Talking rocks on the San Juan River, as part of the course Environmental Sciences of the lower San Juan River


Michael Ort

School of Earth Sciences and Environmental Sustainability
PO Box 4099
Northern Arizona University
Flagstaff, AZ, 86011 USA
928-523-9363 phone
928-523-9220 fax

I am a professor within the SESES and teach both geology and environmental sciences courses.  My research, which is described in more detail below, focuses on volcanoes.  I am particularly interested in a) human adaptations to cinder cone eruptions, b) phreatomagmatic processes (explosive water/magma interactions), c) pyroclastic flows and eruptions, d) environmental effects of eruptions, including chemical cycling, and e) crustal ascent processes (mostly using petrology and geochemistry as tools).



I teach courses in both Environmental Sciences and Geology.

Environmental Sciences: Generally, I teach ENV 385, Energy, Resources, and Policy in the spring, and ENV 360, Chemistry and Physics of the Environment in the fall semester.  Over the years, I have taught most of the environmental sciences courses at least once.  I created the course Environmental Sciences of the San Juan River (ENV 375) a few years ago and continue to be involved in it. 

Geology: In Geology, I teach undergraduate courses in Physical Geology (GLG 101), Field Mapping (GLG 240 and 440), and Igneous and Metamorphic Petrology (GLG 315), as well as graduate courses in Volcanology and Igneous Petrology (GLG 520 and 612).

2002 ENV 385 Resources and Policy class at Black Mesa Mine, Navajo Nation. Photo courtesy of Dave Ostergren.


1996 Graduate Volcanology class looking at maar deposits in the San Francisco volcanic field. Photo courtesy of Todd Keay.


Class Home Pages

My students have access to the class home page on NAU’s Vista site.



My research interests are diverse, but center on volcanoes.

I study volcanoes, with particular interest in the processes of pyroclastic currents and in magmatic processes in the crust. Typically, this involves careful fieldwork, paleomagnetism, and geochemistry.  My goals are to better understand explosive processes at volcanoes so that we can better protect the public from volcanic hazards.

I have several ongoing projects:

      Hopi Buttes (Tsezhin Bi'i) of NE Arizona: These are nephelinitic/monchiquitic (weirdo rocks!) volcanoes that formed maars, tuff rings, and tuff cones, as well as some spatter cones. The area was the site of a large playa in Miocene time, and the volcanoes erupted through saturated sediments. The exposures are fantastic, and my graduate students and I are investigating the phreatomagmatic eruption processes and sedimentary history of the area. Facies analysis allows us to determine how the pyroclastic currents changed character out from the vent, while vent facies analysis allows us to understand the processes of magma-water interaction better.  Anisotropy of magnetic susceptibility studies are helping us determine the depositional processes from the surges.  I would like to work with other students on processes of water-magma interactions, flow processes, and petrology at the Hopi Buttes.  Water-magma interactions are very common, but we do not understand why they occur in some eruptions but not in others, even at the same volcano.  We need to understand how magma and water interact explosively in order to be able to define hazards.  I am working with an MS student, Michaela Kim, from NAU and a PhD student, Giuseppe Re, from University of Otago on the Jagged Rocks dike complex to understand the magma feeder systems just beneath maar/diatremes.

      Mexico: I am working with Gerardo Carrasco-Núñez  on several Recent maar volcanoes in the Serdán-Oriental basin in the eastern part of the Central Volcanic Belt of Mexico.  We have been studying vent migrations at several maars, including Tecuitlapa and Atexcac.  My student, Allison Austin, studied a rhyolitic maar, Tepexitl, in great detail and then extended her study of rhyolite/water interaction processes while on a Fulbright scholarship in Germany.  She worked with Bernd Zimanowski carrying out explosion simulations using “magmas” from Tepexitl. 

      In the San Francisco volcanic field around Flagstaff, I am working with archaeologists and geomorphologists on a project studying the impact of the ~900 y.b.p. eruption of Sunset Crater on the people living here at that time.  This project has expanded to studying the interactions of humans and volcanoes at other very young scoria cones in southwestern North America, including Little Springs, Parcutin, and Jorullo.  Scoria cones are relatively small volcanoes that affect limited areas, but we have found that, because they commonly form where people are living, their effects on humans can be significant.  We have found evidence of human interactions with the eruptions themselves (offerings of corn and ceramic sherds), use of the lava flows for defensive purposes and caching water, as well as evidence of changes in agricultural practices in adaptation to the eruptions.  I have an NSF grant to study the eruption dynamics of Sunset Crater, a scoria cone that formed in a violent Strombolian eruption about 1085 CE.  One MS student, Karl Wagner, is currently working with me on this project.

