Lab 8: Mapping - Landforms on Contour Maps - Noses


Contours that show a "nose" sweep around a turn. Scan your eyes around the z values on this map to find the points with 2311 and 2312 z values. Z values fall off from this area toward the top, left, and bottom, and other values above 2300 are restricted to the lower right area of the map:



A "nose" is an area of bending contours around an elongate shape. A nose may be thought of as a form of ridge, and is often at the end or a ridge. The contour map for this nose shows a little closure around the point with z value of 2312, sort of like a wart on the end of the nose (eeeww):



Why is a nose called a nose? Well, look in the mirror and imagine drawing contours on your nose. If you need a little help, here's a head with horizontal planes (parallel to the floor):



Imagine that we were contouring this head, we would draw contour lines, which are lines of equal value, in this case height above the floor at these "elevation" planes. This is an opportunity to appreciate another way of defining contour lines: the lines of intersection between surfaces. The surface of a head -- the skin surface -- is one surface. An individual planar surface at a given elevation, in this case for distance above the floor, is another surface. Two surfaces that intersect will have a line of intersection. We are looking at this to learn about the term nose, so let's focus on the contour lines that would cross the nose, with the head rotated a little to allow viewing from above:



If you contour a person's face, the contours running across the nose will sweep out and around the bridge of the nose. Look at the intersections of the two planes with the nose -- those would be the contour lines. Look at the bottom plane, where it intersects the skin surface. A line of intersection sweeps across a cheek, then out and around the nose, then across the other cheek.  The "out and around" part forms a contour of the "nose."


A nose is no insignificant feature on a face. Neither is it insignificant in geology. A nose on a surface topography map could represent a giant type of "hill" extending for miles. A nose on a contour map of an underground layer could show a spot where great quantities of oil and gas are trapped. You will learn elsewhere around geological structures called anticlines which are formed by layers of rock forming a "total" fold -- imagine flopping a blanket over the back of a couch -- the blanket would go up and over the back of the couch forming an anticlinal fold. A nose is a subtler feature than an anticline, forming only a "bump" on a surface (if your face had no nose, it would be flat in front, but it has a nose as a kind of "bump" on your head). Nevertheless, a nose can be a large structure with enough form to effectively trap oil and gas, just as anticlines do in more dramatic fashion.