Kaj Williams, Ph.D.
My expertise is in developing and applying mathematical and computational methods for understanding physical processes on planetary surfaces and atmospheres.
Science and Products
Planetary Defense
At the USGS Astrogeology Science Center we conduct research on Planetary Defense. Planetary Defense involves predicting potential impactors (asteroids, comets), and studying how to deflect or divert them, as well as the potential effects of an impact. Effects include short-term effects such as blast damage, but also long-term effects such as climate and social impacts.
Surface - Atmosphere interaction
The USGS Astrogeology Science Center conducts research on the interaction between planetary surfaces and the overlying atmospheres. In particular, the transfer of momentum (from wind), vapor (evaporation/sublimation), liquid (rainfall, percolation, infiltration) and solids (snow) occurs between surfaces and atmospheres.
Planetary Volatiles: Snow and Ice
The USGS Astrogeology Science Center conducts research on planetary volatiles. Volatiles include substances that have a high vapor pressure relative to the ambient atmosphere. We study the longevity, locations and other characteristics of volatiles. More specifically: H2O ice, snow and frost are volatiles on the Earth. We study the persistence of perennial snowfields in Colorado and Mongolia. Mars...
Caves
The USGS Astrogeology Science Center conducts research on caves. In particular, we are interested in the physics of caves, which involves the application of the principles of heat transfer, mass transfer and meteorology to understand how cave climates evolve. We are also interested in caves on other planetary bodies and moons, and how they may be used as resources for future missions.
Terrestrial Analogs for Research and Geologic Exploration Training (TARGET)
The U. S. Geological Survey (USGS) Astrogeology Science Center (ASC) recently established the Terrestrial Analogs for Research and Geologic Exploration Training (TARGET) program. This service-oriented program is built around the recognition that the Earth is a fundamental training ground for human and robotic planetary exploration, and that ASC is in a unique position in northern Arizona with...
Meteorological Data for Grand Falls Dune Field, Arizona from 2009-2014 (ver. 1.1, December 2025) Meteorological Data for Grand Falls Dune Field, Arizona from 2009-2014 (ver. 1.1, December 2025)
Grand Falls Dune Field (GFDF) on the Navajo Nation (70 km NE of Flagstaff, AZ) is an active, bimodal dune system in both grain size and composition. Felsic grains derive from the Little Colorado River, while mafic (basaltic) grains are sourced locally from nearby cinder cones, making GFDF an excellent terrestrial analog for dune fields on Mars, Venus, and Titan. A long‑term...
Imagery, sediment collection, photogrammetry, and meteorological data from July 2023 to November 2024, Grand Falls Dune Field, Arizona Imagery, sediment collection, photogrammetry, and meteorological data from July 2023 to November 2024, Grand Falls Dune Field, Arizona
Grand Falls dune field (GFDF) is located on the Navajo Nation, ~70 km NE of Flagstaff, AZ. This active dune field displays a range of morphologies, including barchans, dome dunes, smaller dunes, and ripples, and is bimodal both in mineralogical composition and grain size distribution. The felsic component is likely derived from the Little Colorado River, and the mafic component (basaltic...
Ice cave climate data and frost imagery at Sunset Crater, AZ: 02 March 2021 to 13 December 2022 Ice cave climate data and frost imagery at Sunset Crater, AZ: 02 March 2021 to 13 December 2022
The purpose of the data collection was to monitor the microclimate in the “Bonito Flow” Ice Cave located in Sunset Crater National Monument. This cave is considered a sacred spot for some southwestern tribes as it was a historical source for ice. The main purpose of the climate monitoring was to determine if the cave is still an active ice cave, i.e., a cave that contains perennial ice...
