Geological Wiki-Hole
I just escaped a geological wiki-hole. I read about the Cascade Arc (home of the only historical eruptions in the United States), Mount Rainier (a surprisingly prominent mountain), plutons (subterranean crystallized igneous rock intrusions), the Volcanic Explosivity Index (Yellowstone tops the scale), Puget Sound (a flooded glacial fjord system), the most prominent peaks in the United States (fun to play with the table sorting), the Yellowstone Caldera (every 600k to 900k years; last one was 640k years ago), topographic prominence and isolation. Among many other things.
Isolation is probably the coolest thing I learned tonight, because of how a list of isolated peaks gives you a nice cover of an area, a division of peaks that doesn't favor one or another region too much (especially Alaska or Colorado). Topographic isolation is the distance before you reach a point of higher elevation. So for the United States you start at Mt. McKinley (Alaska). Then you fly far off to Mauna Kea (Hawaii), to Mount Whitney (California), to Mount Mitchell (North Carolina), to Mount Washington (New Hampshire) and to Mount Rainer (Washington). It's basically like demarcating a watershed.
I am also enamored of prominence. You find prominence by going down in contour lines until you reach a ring that contains a point of higher elevation. The easiest explanation is via rising sea level. To find a peak's prominence you raise sea level until it is the highest point on its island. The prominence will be the height of the peak above that imaginary sea level. It has to be specially defined for Mt. Everest, since nothing is higher. Every other peak is recursive. The most prominent peaks in the United States are Mount McKinley, Mauna Kea and Mt. Rainier.
Science and the internet… a dangerous combination.