Steven W. Anderson

Assessment of Learning in Entry-Level Geoscience Courses: Results from the Geoscience Concept Inventory

Assessment of learning in entry-level college science courses is of interest to a wide variety of faculty, administrators, and policy-makers. The question of student preparedness for college instruction, as well as the effect of instruction on student ideas, has prompted a wide range of qualitative and quantitative studies across disciplines. In the geosciences, faculty are just beginning to become aware of the importance of conceptual change in instruction. The development of the Geoscience Concept Inventory (GCI) and application to the study of learning in entry-level geoscience courses provides a common framework from which faculty can evaluate learning and teaching effectiveness. In a study of 43 courses and 2500 students, we find that students are entering geoscience courses with alternative conceptions (sometimes called “misconceptions”), and in many cases are leaving the classroom with these alternative ideas intact. Comparison of pre- and post-test results show that students with the lowest pre-test scores show the most improvement, whereas those with higher pre-test scores show little, if any, improvement. We also find no relationship between self-reported teaching style and learning as measured by the GCI, suggesting significant research needs to be done to evaluate teaching effectiveness in geoscience classrooms.

Qualitative Analysis of College Students' Ideas about the Earth: Interviews and Open-Ended Questionnaires

Student conceptual understanding and conceptual change is an active area of research in many science disciplines. In the geosciences, alternative conceptions held by students, particularly college students, are not well documented or understood. To further this body of research, students enrolled in introductory science courses at four institutions completed 265 open-ended questionnaires and participated in 105 interviews. Data were collected at a small private university, two large state schools, and one small public liberal arts college. Students were probed on a variety of topics related to the Earths crust and interior, as well as geologic time. Analysis of questionnaire and interview responses indicates that students hold a number of non-scientific ideas about the Earth. Additionally, students apply a range of ontological categories to geologic phenomena, with significant implications for teaching geosciences from a systems perspective.

Crease structures: Indicators of emplacement rates and surface stress regimes of lava flows

Crease structures are features commonly found on lava flow surfaces and consist of a fracture with curved walls that extend outward from a linear valley. These crease structures are found on flows of nearly all compositions and crystallinities. We have mapped the distributions of crease structures on many flows in the western United States and found that (1) axial length is not dependent upon composition and crystallinity; (2) adjacent crease structures are generally aligned in an en echelon pattern; (3) crease structures located adjacent to flow margins are generally perpendicular to these margins; and (4) at Mount St. Helens, Washington, large lobe-bisecting crease structures are found on lobes situated on slopes of less than 20 degrees. A primary surface feature found on many crease structures is striations. Striations are sets of long stripes on the walls of the crease structure that extend approximately parallel to the axis of the central valley, and they appear to be analogous to those found on the faces of cyclically fractured basalt columns. Observations of developing crease structures on 6 of the nearly 20 Mount St. Helens dome lobes show that they form throughout the extrusion of flows situated on slopes of less than 20 degrees, but only at the very beginning and/or end of extrusion of flows on steeper slopes. These observations imply that crease structures form when the lava flow is forced to spread laterally, either as the flow advances over a flat area, or as the down-slope movement stagnates near the end of extrusion (causing the rate of spreading to exceed the downslope rate of flow). This lateral spreading of lava results in the concentration of tensile stress along a line oriented perpendicular to the direction of spreading. The cooled crust of the extrusion is therefore torn apart about this line of tensile stress concentration, forming a central valley that exposes hot, ductile material from the flow interior to the atmosphere. The presence of striations on many crease-structure walls implies that the emplacement mechanism is similar to that suggested for columnar basalts, where each striation is produced by incremental fracturing. The stress responsible for crease structure formation is due to both cooling and lateral spreading of lava. Calculations show that stress due to spreading is three orders of magnitude higher than that due to cooling. Fracture advance times were calculated using a simple one-dimensional conductive cooling model adjusted for the special geometry of the crease structure. The model closely approximates measured crease-structure emplacement times at Mount St. Helens and gives reasonable estimates for crease structures found on older silicic lava flows. We then used this model to calculate emplacement times of entire domes that consist of a single crease structure. By dividing the dome volume by the formation time, we are able to calculate extrusion rates for these older domes. These values, which include the first flow-rate estimates reported for rhyolitic lavas (0.03-106 m 3 /s), similar to average flow rates of 0.7-40 m 3 /s calculated for Mount St. Helens dacite lobes from detailed topographic maps.