Imagery, sediment collection, photogrammetry, and meteorological data from April 2023 to July 2023, Grand Falls Dune Field, Arizona Imagery, sediment collection, photogrammetry, and meteorological data from April 2023 to July 2023, Grand Falls Dune Field, Arizona
Grand Falls dune field (GFDF) is located on the Navajo Nation, ~70 km NE of Flagstaff, AZ. This active dune field displays a range of morphologies, including barchans, smaller dunes, and ripples, and is bimodal in composition. The felsic component is likely derived from the Little Colorado River, and the mafic component (basaltic grains) is locally sourced from nearby cinder cones [1]...
Imagery, photogrammetry, and meteorological data from December 2022 to April 2023, Grand Falls Dune Field, Arizona Imagery, photogrammetry, and meteorological data from December 2022 to April 2023, Grand Falls Dune Field, Arizona
Our goal for this work is to place better constraints on aeolian atmospheric-surface interactions through long-term monitoring of an active, bi-modal dune field located near Grand Falls, Arizona. Grand Falls dune field (GFDF) is located on the Navajo Nation, ~70 km NE of Flagstaff, AZ. This dune field has been monitored since 2013 by the U.S. Geological Survey, and data from each...
Imagery, photogrammetry, and meteorological data from December 2021 to December 2022, Grand Falls Dune Field, Arizona Imagery, photogrammetry, and meteorological data from December 2021 to December 2022, Grand Falls Dune Field, Arizona
Grand Falls dune field (GFDF) is located on the Navajo Nation, ~70 km NE of Flagstaff, AZ. This active dune field displays a range of morphologies, including barchans, smaller dunes, and ripples, and is bimodal in composition. The felsic component is likely derived from the Little Colorado River, and the mafic component (basaltic grains) is locally sourced from nearby cinder cones [1]...
Filter Total Items: 18
Summer snow determines the depth to ice-cemented ground under dry permafrost in Antarctica Summer snow determines the depth to ice-cemented ground under dry permafrost in Antarctica
Dry permafrost underlain by ice-cemented permafrost has been reported in several locations in Antarctica. Initially thought to be relic ice, it is now understood that this subsurface ice is in equilibrium with the surface conditions, although it is not in equilibrium with the atmosphere. We use year-round data from University Valley in the Dry Valleys and Elephant Head in the Ellsworth...
Authors
C. P. McKay, M. Marinova, Kaj E. Williams, M. Mellon
Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars
This work presents geomorphological analyses of an area at the boundary between Arcadia Planitia and northern Amazonis Planitia, situated in the northern mid-latitudes of Mars. Recent studies have indicated the presence of substantial volumes of near-surface excess ice in Arcadia Planitia, making this region a promising candidate for future human and robotic exploration. This study...
Authors
Erica Luzzi, Jennifer L. Heldmann, Kaj E. Williams, Giacomo Nodjoumi, Ariel Deutsch, Alexander Sehlke
Late Amazonian ice near Athabasca Valles, Mars: Recent megaflood or climate change? Late Amazonian ice near Athabasca Valles, Mars: Recent megaflood or climate change?
The Athabasca Valles outflow channel system is among the youngest such channels on Mars, with the Athabasca Valles flood lava (AVFL) covering the channel floor and reaching far beyond. Volcanic rootless cones on the AVFL indicate the presence of H2O in the shallow subsurface at the time of lava emplacement. However, Athabasca Valles are near the equator, where ice would rapidly sublime...
Authors
Colin M. Dundas, Laszlo P. Keszthelyi, Kaj E. Williams
Cave climate 100 meters below the surface in the pseudokarst of the Kilauea Southwest Rift Zone, Hawaii Cave climate 100 meters below the surface in the pseudokarst of the Kilauea Southwest Rift Zone, Hawaii
Kīlauea volcano hosts numerous pit craters that are inferred to have formed in competent bedrock (lava flows with minor tephra and other sediments), including Wood Valley Pit Crater. The Wood Valley Pit Crater is a 50-meter-deep, nearly circular pit that includes access to a cave entrance, which provides an opportunity to monitor cave climate throughout a cave that is ordinarily...
