Page 12 - CEGE Spring 2023

FACULTYPROFILE KIMBERLY HILL
Kimberly Hill studies particles that can bring down mountains
Debris flows – rapid, gravity-driven events involving a mixture of
boulders, gravel, sand, and mud –
can cause tremendous loss of life
and property. In January 2023, an article published by Oregon Public Broadcasting (OPB.org) reported “Almost all of the state [California] has received rainfall totals of 400% to 600% above average since Christmas, with some areas receiving as much as 30 inches of precipitation, causing massive flooding. The severe weather has killed at least 19 people since late December. Since New Year’s Eve, the California Department of Conservation’s landslide mapping team has documented more than 300 landslides.” *
Evidence shows that the frequency and hazard of debris flows are increasing, possibly due to changes in climate dynamics (both macro- and microscale). For example, extreme rainfall events increase the erodibility of soil and the driving force of flows. Further, melting permafrost changes soil moisture and permeability. These changes could be linked to dangerous events.
Kimberly Hill studies debris flows. Hill is a physicist in the Department of Civil, Environmental, and Geo- Engineering
(CEGE) and the St. Anthony Falls Laboratory (SAFL) who studies engineering materials, geomorphology, and granular physics problems. More precisely, Hill studies signatures of particle-scale physics in the behavior of natural and manmade infrastructure materials. Specific applications of her research include debris flows in steep upland regions, sediment transport
in rivers, and roadbed materials. Hill focuses her research on understanding the physics of particle-flow processes and applies that understanding to
civil and geophysical infrastructure problems.
Colliding pairs of particles follow relatively simple physical laws that make their motions easy to predict. Bulk flow behaviors, however, are much harder
to predict. For instance, as the particle density increases, as in granular road beds, hot mix asphalt, or muds flowing down steep inclines, the problem of
predicting the motions of the particles in these flows becomes intractable.
To predict behaviors of these complex systems from first principles, one must understand the statistical interactions of particles as well as environmental details, such as local rock properties and relevant climatic details.
Hill’s group researches how climate and rock properties contribute to specific hazards in debris flows. They collect data at debris flow field sites around the globe, from California to Taiwan. Recently, her group traveled to the White Mountains in Owens Valley, California, to collect data from four neighboring debris fans with similar climate histories but vastly different flow signatures. In March 2023, Hill traveled to Taiwan to collect data from twin debris flows in the Laonong River Valley that were deposited under warmer, moister climate conditions.
*Associated Press. (2023) California’s system to defend against mudslides is being put to the ultimate test. Oregon Public Broadcasting. Available at: https://www.opb.org/article/2023/01/15/ california-mudslides-defense-wet-weather-storms-damage/ (Accessed: March 7, 2023).
12 CEGE | CSE.UMN.EDU/CEGE