I heard that Thomas C. Hanks passed away recently. He was a mentor to me. He worked for his career with the US Geological Survey so the memorials of him from his colleagues will be deeper but I wanted to capture some of my memories of him. Tom was very supportive of young scientists and very broad in his scientific thinking. While he was most well known as a seismologist, his work in geomorphology and fault scarps and fragile geologic features was transformative. Look at the nice handwriting (usually from a well sharpened #2 pencil). And the signature THanks. Tom was on my Ph.D. supervisory ..read more

We regulary refer to high resolution topography (HRT) as having Digital Elevation Model (DEM) pixel sizes with their edges less than 1 m. Many raster DEMs derived from airborne laser swath mapping available for example from OpenTopography are delivered at 1m/pix. In many cases, the point density might be high enough to support even higher resolution or smaller pixels. This seems like a fairly simple question: what is the recommended cell size of a DEM for a given point density? The Langridge, et al., 2013 paper cites Hu, 2003 and suggests the following: where S is the estimated cell size (typ ..read more

The fragility of geologic features, such as precariously balanced rocks (PBRs), can be measured by a simple parameter like α. For the case of a PBR is the smallest of the angles between the vertical from the center of mass and its rocking points. In a landscape, each object will have a fragility and so the ensemble will be a fragility distribution. The controls on the initial distribution and its long term evolution will be from the environment and its history (material properties, landscape evolution (lowering), weathering, shaking, etc.). The distribution can be disturbed by an earthquake (o ..read more

For some "light reading" over the winter break, I have enjoyed a read of oral histories of Clarence Allen (Caltech) and Robert Wallace (USGS). EARTHQUAKES, MINERALS AND ME: WITH THE USGS, 1942-1995 by Robert E. Wallace; Oral History Interviews With Stanley Scott; USGS Open-File Report 96-260 Connections EERI Oal History Series: Clarence Allen with interviewer Stanley Scott CLARENCE R. ALLEN (1925-2021) INTERVIEWED BY DAVID A. VALONE Caltech archives. This latter one has a bit more about Caltech and is slightly less polished than the first. Maybe I at times too sentimental, but I found these p ..read more

I saw a link to https://app.wombo.art/ on twitter and people were posting what they got out of using their research or dissertation titles as a prompt. It is pretty amazing. I gave it a try. My dissertation was entitled "Coupled Tectonic Deformation and Geomorphic Degradation along the San Andreas Fault System". I tried that as well as a shorter version "Tectonic Geomorphic San Andreas Fault" with a couple of different styles. I have to ponder the results. Some of the other examples work well when there is an object more recognizeable (such as a bird or T-cell), or somehow I need to give it a ..read more

I recently wrote this memorial for the Geological Society of America Structural Geology and Tectonics Division (which I am now beginning my stint as chairman or soon will). That is the reason for the first person plural. We heard with great sadness and shock of the passing of our dear friend and colleague Professor Paul J. Umhoefer (Northern Arizona University) in late November 2021. Some of us saw him at the 2021 GSA meeting and to lose him so soon after weighs on us. Paul Umhoefer was a great scientist, mentor and teacher, and servant to his professional community and department. He was well ..read more

I heard in late August 2021 that Omar Abdullah was killed in the unrest that is occurring in Ethiopia. I did not learn of any details but he was an embasa--a lion--and no doubt he was there defending his family and lands. He was an amazing guy that I got to know over the years working in the Afar with the Ledi Geraru Project. Others knew him better. I appreciated him very much. He was from the Hadar woreda--administrative area--but we gave him a special title: "camp specialist" so we could keep him employed even when we were working in other areas with other Afars. Even the other Afars grew to ..read more

In April 2021, we finished a fairly intensive project: AC GEO Report on Portfolio Review of EAR Seismology and Geodesy Instrumentation. I defer to that page as the official one, but I wanted to put a note here as well. I was the chair of the committee, and the citation is Arrowsmith, J R., Brodsky, E. E., Cooper, C. M., Elliott, J. L., Fee, D., Fischer, K.M., Hammond, W. C., La Femina, P., Lekic, V., Wang, H., and Worthington, L. L., Recommendations for Enabling Earth Science Through NSF’s Geophysical Facility – A Portfolio Review of EAR Seismology and Geodesy Instrumentation, Report to the U ..read more

The Salt River in central Arizona has a spectactular set of fluvial terraces developed along it. I have lead a number of field trips along the Salt River for outreach and most importantly for our GLG451 Field Geology I course where we use a site along the Salt River for a mapping exercise. I have recently updated the materials associated with that exercise in anticipation of this Spring's class which will include a virtual component. Tour from ASU to the Salt River site. Drone overflight of the key sites for the exercise. I built on some of the very nice writing and descriptions of Professo ..read more

I became obsessed with diffusion erosion modeling in my PhD work. It is a simple (certainly oversimplified) way to think about how hillsloopes may change over time in the absence of mass wasting, debris flow, and fluvial processes. There is a lot to say about it, but I wanted to capture a few items I recently developed. Here is an explanation and assignment on the topic in my Computers in Geology class: Lecture 8: Exploring diffusion using Excel. One of the challenges that I have had in some applications is that the computational "space" was too small in the spreadsheet, given that it is fixed ..read more