Authors
Timothy N. Titus, Glen E. Cushing, Chris Okubo, Kaj E. Williams
It’s time for focused in situ studies of planetary surface-atmosphere interactions It’s time for focused in situ studies of planetary surface-atmosphere interactions
A critical gap in planetary observations has been in situ characterization of extra-terrestrial, present-day atmospheric and surface environments and activity. While some surface activity has been observed and some in situ meteorological measurements have been collected by auxiliary instruments on Mars, existing information is insufficient to conclusively characterize the natural...
Authors
Serina Diniega, Nathan Barba, Louis Giersch, Brian Jackson, Alejandro Soto, Don Banfield, Mackenzie D. Day, Gary Doran, Colin M. Dundas, Michael Mischna, Scot Rafkin, Isaac B. Smith, Rob Sullivan, Christy Swann, Timothy N. Titus, Ian J. Walker, Jacob Widmer, Devon M. Burr, Lukas Mandrake, Nathalie Vriend, Kaj E. Williams
The formation mechanisms for mid-latitude ice scarps on Mars The formation mechanisms for mid-latitude ice scarps on Mars
Mid-latitude exposed ice scarps have recently been identified on Mars (Dundas et al., 2018; 2021). The presence of such surface ice exposures at relatively low latitudes was itself a mystery, and the formation dynamics of such scarps have also not been explained. In this work we model the ice ablation rates of several identified mid-latitude scarps. We find that, given certain...
Authors
Kaj E. Williams, Colin M. Dundas, Melinda A. Kahre
Non-USGS Publications**
Williams, Kaj, Christopher P. McKay and J.L Heldmann. (2015) Modeling the effects of Martian surface frost on ice table depth. Icarus, 261, 58-65.
Williams, Kaj and Chris McKay. (2015). Comparing flow-through and static ice cave models for Shoshone Ice Cave. International Journal of Speleology, 44: 1.
Heldmann, J. L., W. Pollard, C. P. Mckay, M. M. Marinova, A. Davila, K. E. Williams, D. Lacelle, and D. T. Andersen (2013), The high elevation Dry Valleys in Antarctica as analog sites for subsurface ice on Mars, Planetary and Space Science, 85(C), doi:10.1016/j.pss.2013.05.019.
J.L. Heldmann, M. Marinova, K.E. Williams, D. Lacelle, C.P. McKay, A. Davila, W. Pollard and D.T. Andersen (2012). Formation and evolution of buried snowpack deposits in Pearse Valley, Antarctica, and implications for Mars. Antarctic Science, 24, doi:10.1017/S0954102011000903
Williams, K. E., McKay, C. P. and Persson, F. (2012) The surface energy balance at the Huygens Landing site and the moist surface conditions on Titan. Planetary and Space Science. Vol 60, nr. 1.
Williams, K. E., Pappalardo, R. T. (2011) Variability in the Small Crater Population of Callisto. Icarus 215,1.
Williams, K.E., McKay, C. P., Toon, O.B., Head, J. W. (2010) Do Ice Caves Exist on Mars? Icarus 209,2.
Williams, K.E., Toon, O. B., Heldmann, J. L., Mellon, M. (2009) Ancient melting of mid-latitude snowpacks on Mars as a water source for gullies, Icarus, 200.
Williams, K.E., Toon, O.B., Heldmann, J.L. , McKay C.P. and Mellon, M. (2008) Stability of Mid-Latitude Snowpacks on Mars, Icarus, 196.
Williams, K. E., O. B. Toon, and J. Heldmann (2007), Modeling water ice lifetimes at recent Martian gully locations, Geophys. Res. Lett., 34, L09204, doi:10.1029/2007GL029507.
Lai, Y.C., Lerner, D, Williams, K and Crebogi, C. (Nov. 1999) Unstable dimension variability in coupled chaotic systems. Physical Review E 60 (5): 5445-5454 : A.