PULSED INFLATION OF PAHOEHOE LAVA FLOWS : IMPLICATIONS FOR FLOOD BASALT EMPLACEMENT

Abstract Dilated fractures in Hawaiian pahoehoe lava flows contain three zones that show the kinematics of inflation. The upper columnar zone forms through thermal contraction prior to inflation, the middle planar zone reflects inflation-induced tension, and the lower banded zone contains evidence of brittle and ductile deformation. The formation of the lower banded zone requires varying strain rates during fracture propagation and is best explained by a model where small pulses of lava inject beneath the cooled flow crust through a network of preferred pathways. We demonstrate via simple models of pipe flow that this inflation mechanism is incapable of producing areally extensive continental flood basalts on Earth, although it may explain related features on large Martian volcanoes.

College Student Conceptions of Geological Time and the Disconnect between Ordering and Scale

College student conceptions of the scale of geologic time and the relationships between time and geological or biological events were evaluated through interviews, open-ended questionnaires, and student generated timelines collected from four institutions. Our data indicate students hold a number of alternative conceptions about the Earths formation and the appearance of life, and these ideas are remarkably consistent across institutions. Transferability of these findings was evaluated via comparison with Geoscience Concept Inventory questions related to geologic time collected from 43 institutions nationwide. Detailed evaluation of student timelines reveals a notable disconnect between the relative relationships between the age of the Earth, the time required for the origin of the first life forms (prokaryotes), and the evolution of dinosaurs and humans. Students generally placed these events in the correct relative order, but had a poor understanding of the scale of time between events. Intriguingly, timelines can be mapped onto ternary diagrams, and the relationship between ternary diagram zoning and specific ideas of geologic time is explored. We found that some students, for example those with a young Earth perspective, map onto specific conceptual zones on ternary diagrams.

Mount St. Helens and Santiaguito lava domes: The effect of short-term eruption rate on surface texture and degassing processes

In order to assess the effect of eruption rate on the surface morphology and degassing mechanisms of silicic lava flows, we studied surface characteristics and obtained water content and hydrogen isotopic values of samples from flows at the Mount St. Helens and Santiaguito lava domes. We compared the surface textures and inferred degassing processes to short-term extrusion rates and found that when domes are small and eruption rates are high, lava will not completely degas in transit to the surface, allowing additional volatile loss through surface vesiculation which results in the formation of a scoriaceous carapace. When domes exceed a critical size and/or their cooled crusts reach a critical strength, emergence of new magma is impeded, short-term eruption rates decline, and more thorough degassing can take place leading to smooth-textured flows lacking scoria development. At Mount St. Helens, this transition occurred during the domes third year, when it grew from 31.8 to 53.2 × 106 m3. Santiaguito attained a comparable state after 2–3 years of growth, and for most of its 70-year history has produced non-vesicular lava. Degassing patterns that combine closed, open, and kinetic processes can be distinguished using isotope data obtained from samples whose positions on a flow and emplacement histories are well-constrained. Evidence for these patterns is most clearly preserved in lavas erupted during early, rapid stages of dome growth. Petrologists and volcanologists seeking to infer magma chamber conditions from the volatile contents of extruded lavas thus need to sample flows early in their emplacement while paying attention to surface texture, position relative to the vent and flow front, and time of emergence.

