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Ranking Features Based on Magnitude of Change

The existence of these topographic change features is well documented and they are likely well known to communities in their vicinity, so their delineation is not new information. What is new information, perhaps, is their ranking compared to other similar features across the United States. Viewing of these examples is also useful for learning about the performance and results of the topographic change detection process developed and applied in this study.

The following figures present the individual topographic change polygons that are top ranked in terms of one or more parameters. Not surprisingly, each of these features is associated with large surface mining operations.

In the next five images, it is clear that some of the features represent an expansion of the mining activity that was already evident when the source data for the NED were collected. In these cases, the changes in elevation resulting from continued earth moving were enough to be detected as significant surface transformations, even when the area was already in a disturbed condition.

Top ranked topographic change polygon (outlined in yellow): largest cut area (8.75 km2) and largest cut volume (1.25 x 10⁹ m3). This feature is the Bingham Canyon copper mine in north central Utah. From left to right, the images are NED shaded relief, SRTM shaded relief with change polygons overlaid (blue = cut; red = fill), and Landsat image. The dates of the source data for the NED and SRTM are shown. This area is about 5.5 km east-west by 9.7 km north-south.

Top ranked topographic change polygon (outlined in yellow): largest fill area (9.79 km2). This mining feature is located in the Iron Range in northern Minnesota near the town of Mountain Iron. From left to right, the images are NED shaded relief, SRTM shaded relief with change polygons overlaid (blue = cut; red = fill), and Landsat image. The dates of the source data for the NED and SRTM are shown. This area is about 5.5 km east-west by 9.7 km north-south.

Top ranked topographic change polygon (outlined in yellow): largest mean elevation change for a fill (104.6 m). This feature is located at the Morenci copper mine near Clifton in southeastern Arizona. From left to right, the images are NED shaded relief, SRTM shaded relief with change polygons overlaid (blue = cut; red = fill), and Landsat image. The dates of the source data for the NED and SRTM are shown. This area is about 5.5 km east-west by 9.7 km north-south.

Top ranked topographic change polygon (outlined in yellow): largest mean slope change for a cut (33.2°). This feature is the Sacaton copper mine located in south central Arizona. From left to right, the images are NED shaded relief, SRTM shaded relief with change polygons overlaid (blue = cut; red = fill), and Landsat image. The dates of the source data for the NED and SRTM are shown. This area is about 5.5 km east-west by 9.7 km north-south.

Top ranked cut polygon based on the combined ranks for area, volume, and change in elevation, relief, slope, and aspect (outlined in yellow). This feature is located at the Mission copper mine near San Xavier, Arizona. From left to right, the images are NED shaded relief, SRTM shaded relief with change polygons overlaid (blue = cut; red = fill), and Landsat image. The dates for the NED and SRTM source data are shown. This area is about 5.5 km east-west by 9.7 km north-south.

The following three example areas appear to have no evidence of surface modification in the NED data, thus the mining was initiated some time after the date of the NED source material. The date of the NED source material refers to the date of the information (quadrangle map or aerial photography) from which the USGS 7.5-minute DEM was derived.

Top ranked topographic change polygons (outlined in yellow): largest fill volume (5.16 x 108 m3), largest mean elevation change (–177.3 m), and largest relief change (263.7 m) for a cut. This feature is a gold mining operation near Rodeo Creek in north central Nevada. From left to right, the images are NED shaded relief, SRTM shaded relief with change polygons overlaid (blue = cut; red = fill), and Landsat image. The dates of the source data for the NED and SRTM are shown. This area is about 5.5 km east-west by 9.7 km north-south.

Top ranked topographic change polygon (outlined in yellow): largest relief change for a fill (73.5 m). This feature is located at the Inspiration copper mine near Miami in southeastern Arizona. From left to right, the images are NED shaded relief, SRTM shaded relief with change polygons overlaid (blue = cut; red = fill), and Landsat image. The dates of the source data for the NED and SRTM are shown. This area is about 5.5 km east-west by 9.7 km north-south.

Top ranked fill polygon based on the combined ranks for area, volume, and change in elevation, relief, slope, and aspect (outlined in yellow). This feature is located at the McCoy, Nevada, open pit gold mine. From left to right, the images are NED shaded relief, SRTM shaded relief with change polygons overlaid (blue = cut; red = fill), and Landsat image. The dates of the source data for the NED and SRTM are shown. This area is about 5.5 km east-west by 9.7 km north-south.

By assigning quantitative attributes to individual change features based on the elevation and difference datasets, comparisons can be made with other well-known features. The alteration to Mount St. Helens as a result of its 1980 eruption is often cited as an example of topographic change, a catastrophic natural transformation in this case. After the eruption, the USGS constructed a new DEM that, when paired with the DEM representing pre-eruption conditions, shows the value of multitemporal elevation data. See http://ned.usgs.gov/Ned/historic.asp.

The individual feature mapped in this study with the greatest volume change is the Bingham Canyon copper mine in Utah, with a volume of 1.25 x 10⁹ cubic meters (see figure below). Although this amount is more than twice the volume of the second ranked feature (the cut at the Rodeo Creek, Nevada, gold mine), the volume of material removed from Mount St. Helens (2.83 x 10⁹ cubic meters) is nearly 2.3 times greater than the volume removed at Bingham Canyon.

Top ranked topographic change polygon (outlined in yellow): largest cut area (8.75 km2) and largest cut volume (1.25 x 10⁹ m3). This feature is the Bingham Canyon copper mine in north central Utah. From left to right, the images are NED shaded relief, SRTM shaded relief with change polygons overlaid (blue = cut; red = fill), and Landsat image. The dates of the source data for the NED and SRTM are shown. This area is about 5.5 km east-west by 9.7 km north-south.

Geomorphic events with a magnitude like that of Mount St. Helens are rare, at least within a human lifetime, thus they attain much notoriety. As such, they are often used to give context to other similar phenomena. The total volume of material displaced as calculated in this study (4.33 x 10¹⁰ cubic meters) equates to more than 15 times the volume moved in the Mount St. Helens eruption. As a side note, even though the largest man-made geomorphic feature (Bingham Canyon mine) detected in this study equates to less than half the amount of material moved in the 1980 Mount St. Helens eruption, it contributes nearly 3 percent of the total volume of materials moved as calculated in this study. Given the fact that the Bingham Canyon mine is just one of 5,263 features in the topographic change inventory, that percentage is quite significant.