**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.
Integrated Software for Imagers and Spectrometers Integrated Software for Imagers and Spectrometers
A software library and set of tools to support ingestion, processing, and analysis of planetary science data. Version 8.0.2
Science and Products
Planetary Defense
At the USGS Astrogeology Science Center we conduct research on Planetary Defense. Planetary Defense involves predicting potential impactors (asteroids, comets), and studying how to deflect or divert them, as well as the potential effects of an impact. Effects include short-term effects such as blast damage, but also long-term effects such as climate and social impacts.
Surface - Atmosphere interaction
The USGS Astrogeology Science Center conducts research on the interaction between planetary surfaces and the overlying atmospheres. In particular, the transfer of momentum (from wind), vapor (evaporation/sublimation), liquid (rainfall, percolation, infiltration) and solids (snow) occurs between surfaces and atmospheres.
Planetary Volatiles: Snow and Ice
The USGS Astrogeology Science Center conducts research on planetary volatiles. Volatiles include substances that have a high vapor pressure relative to the ambient atmosphere. We study the longevity, locations and other characteristics of volatiles. More specifically: H2O ice, snow and frost are volatiles on the Earth. We study the persistence of perennial snowfields in Colorado and Mongolia. Mars...
Caves
The USGS Astrogeology Science Center conducts research on caves. In particular, we are interested in the physics of caves, which involves the application of the principles of heat transfer, mass transfer and meteorology to understand how cave climates evolve. We are also interested in caves on other planetary bodies and moons, and how they may be used as resources for future missions.
Terrestrial Analogs for Research and Geologic Exploration Training (TARGET)
The U. S. Geological Survey (USGS) Astrogeology Science Center (ASC) recently established the Terrestrial Analogs for Research and Geologic Exploration Training (TARGET) program. This service-oriented program is built around the recognition that the Earth is a fundamental training ground for human and robotic planetary exploration, and that ASC is in a unique position in northern Arizona with...
Meteorological Data for Grand Falls Dune Field, Arizona from 2009-2014 (ver. 1.1, December 2025) Meteorological Data for Grand Falls Dune Field, Arizona from 2009-2014 (ver. 1.1, December 2025)
Grand Falls Dune Field (GFDF) on the Navajo Nation (70 km NE of Flagstaff, AZ) is an active, bimodal dune system in both grain size and composition. Felsic grains derive from the Little Colorado River, while mafic (basaltic) grains are sourced locally from nearby cinder cones, making GFDF an excellent terrestrial analog for dune fields on Mars, Venus, and Titan. A long‑term...
Imagery, sediment collection, photogrammetry, and meteorological data from July 2023 to November 2024, Grand Falls Dune Field, Arizona Imagery, sediment collection, photogrammetry, and meteorological data from July 2023 to November 2024, Grand Falls Dune Field, Arizona
Grand Falls dune field (GFDF) is located on the Navajo Nation, ~70 km NE of Flagstaff, AZ. This active dune field displays a range of morphologies, including barchans, dome dunes, smaller dunes, and ripples, and is bimodal both in mineralogical composition and grain size distribution. The felsic component is likely derived from the Little Colorado River, and the mafic component (basaltic...
Ice cave climate data and frost imagery at Sunset Crater, AZ: 02 March 2021 to 13 December 2022 Ice cave climate data and frost imagery at Sunset Crater, AZ: 02 March 2021 to 13 December 2022
The purpose of the data collection was to monitor the microclimate in the “Bonito Flow” Ice Cave located in Sunset Crater National Monument. This cave is considered a sacred spot for some southwestern tribes as it was a historical source for ice. The main purpose of the climate monitoring was to determine if the cave is still an active ice cave, i.e., a cave that contains perennial ice...
Imagery, sediment collection, photogrammetry, and meteorological data from April 2023 to July 2023, Grand Falls Dune Field, Arizona Imagery, sediment collection, photogrammetry, and meteorological data from April 2023 to July 2023, Grand Falls Dune Field, Arizona
Grand Falls dune field (GFDF) is located on the Navajo Nation, ~70 km NE of Flagstaff, AZ. This active dune field displays a range of morphologies, including barchans, smaller dunes, and ripples, and is bimodal in composition. The felsic component is likely derived from the Little Colorado River, and the mafic component (basaltic grains) is locally sourced from nearby cinder cones [1]...