Development of tumuli in the medial portion of the 1983 aa flow-field, Mount Etna, Sicily

A number of tumuli formed on the aa-dominated lava fan complex which developed in the medial zone of the 1983 flow-field of Mount Etna during the later stages of the eruption. This complex flow-field formed on shallow sloping ground below a scarp between 1900 and 1700 m asl. A major tube system fed a branching tube network in the fan complex. Numerous tumuli and break-outs of lava formed in the fan. Three main types of tumulus are identified: (1) Focal tumuli, which are formed from the break-up and uplift of ‘old’, thick lava crust and themselves become sustained sites for the distribution of lava both as flows and within distributary tubes. These focal tumuli are significant centres associated with major tubes. (2) Satellite tumuli, which are typically elongate, whale-back shaped features that branch out from focal tumuli. These satellite tumuli were initially lava flows erupted from a focal tumulus. The crust of the flow slowed or came to a halt and the rigid crust became uplifted and fractured, forming a dome-shaped ridge feature. These satellite tumuli continued to be fed from the focal tumulus and became sites of lava emission with numerous break-outs. (3) Distributary tumuli formed on the fan associated with short-lived break-outs from tubes and are relatively simple structures formed from limited effusion of toey lobes and pahoehoe lava. The major tumuli on the fan complex show distinct dilation fractures. The fracture surfaces provide good exposure of the crust and three distinct zones are recognised – an upper zone showing columnar jointing, a middle zone consisting of planar fracture surfaces and a basal zone with distinctive banded planar fracture surfaces showing evidence of both brittle and ductile formation. Using these data a model is proposed for tumulus growth. Field analysis of the fan complex shows how it was fed by a branching tube system, leading to flow thickening, formation of tumuli and numerous ephemeral boccas.

Block size distributions on silicic lava flow surfaces: Implications for emplacement conditions

We determined block size distributions on the surfaces of Holocene silicic lava flows at the Inyo domes and the Medicine Lake volcano, and studied the development of blocks on the active Mount St. Helens and Mount Unzen lava domes to better understand the emplacement history of young viscous flows. We measured block chord lengths along perpendicular 25 m long transects within vent, jumbled, and ridged morphologic units. Vent regions generally contain the largest average block sizes and largest range of average blocks, whereas ridged areas tend to have the smallest average blocks. Observations at the active Mount St. Helens and Mount Unzen lava domes show that block size distributions reflect stress conditions during flow. High extrusion rates produce small primary blocks and lead to rapid fracturing of the flow surface, whereas low extrusion rates allow large slabs to form in the vent area and lead to less severe fragmentation. A dramatic increase in the size of blocks evident in active vent regions may indicate a significant decrease in eruption rate, and thus could signal the cessation of extrusion. However, if the extrusion rate is too high or the cooling rate too low, a rigid crust and accompanying blocks will not form on an eruptive time scale. Blocks may fracture through mechanical and thermal processes as they move downslope. Most silicic lava flows reach a steady state downslope, where the average block size at the surface remains in the 20–30 cm size range with increasing distance from the vent. Fines (blocks <12 cm) do not accumulate on the flow surface because they slip toward the flow interior through void spaces between surface blocks. We therefore expect long silicic lava flows to have blocky surfaces throughout their lengths, an important consideration for evaluation of planetary lava-flow emplacement.

Emplacement and composition of steep‐sided domes on Venus

Steep-sided domes on Venus have surface characteristics that can provide information on their emplacement, including relatively smooth upper surfaces, radial and polygonal fracture patterns, and pits. These characteristics indicate that domes have surface crusts which are relatively unbroken, have mobile interiors after emplacement, and preserve fractures from only late in their history in response to endogenous growth or sagging of the dome surface. We have calculated the time necessary to form a 12-cm-thick crust for basalt and rhyolite under current terrestrial and Venusian ambient conditions. A 12-cm-thick crust will form in all cases in < 10 hours. Although Venusian lava flows should develop a brittle carapace during emplacement, only late-stage brittle fractures are preserved at steep-sided domes. We favor an emplacement model where early-formed surface crusts are entrained or continually annealed as they deform to accommodate dome growth. Entrainment and annealing of fractures are not mutually exclusive processes and thus may both be at work during steep-sided dome emplacement. Our results are most consistent with basaltic compositions, as rhyolitic lavas would quickly form thick crusts which would break into large blocks that would be difficult to entrain or anneal. However, if Venus has undergone large temperature excursions in the past (producing ambient conditions of 800-1000 K [e.g., Bullock and Grinspoon, 1996, 1998]), rhyolitic lavas would be unable to form crusts at high surface temperatures and could produce domes with surface characteristics consistent with those of Venusian steep-sided domes.

