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Seeing What You Know: How

                                 Researchers’ Backgrounds Have

                                 Shaped the Mima Mound Controversy




         Isaac E. Pope, Science Dept., Centralia College, Centralia, Washington 98531, USA
          As the boundaries of science are pushed   (Tabbutt, 2016). Similar mounds, referred to   Quaternary geologists Robert Logan and
         toward infinity, so has the ever-widening   by Washburn (1988) as “Mimalike mounds,”   Timothy Walsh (Logan and Walsh, 2009).
         divide among ever-deepening disciplines.   have been found extending across the   Rather than resulting from glacial condi-
         Though early scholars often shared a com-  Northwest United States into Midwest North   tions, some suggest mounds were produced
         mon language and context through which to   America and to Africa and beyond (Johnson   from vegetation-anchoring of wind-blown
         filter controversies, the establishment of   and Horwath Burnham, 2012). The discov-  deposits, in some cases following extended
         niche specialties has developed distinct and   ery of Mimalike mounds in a plentitude of   droughts (Seifert et al., 2009). Though pro-
         sometimes competing jargons and philoso-  geologic environments, conditions, and com-  posed  to  explain  mound topography in
         phies that continually morph through time.   positions has led to a range of conjecture   California (Barnes, 1879), Quaternary geol-
         Even so, Earth remains steadfastly interdis-  nearly as diverse as the mounds they describe   ogists in the American Midwest have become
         ciplinary in nature, leading to clashes between   (Johnson and Horwath Burnham, 2012), yet   major advocates of the aeolian model of
         disciplines. Few controversies remain so   each model appears to be largely advocated   mound formation (e.g., Slusher, 1967; Seifert
         entrenched in this divide as the origin of the   by researchers based on their specialty.  et al., 2009).
         Mima mounds.                         Concentrating on the Puget Lowland gla-  On  the other hand, biologists Walter
          Found in the Puget Lowland of Washington   ciation,  J  Harlen  Bretz  proposed  that  the   Dalquest and Victor Scheffer hypothesized
         State, USA, Mima mounds have baffled   Mima mounds had been produced after dif-  that the mounds resulted not from geologic
         geologic thought for over a century (Fig. 1).   ferential melting formed depressions or   activity but by bioturbation. Dalquest and
         Clustering in the thousands along proglacial   “sun cups” in thin sheets of ice along pro-  Scheffer (1942) proposed that a sandy loam
         terraces, the Mima mounds are domelike   glacial terraces, which were later filled with   overlying the proglacial terraces became a
         ellipsoids composed of a sandy loam overly-  sediment and left as mounds after the ice   locally thickened biomantle around activity
         ing relatively impermeable coarse-bedded   melted (Bretz, 1913). Though dissatisfac-  centers of burrowing rodents. This idea has
         gravels (Pope et al., 2020; Pringle and   tory to Bretz as a comprehensive explana-  become a favorite among biology and geog-
         Goldstein, 2002; Goldstein and Pringle,   tion for the Mima mounds, the sun cups   raphy researchers in the Mima mound con-
         2020). Up to 2 m high and 12 m in diameter,   hypothesis has been revived several times,   troversy and has been applied to a number
         the mounds are elongated parallel to the   such as by pedology graduate student R.C.   of sites in North America and elsewhere (see
         downslope gradient of the host terraces   Paeth (Paeth, 1967) and most recently by   Johnson and Horwath Burnham, 2012).
                                                                                  The most recent model to have been
                                                                                developed was forwarded by Andrew Berg,
                                                                                a geologist in Washington State. Berg (1990)
                                                                                proposed that earthquakes mobilized loose
                                                                                sediment  into  concentrated  heaps,  forming
                                                                                mounds. Though the hypothesis has not been
                                                                                further developed in the literature, it has
                                                                                amassed a following of Pacific Northwest
                                                                                geologists, particularly those interested in
                                                                                earthquakes and volcanism resulting from
                                                                                the Cascadia Subduction Zone.
                                                                                  While most advocates adhere to models
                                                                                relying on data within their discipline, some
                                                                                models have been overturned by experts
                                                                                within the same field. A popular model in the
                                                                                mid-twentieth century propounded that
                                                                                mound topography resulted from polygonal
                                                                                permafrost cracking and subsequent melting
        Figure 1. At their type locality in Washington State, Mima mounds are a locally thickened sandy loam   of ice wedges, as seen in current periglacial
        up to 2 m high, clustering along proglacial terraces. Similar mounds have been found across the world   environments. Eminent periglacial geologist
        in a plentitude of geologic environments, which has led to a range of hypotheses nearly as diverse as
        the mounds they describe.                                               A.L. Washburn organized a conference in the

         GSA Today, v. 31, https://doi.org/10.1130/GSATG493GW.1. CC-BY-NC.

         34  GSA Today  |  June 2021
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