Imagery, photogrammetry, and meteorological data from December 2022 to April 2023, Grand Falls Dune Field, Arizona Imagery, photogrammetry, and meteorological data from December 2022 to April 2023, Grand Falls Dune Field, Arizona
Our goal for this work is to place better constraints on aeolian atmospheric-surface interactions through long-term monitoring of an active, bi-modal dune field located near Grand Falls, Arizona. Grand Falls dune field (GFDF) is located on the Navajo Nation, ~70 km NE of Flagstaff, AZ. This dune field has been monitored since 2013 by the U.S. Geological Survey, and data from each...
Imagery, photogrammetry, and meteorological data from December 2021 to December 2022, Grand Falls Dune Field, Arizona Imagery, photogrammetry, and meteorological data from December 2021 to December 2022, Grand Falls Dune Field, Arizona
Grand Falls dune field (GFDF) is located on the Navajo Nation, ~70 km NE of Flagstaff, AZ. This active dune field displays a range of morphologies, including barchans, smaller dunes, and ripples, and is bimodal in composition. The felsic component is likely derived from the Little Colorado River, and the mafic component (basaltic grains) is locally sourced from nearby cinder cones [1]...
Filter Total Items: 18
Summer snow determines the depth to ice-cemented ground under dry permafrost in Antarctica Summer snow determines the depth to ice-cemented ground under dry permafrost in Antarctica
Dry permafrost underlain by ice-cemented permafrost has been reported in several locations in Antarctica. Initially thought to be relic ice, it is now understood that this subsurface ice is in equilibrium with the surface conditions, although it is not in equilibrium with the atmosphere. We use year-round data from University Valley in the Dry Valleys and Elephant Head in the Ellsworth...
Authors
C. P. McKay, M. Marinova, Kaj E. Williams, M. Mellon
Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars
This work presents geomorphological analyses of an area at the boundary between Arcadia Planitia and northern Amazonis Planitia, situated in the northern mid-latitudes of Mars. Recent studies have indicated the presence of substantial volumes of near-surface excess ice in Arcadia Planitia, making this region a promising candidate for future human and robotic exploration. This study...
Authors
Erica Luzzi, Jennifer L. Heldmann, Kaj E. Williams, Giacomo Nodjoumi, Ariel Deutsch, Alexander Sehlke
Late Amazonian ice near Athabasca Valles, Mars: Recent megaflood or climate change? Late Amazonian ice near Athabasca Valles, Mars: Recent megaflood or climate change?
The Athabasca Valles outflow channel system is among the youngest such channels on Mars, with the Athabasca Valles flood lava (AVFL) covering the channel floor and reaching far beyond. Volcanic rootless cones on the AVFL indicate the presence of H2O in the shallow subsurface at the time of lava emplacement. However, Athabasca Valles are near the equator, where ice would rapidly sublime...
Authors
Colin M. Dundas, Laszlo P. Keszthelyi, Kaj E. Williams
Cave climate 100 meters below the surface in the pseudokarst of the Kilauea Southwest Rift Zone, Hawaii Cave climate 100 meters below the surface in the pseudokarst of the Kilauea Southwest Rift Zone, Hawaii
Kīlauea volcano hosts numerous pit craters that are inferred to have formed in competent bedrock (lava flows with minor tephra and other sediments), including Wood Valley Pit Crater. The Wood Valley Pit Crater is a 50-meter-deep, nearly circular pit that includes access to a cave entrance, which provides an opportunity to monitor cave climate throughout a cave that is ordinarily...