Revisiting the Geoscience Concept Inventory: A call to the community

The use of concept inventories in science and engineering has fundamentally changed the nature of instructional assessment. Nearly a decade ago, we set out to establish a baseline for widespread and integrated assessment of entry-level geoscience courses. The result was the first Geoscience Concept Inventory (GCI v.1.0). We are now retiring GCI v.1.0 and rebuilding the GCI as a more community-based, comprehensive, and effective instrument. We are doing this in the hopes that GCI users, many of whom have expressed a need for a revised and expanded instrument, and the geoscience community at large will view it as a springboard for collaborative action and engagement. If we work together as collaborators, the geosciences have the potential to evaluate learning across our community and over time. INTRODUCTION The Geoscience Concept Inventory (GCI; Fig. 1) was developed to diagnose conceptual understanding and assess learning in entry-level geoscience courses. The GCI has become a staple in many classroom-based research studies, is being revised for use in pre-college settings, and has been shown to discriminate between experts and novices. Although a valuable research tool, the GCI is in need of an expansion that can only be accomplished by a community of geoscientists and educators working together. This paper is a call for that collaboration. The GCI holds a unique place in the concept inventory world for several reasons. First, the GCI is the only concept inventory to generate a bank of correlated concept inventory questions for higher education science (Libarkin and Anderson, 2006). Through this correlation, users of the GCI can create course-specific subtests rather than being tied to a single set of questions. Second, the GCI contains single response, two-tier, and multiple-response multiple-choice questions. Two-tier questions offer added insight into student thinking by requesting an explanation for student responses (Treagust, 1988). Multipleresponse questions, essentially a set of true/false items, are generally more difficult than typical single-response items and are cognitively similar to free response questions, offering deeper insight into cognition (Kubinger and Gottschall, 2007). Third, GCI questions were developed from ideas that both experts and novices found important for entry-level geoscience courses. A review of textbooks provided initial ideas about important concepts for inclusion on the GCI, while open-ended interviews with students provided additional topics (Libarkin and Anderson, 2005). For example, in-depth interviews suggest that students conflate gravity and magnetism and inflate the importance of magnetic fields on the movement of large objects. Addressing this mixing and mis-scaling is important for student understanding of geomagnetism and its effects, a discovery that only became apparent after considering the student perspective. THE NEED TO REVISE AND EXPAND THE GCI AS A COMMUNITY The original GCI questions were piloted with up to 5,000 students enrolled at >40 institutions nationwide, with the current version in use by >200 faculty and researchers. The GCI has been used to estimate learning in geoscience courses, including evaluation of specific instructional approaches (e.g., Kortz et al., 2008) and analysis of learning (e.g., Petcovic and Ruhf, 2008). In ongoing work, GCI scores have been shown to correlate strongly with geological mapping ability. This suggests that the GCI, a measure of very foundational knowledge, can be used as a skills measure to predict performance on an expert task. While we are encouraged that GCI v.1.0 was useful in these studies, we acknowledge that the instrument ingrains our own biases and limitations. As many of our colleagues have stated, the GCI is both an effective instrument for gauging learning in entry-level geoscience courses and a test in need of revision. The diversity of geoscience courses at all levels should be reflected in the assessment instruments used to evaluate learning nationwide. Expansion to more complex, wider ranging questions will allow replicable assessment in advanced courses and across geoscience programs. A critical need for questions targeted toward upper-level courses requires community GSA Today, v. 21, no. 8, doi: 10.1130/G110GW.1 *libarkin@msu.edu Revisiting the Geoscience Concept Inventory: A call to the community GROUNDWORK T H E G EO LO GI CAL SCIETY OF AM ERIC A Furthering the Inf luence of Earth Science