STUDENTS' DIFFICULTY IN VISUALIZING THE HORIZONTAL MAY CONTRIBUTE TO DIFFICULTY ON GEOLOGICAL STRIKE AND DIP TASKS

To help students visualize strike and dip, many newer textbooks illustrate strike by showing a shoreline where a horizontal water surface intersects a sloping rock surface, and dip by showing water flowing down a sloping surface. Textbook illustrators apparently presume that students will find it obvious that the water surface is horizontal, that the planes of the water surface and the dipping rock intersect to form a horizontal line, and that water flows down the steepest available path. However, extensive cognitive research shows that many people have difficulty visualizing horizontal and vertical surfaces, including the horizontal surface formed by a body of water. In the widely-used water level test (WLT), respondents are shown a drawing of an empty, tilted bottle and asked to draw a line to show where the water would be if the bottle were about half full. Many adults, especially females, perform poorly on this test. We hypothesized that students who struggle with this WLT task would likewise struggle with strike and dip.

Undergraduate psychology students (N=152) were given instruction on strike and dip using a modified version of a U.S. Geological Survey lesson. They were taken to an artificial plywood “outcrop” and were asked to mark strike direction, dip direction, and dip angle on a map of the immediate vicinity. On another map, they were asked to mark the orientation of a rod placed on flat ground. Students also responded to new 3-D horizontality and verticality tasks by marking shorelines and the paths of falling water-drops on slanted plexiglass surfaces. Most dramatic was the finding that there were substantial errors on all measures. On the strike task, 41% of the students' answers differed from the correct answer by 30° or more. On the dip angle, 43% of the students' answers differed from the correct answer by 20° or more, with the modal answer of 45° being substantially steeper than the correct answer of 30°. Even on the rod task, where there was no need to visualize an imaginary horizontal line, 34% of answers were off by 30° or more. Performance on the standard (2-D) WLT was a strong predictor of performance on the rod task and the 3-D WLT, but not the strike task. Data are consistent with the hypothesis that basic spatial concepts, including horizontality and verticality, are important for mastering geology lessons.