      In addition, I have been working in the Campi Flegrei area of southern Italy for a number of years, studying the pyroclastic deposits associated with the ~40 ka Campanian Ignimbrite/Museo Breccia/Piperno Tuff eruption. Sandro De Vita and I are now working on resurgence dynamics in the caldera formed by the Monte Epomeo Green Tuff eruption about 55,000 years ago.  I also have a collaboration with Guido Giordano and Anna Paula Vinkler on the initiation of the Tufo Lionato eruption of the Colli Albani outside of Rome.  An NAU MS student, Sami Doupnik, is working on this project too. 

      Dendrochemical dating of eruptions: My colleagues, Paul Sheppard (dendrochronologist at University of Arizona) and Mark Elson (Desert Archaeology) and I have been developing a new way of dating young tephra-producing eruptions.  We are analyzing the chemical changes in tree rings caused by eruptions.  We are finding that trees take in different chemicals when their roots are covered by tephra, and we can detect this using the ICP-MS at NAU.  This technique appears to work well with cinder cones, and we are hoping to apply it to other types of volcanoes.  Currently, we are attempting to date the Sunset Crater eruption with this technique.  We are also using Sr isotopes to identify when a new Sr source arrived in the environment, and this seems to match well with the dendrochemical signal.

      Kathy Cashman, of University of Oregon, and I received NSF funding to study the 800 BP eruption of Quilotoa volcano in Ecuador.  We are working with Patty Mothes and Pete Hall of the Instituto Geofísico in Quito, Andrea di Muro of the Reunion Observatory, and Mauro Rosi of the Universitá di Pisa.  It produced two large ignimbrite-forming eruptions 800 years ago, with a several-week-long hiatus between them.  The second eruption began by producing a few surges and then an odd, very-crystal-rich fallout that is distributed for about 15 km radius around the vent.  How did this crystal fallout form, and what does it tell us about the eruption dynamics? 




Recent Publications

I can send pdfs of many of these papers upon request.  I also have several manuscripts submitted, so those may be available soon.


Ort, M.H., Di Muro, A., Michon, L., Bachèlery, P., in review, Explosive eruptions from the interaction of magmatic and hydrothermal systems during flank extension: The Bellecombe Ashes of Piton de La Fournaise (La Réunion Island), Bulletin of Volcanology, 25 ms pages.

Unema, J.A., Ort, M.H., Larsen, J.F., Neal, C.A. Schaefer, J.R., in review, Water-magma interaction and plume processes in the 2008 Okmok eruption, Geological Society of America Bulletin, 46 ms pages.

Soriano, C., Beamud, E., Garcés, M., Ort, M.H., in review, “Anomalous” magnetic fabrics of dikes in the superparamagnetic/single domain threshold, Geophysical Journal International, 53 ms pages.

Elson, M.D., Ort, M.H., Anderson, K.C., in press, Sunset Crater and Little Springs Volcano eruptions: 
Disaster management in the 11th century A.D. 
prehistoric Southwest; in How, Why, and Beyond: Exploring Cause and Explanation in Historical Ecology, Demography, and Movement, Herhahn, C., and Ramenofsky, A.F. (eds.). University of Colorado Press, Boulder.. 50 p text, four figures.

Elson, M.D., Ort, M.H., Sheppard, P.R., Samples, T.L., Anderson, K.C., and May, E.M., in press, A.D. 1064 No More? A multidisciplinary re-evaluation of the date of the eruption of Sunset Crater volcano, northern Arizona; University of Utah Press, 68 p. 7 figures, 3 tables.

Elson, M.D., Ort, M.H., and Heidke J.M., in press, Effects  of the ca. A.D. 1100  Sunset  Crater eruption on local populations, northern Arizona. In Proceedings of the 2002 Chacmool Conference, Calgary, Alberta. University of Calgary, Alberta, Canada, 20 manuscript pages.

