogeny of the Belt-Purcell Basin), 13-18. pdf