ROCK STARS: Johannes Walther, p. 12 VOL. 21, NO. 8 A PUBLICATION OF THE GEOLOGICAL SOCIETY OF AMERICA AUGUST 2011 Inside: L 2010–2011 Congressional Science Fellow Report: Interesting Times, Part 2, p. 18 L 2011 GSA Annual Meeting & Exposition Lunchtime Lecture Highlights, p. 22 L Groundwork: Revisiting the geoscience concept inventory: A call to the community, p. 26 Not Just Software. RockWare. For Over 28 Years. 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RockWare.com VOLUME 21, NUMBER 8 ▲ AUGUST 2011 SCIENCE ARTICLE GSA TODAY (ISSN 1052-5173 USPS 0456-530) prints news and information for more than 23,000 GSA member read- ers and subscribing libraries, with 11 monthly issues (April/ May is a combined issue). GSA TODAY is published by The 4 Understanding Earth’s eroding surface Geological Society of America® Inc. (GSA) with offices at with 10Be 3300 Penrose Place, Boulder, Colorado, USA, and a mail- ing address of P.O. Box 9140, Boulder, CO 80301-9140, USA. Eric W. Portenga and Paul R. Bierman GSA provides this and other forums for the presentation of diverse opinions and positions by scientists worldwide, The Three Sisters are iconic sandstone towers regardless of race, citizenship, gender, sexual orientation, Cover: religion, or political viewpoint. Opinions presented in this exposed above the Jamison Valley in the Blue Mountains, publication do not reflect official positions of the Society. Australia. Erosion in the mountains is dominated by © 2011 The Geological Society of America Inc. All rights stream channels cutting through exposed joints and reserved. Copyright not claimed on content prepared wholly preferential erosion of weaker shale units interbedded by U.S. government employees within the scope of their within the Triassic-aged sandstone. Photo by Eric Portenga. employment. Individual scientists are hereby granted per- See related article, p. 4–10. mission, without fees or request to GSA, to use a single fig- ure, table, and/or brief paragraph of text in subsequent work and to make/print unlimited copies of items in GSA TODAY for noncommercial use in classrooms to further education and science. In addition, an author has the right to use his or her article or a portion of the article in a thesis or disserta- –– tion without requesting permission from GSA, provided the bibliographic citation and the GSA copyright credit line are 12 ROCK STARS: Johannes Walther (1860–1937): More than the Law of given on the appropriate pages. For any other use, contact [email protected]. Facies Correlation Subscriptions: GSA members: Contact GSA Sales & Service, +1-888-443-4472; +1-303-357-1000 option 3; gsaservice@ 14 Go EarthTrek! geosociety.org for information and/or to place a claim for non- receipt or damaged copies. Nonmembers and institutions: 16 2011 GSA Section Meeting Mentor Program Highlights GSA TODAY is free with a paid subscription to GSA Bulletin, Geology, Lithosphere, and Geosphere (all four journals); otherwise US$70/yr; to subscribe, or for claims for non-receipt 18 2010–2011 GSA-USGS Congressional Science Fellow Report: Interesting and damaged copies, contact AIP Customer Service, subs@ aip.org. Claims are honored for one year; please allow suffi- Times—Part 2 cient delivery time for overseas copies. Periodicals postage paid at Boulder, Colorado, USA, and at additional mailing 19 2011–2012 GSA-USGS Congressional Science Fellow Named offices. Postmaster: Send address changes to GSA Sales & Service, P.O. Box 9140, Boulder, CO 80301-9140. 2 0 GSA Foundation Update GSA TODAY STAFF Executive Director and Publisher: John W. Hess 22 2011 GSA Annual Meeting & Exposition Lunchtime Lecture Highlights Science Editors: Bernie Housen, Western Washington Univ. Geology Dept. (ES 425) and Advanced Materials Science and 23 2011 GSA Annual Meeting & Exposition Presidential Address & Awards Engineering Center (AMSEC), 516 High Street, Bellingham, WA 98225-9080, USA, [email protected]; R. Damian Nance, Ceremony Ohio University Dept. of Geological Sciences, 316 Clippinger Laboratories, Athens, OH 45701, USA, [email protected] 25 Classifi ed Advertising Managing Editor: K.E.A. “Kea” Giles, [email protected], [email protected] 26 Groundwork: Revisiting the Geoscience Concept Inventory: A Call to the Graphics Production: Margo Sajban Community Advertising (classifieds & display): Ann Crawford, +1-800- 472-1988 ext. 1053; +1-303-357-1053; Fax: +1-303-357-1070; –– [email protected]; [email protected] GSA Online: www.geosociety.org Erratum GSA TODAY: www.geosociety.org/gsatoday/ On p. 12 of the July 2011 GSA Today, the affiliation for newly elected GSA Fellow R. Printed in the USA using pure soy inks. Laurence Davis was listed as the College of Mt. St. Joseph; however, R.L. Davis is at the University of New Haven. GSA Today regrets this error. Understanding Earth’s eroding surface with 10Be Eric W. Portenga, Dept. of Geology, University of Vermont, 180 rates at 87 sites around the world. Here, we compile, normalize, Colchester Ave., Burlington, Vermont 05405, USA, eporteng@ and compare published 10Be erosion rate data (n = 1599) in order uvm.edu; Paul R. Bierman, Dept. of Geology and Rubenstein to understand how, on a global scale, geologic erosion rates inte- School of the Environment and Natural Resources, University of grated over 103 to 106 years vary between climate zones, tectonic Vermont, 180 Colchester Ave., Burlington, Vermont 05405, USA, settings, and different rock types. [email protected] Drainage basins erode more quickly (mean = 218 m Myr−1; median = 54 m Myr−1) than outcrops (mean = 12 m Myr−1; median = 5.4 m Myr−1), likely reflecting the acceleration of rock weathering ABSTRACT rates under soil. Drainage basin and outcrop erosion rates both For more than a century, geologists have sought to measure the vary by climate zone, rock type, and tectonic setting. On the global distribution of erosion rates on Earth’s dynamic surface. Since the scale, environmental parameters (latitude, elevation, relief, mean mid-1980s, measurements of in situ 10Be, a cosmogenic radionu- annual precipitation and temperature, seismicity, basin slope and clide, have been used to estimate outcrop and basin-scale erosion area, and percent basin cover by vegetation) explain erosion rate Figure 1. Geographical distribution of cosmogenic 10Be erosion rate data (see supplemental data Tables DR1–DR3 [see text footnote 1]). (A) Location of studies compiled in this paper. (B) Distribution of outcrop samples and (C) drainage basin samples. Symbols sized to reflect the number of samples per study and colored to indicate relative erosion rate. Note: Citations included within this figure are listed with the supplemental data text. GSA Today, v. 21, no. 8, doi: 10.1130/G111A.1 4 AUGUST 2011, GSA TODAY variation better when they are combined in multiple regression and Steig, 1996; Brown et al., 1995; Granger et al., 1996; Nishiizumi analyses than when considered in bivariate relationships. Drainage et al., 1986; Schaller et al., 2001; Small et al., 1997). basin erosion rates are explained well by considering these envi- The method relies on the observation that cosmic rays interact ronmental parameters (R 2 = 0.60); mean basin slope is the most with Earth’s surface, producing 10Be, an otherwise exceptionally powerful regressor. Outcrop erosion rates are less well explained rare isotope. The production of 10Be occurs predominantly within (R 2 = 0.32), and no one parameter dominates. The variance of ero- a few meters of Earth’s surface and decreases exponentially with sion rates is better explained when subpopulations of the global depth. Thus, the concentration of 10Be in outcropping rock or in data are analyzed.