Authors
Timothy N. Titus, Glen E. Cushing, Chris Okubo, Kaj E. Williams
It’s time for focused in situ studies of planetary surface-atmosphere interactions It’s time for focused in situ studies of planetary surface-atmosphere interactions
A critical gap in planetary observations has been in situ characterization of extra-terrestrial, present-day atmospheric and surface environments and activity. While some surface activity has been observed and some in situ meteorological measurements have been collected by auxiliary instruments on Mars, existing information is insufficient to conclusively characterize the natural...
Authors
Serina Diniega, Nathan Barba, Louis Giersch, Brian Jackson, Alejandro Soto, Don Banfield, Mackenzie D. Day, Gary Doran, Colin M. Dundas, Michael Mischna, Scot Rafkin, Isaac B. Smith, Rob Sullivan, Christy Swann, Timothy N. Titus, Ian J. Walker, Jacob Widmer, Devon M. Burr, Lukas Mandrake, Nathalie Vriend, Kaj E. Williams
The formation mechanisms for mid-latitude ice scarps on Mars The formation mechanisms for mid-latitude ice scarps on Mars
Mid-latitude exposed ice scarps have recently been identified on Mars (Dundas et al., 2018; 2021). The presence of such surface ice exposures at relatively low latitudes was itself a mystery, and the formation dynamics of such scarps have also not been explained. In this work we model the ice ablation rates of several identified mid-latitude scarps. We find that, given certain...
Authors
Kaj E. Williams, Colin M. Dundas, Melinda A. Kahre
Non-USGS Publications**
Williams, Kaj, Christopher P. McKay and J.L Heldmann. (2015) Modeling the effects of Martian surface frost on ice table depth. Icarus, 261, 58-65.
Williams, Kaj and Chris McKay. (2015). Comparing flow-through and static ice cave models for Shoshone Ice Cave. International Journal of Speleology, 44: 1.
Heldmann, J. L., W. Pollard, C. P. Mckay, M. M. Marinova, A. Davila, K. E. Williams, D. Lacelle, and D. T. Andersen (2013), The high elevation Dry Valleys in Antarctica as analog sites for subsurface ice on Mars, Planetary and Space Science, 85(C), doi:10.1016/j.pss.2013.05.019.
J.L. Heldmann, M. Marinova, K.E. Williams, D. Lacelle, C.P. McKay, A. Davila, W. Pollard and D.T. Andersen (2012). Formation and evolution of buried snowpack deposits in Pearse Valley, Antarctica, and implications for Mars. Antarctic Science, 24, doi:10.1017/S0954102011000903
Williams, K. E., McKay, C. P. and Persson, F. (2012) The surface energy balance at the Huygens Landing site and the moist surface conditions on Titan. Planetary and Space Science. Vol 60, nr. 1.
Williams, K. E., Pappalardo, R. T. (2011) Variability in the Small Crater Population of Callisto. Icarus 215,1.
Williams, K.E., McKay, C. P., Toon, O.B., Head, J. W. (2010) Do Ice Caves Exist on Mars? Icarus 209,2.
Williams, K.E., Toon, O. B., Heldmann, J. L., Mellon, M. (2009) Ancient melting of mid-latitude snowpacks on Mars as a water source for gullies, Icarus, 200.
Williams, K.E., Toon, O.B., Heldmann, J.L. , McKay C.P. and Mellon, M. (2008) Stability of Mid-Latitude Snowpacks on Mars, Icarus, 196.
Williams, K. E., O. B. Toon, and J. Heldmann (2007), Modeling water ice lifetimes at recent Martian gully locations, Geophys. Res. Lett., 34, L09204, doi:10.1029/2007GL029507.
Lai, Y.C., Lerner, D, Williams, K and Crebogi, C. (Nov. 1999) Unstable dimension variability in coupled chaotic systems. Physical Review E 60 (5): 5445-5454 : A.
**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.
Integrated Software for Imagers and Spectrometers Integrated Software for Imagers and Spectrometers
A software library and set of tools to support ingestion, processing, and analysis of planetary science data. Version 8.0.2