Ort, M.H., Porreca, M. & Geissman, J.W., 2015, Introduction to The use of palaeomagnetism and rock magnetism to understand volcanic processes: in Ort, M.H., Porreca, M. & Geissman, J.W. (eds) The use of palaeomagnetism and rock magnetism to understand volcanic processes. Geological Society, London, Special Publications, 396, p. 1-11,

Ort, M.H., Newkirk, T.N., Vilas, J.F., Vazquez, J.A., 2015, Towards the definition of AMS facies in the deposits of pyroclastic density currents: in Ort, M.H., Porreca, M. & Geissman, J.W. (eds) The use of palaeomagnetism and rock magnetism to understand volcanic processes. Geological Society, London, Special Publications, 396, p. 205-226,

Ort, M.H., de Silva, S.L., Jiménez C., N., Jicha, B.R., Singer, B.S., 2013, Correlation of ignimbrites using characteristic remanent magnetism and anisotropy of magnetic susceptibility, central Andes, Bolivia; Geochemistry, Geophysics, Geosystems, v. 14, p. 141-157, doi: 10.1029/2012GC004276.

Elson, M.D., Ort, M.H., 2012, Fire in the sky: The eruption of Sunset Crater Volcano, in Downum, C., ed., Hisatsinom: Ancient peoples in a land without water. School for Advanced Research, Santa Fe, p. 26-33.

Elson, M.D., Ort, M,H., Anderson, K.C., Heidke, J.M., Sheppard, P.R., and Samples T.L., 2011, In the Shadow of the Volcano: Prehistoric Settlement in the U.S. 89 Project Area. In M.D. Elson (ed.) Sunset Crater Archaeology: The History of a Volcanic Landscape. Prehistoric Settlement in the Shadow of the Volcano, Anthropological Papers No. 37, Center for Desert Archaeology, Tucson, p. 187-211. 

Elson, M.D., Ort, M.H., Sheppard, P.R., Samples, T.L., Anderson, K.C., May, E.M., and Street, D.J., 2011, Sunset Crater Volcano. In M.D. Elson (ed.) Sunset Crater Archaeology: The History of a Volcanic Landscape. Prehistoric Settlement in the Shadow of the Volcano, Anthropological Papers No. 37, Center for Desert Archaeology, Tucson, p. 103-129.

Salisbury, M.J., Jicha, B.R., de Silva, S.L., Singer, B.S., Jiménez-C., N., Ort, M.H., 2011, 40Ar/39Ar chronostratigraphy of Altiplano-Puna Volcanic Complex ignimbrites reveals the development of a major silicic magmatic province; Geological Society of America Bulletin, v. 123, p. 821–840, doi: 10.1130/B30280.1.

Austin-Erickson, A., Ort, M.H., Carrasco-Núñez, G., 2011, Rhyolitic phreatomagmatism explored: Tepexitl Tuff Ring (Eastern Mexican Volcanic Belt), Journal of Volcanology and Geothermal Research, v. 201, p. 325-341.

Sheppard, P.R., Ort, M.H., Anderson, K,C., Clynne, M.A., May, E.M., 2009, Multiple dendrochronological responses to the eruption of Cinder Cone, Lassen Volcanic National Park, California, Dendrochronologia, v. 27, p. 213-221.    

Ort, M.H., Carrasco-Núñez, G., 2009, Lateral vent migration during phreatomagmatic and magmatic eruptions at Tecuitlapa Maar, east-central Mexico, Journal of Volcanology and Geothermal Research, v. 181, p. 67-77, doi:10.1016/j.jvolgeores.2009.01.003.

Sheppard, P.R., Ort, M.H., Anderson, K.C., Elson, M.D., Vázquez-Selem, L., Clemens, A.W., Little, N.C., and Speakman, R.J. 2008. Multiple dendrochronological signals indicate the eruption of Parícutin Volcano, Michoacán, Mexico. Tree-Ring Research 64(2):97-108.

Austin-Erickson, A., Büttner, R., Dellino, P., Ort, M. H., and Zimanowski, B., 2008, Phreatomagmatic explosions of rhyolitic magma: Experimental and field evidence, Journal of Geophysical Research, 113, B11201, doi:10.1029/2008JB005731.

Ort, M.H., Elson, M.D., Anderson, K.C., Duffield, W.A., and Samples, T.L., 2008, Variable Effects of Cinder-Cone Eruptions on Prehistoric Agrarian Human Populations in the American Southwest, Journal of Volcanology and Geothermal Research, v. 176, p. 363-376.

