SOIL GEOMORPHOLOGY: WHERE WE STARTED, WHAT WE’VE LEARNED AND WHERE WE ARE HEADED

Soil geomorphology (SG) and weathering studies in North America probably started with the late 1800s to early 1900s work on mid-continent tills, where soils recorded nonglacial intervals. During WW II, the USGS Military Geology Unit had both geologists and soil scientists working on military problems. Their research after the war, along with that of mid-continent workers, helped define modern SG. In the 1960s, some geology and geography departments added SG. Jenny’s 1941 book on soil-forming factors (ClORPT) formed the template for SG. The 1965 USA INQUA meeting showcased SG well. Soil geomorphologists identified geologic vs. pedologic layering (P) in soil profiles, and recognized dust input in all environments. Soil chronosequences (T) have been studied in most climatic regions, so we know how most soils develop with time, climate (Cl), and paleoclimate. Soil catenas (R) also have been studied in many environments, and are useful to assess slope stability. Workers in other fields (neotectonics, archaeology) find SG valuable. New analytical and monitoring techniques over the past 30 years have produced quantitative advances and modeling of soil-forming factors, as well as challenges to SG paradigms. Microbes (O) are far more important in weathering than previously recognized. Laboratory studies of chemical weathering have narrowed the gap between measured field and laboratory rates. Cosmogenic dating, luminescence studies and the ability to analyze milligram quantities of carbon have led to new ways of characterizing soil age. Short-lived isotopes such as ¹³⁷Cs and ²¹⁰Pb allow better measurement of soil mixing and erosion rates. Mass spectrometers have improved climate change interpretation using ¹⁸O and clumped isotope studies of soil carbonate and organic matter. Application of steady-state functions to soils on slopes has returned a focus to long-term SG studies and generates considerable discussion. One paradigm change is that some soils in arid and semiarid landscapes grow upward by dust accretion, protected by desert pavements. And Arctic and peatland soils are globally significant for terrestrial carbon and CH4 budgets.

SG has moved in the direction that Jenny would be proud to have influenced; it will continue to focus on reconstructing the past and guide short-term studies in the critical zone.