Pioli, L., Lanza, R., Ort, M.H., Rosi, M., 2008, Magnetic fabric, welding texture and strain fabric in the Nuraxi tuff, Sardinia, Italy, Bulletin of Volcanology, v. 70, p. 1123-1137.

Ort, M.H., Elson, M.D., Anderson, K.C., Duffield, W.A., Hooten, J.A., Champion, D.E., and Waring, G., 2008, Effects of Cinder Cone Eruptions upon Nearby Human Communities, Geological Society of America Bulletin, p. 476-486.

Elson, M. D., Ort, M.H., Anderson, K.A., and Heidke, J.M., 2007, Living with the volcano: the 11th century A.D. eruption of Sunset Crater. In Living under the shadow: Cultural impacts of volcanic eruptions: Walnut Creek, Left Coast Press, p. 107–132.

Carrasco-Núñez, G., Ort, M.H., and Romero, C., 2006, Anatomy of a maar volcano: Case study of Atexcac crater, eastern Mexico; Journal of Volcanology and Geothermal Research, v. 159, p. 179-197.

Vazquez, J.A., and Ort, M.H., 2006, Facies variation of eruption units produced by the passage of single pyroclastic surge currents, Hopi Buttes volcanic field, USA; Journal of Volcanology and Geothermal Research, 154:222–236.

Ort, M.H., Anderson, D.E., and Ostergren, D.M., 2006, Integrating Policy and Land Management Issues into a Natural Sciences Education: Teaching Environmental Sciences on the lower San Juan River, Utah, Journal of Geoscience Education, v. 53, p. 116-122.

Sheppard, P.R., May, E., Ort, M.H., Anderson, K., Elson, M.D., 2005, Dendrochronological responses to the 24 October 1992 tornado at Sunset Crater, northern Arizona; Canadian Journal of Forest Research, 35:2911-2919.

Dallegge, T.A., Ort, M.H., McIntosh, W.C., 2003, Mio-Pliocene chronostratigraphy, basin morphology and paleodrainage relations derived from the Bidahochi Formation, Hopi and Navajo Nations, northeastern Arizona: The Mountain Geologist, v. 40, no. 3, pp. 55-82.

Ort, M.H., Orsi, G., Pappalardo, L., and Fisher, R.V., 2003, Anisotropy of magnetic susceptibility studies of depositional processes in the Campanian Ignimbrite, Italy; Bulletin of Volcanology, 65:55-72.

Elson, M.D., Ort, M.H., Hesse, S. J., Duffield, W.A., 2002, Lava, corn, and ritual in the northern Southwest; American Antiquity, 67:119-135.

Hooten, J.A., Ort, M.H., 2002, Peperite as a Record of Early Stage Phreatomagmatic Fragmentation Processes: An Example from the Hopi Buttes Volcanic Field, Navajo Nation, Arizona, USA, Journal of Volcanology and Geothermal Research, 114:95-106.

Ort, MH, Elson, MD, and Champion, DE, 2002, A paleomagnetic dating study of Sunset Crater Volcano; Desert Archaeology, Inc. Technical Report No. 2002-16, 16 p.




Paleomagnetism Laboratory
I have a spinner magnetometer and an AF demagnetizer, which my students and I use for standard paleomagnetic studies and secular variation studies of volcanic deposits, which is especially useful for dating young volcanic units.  Currently, we are dating some Holocene flows in the Southwestern USA using secular variation.  I also have an AGICO Kappabridge KLY-4 on long-term loan that we use for anisotropy of magnetic susceptibility studies.  I have a student studying the emplacement dynamics fo the Peach Springs Tuff using this technique and several undergraduate students have carried out theses using this instrument.

Other Laboratories
The department has a well-equipped particle-size analysis laboratory.  A scanning electron microscope allows us to study features of minerals and volcanic shards.  My students and I use it for grain shape analysis.  We have access to several ICP-MS instruments and the sample-preparation laboratories that go with them.

Some Related Pages

Several other professors do volcano-related work at NAU:

Nancy Riggs, Professor, is a volcanologist:

Jim Wittke, Supervisor, Microprobe Lab:
The SESES home page, where you can find information on the academic programs, is


Ort's Home
created by Michael Ort, michael.ort@nau.eduNOSPAM
Dept. of Geology and Center for Environmental Sciences and Education, Northern Arizona University, Flagstaff, AZ 86011 USA