EPSS 15 Spring 2017 Introduction to Oceanography Laboratory #1 Maps, Cross-sections, Vertical Exaggeration, Graphs, and Contour Skills MAPS Provide valuable interface to explore the geography of the world Incorporate quantifiable units Have scales equating distances on the surface of the earth with distances on the surface of the map (1cm = 1000km or 1mm =100km) 1
Latitudes are measured from 0 90 degrees north and south of the equator; they mark points of equal angle above and below the equator Parallels of Latitude Maps, continued Longitudes are measured from 0-180 degrees east and west of the prime meridian, which runs from the north to south pole through Greenwich, England Meridians of Longitude Present a side view of the earth Cross-Sections Depth dimension allows for description of the interior of the Earth and subsurface of the oceans. In this class, we are primarily interested in cross-sections illustrating vertical profiles generated through our oceans, and what they can tell us about changes in salinity, temperature, etc and the surface shape of the ocean s floor. The next page shows a portion of an actual cross-section of part of the earth s crust below the town of Santa Barbara, CA. 2
Cross-Sections Elevation Scale: cm = m Distance Fault Geologic formation contact Bedding This was generated using geometric data observed from the surface of the earth between two points, & shows the predicted subsurface geometry of rocks. Cross-Sections Northridge Earthquake Davis & Namson, 1994 Elevation Scale is 1 inch = 500 feet Distance Fault Geologic formation contact Bedding This was generated using geometric data observed from the surface of the earth between two points, & shows the predicted subsurface geometry of rocks. 3
Vertical exaggeration Vertical exaggeration helps maximize the utility of crosssections, especially across large distances. Earth s surface is relatively smooth; if Earth were an egg, the crust of can be equated to the thickness of the eggshell. As a result, cross sections often use vertical exaggeration to show near-surface features. Not vertically exaggerated Vertically exaggerated Vertical exaggeration calculations 1. Find horizontal and vertical scales 2. Then, scale = Distance represented on map Distance represented on earth V.E. = Vertical scale Horizontal scale 3. For example, if vertical scale = 50 cm, and horizontal scale = 50 cm, 10 km 100 km then, V.E. = 50 cm/10 km = 5 = 10 (ten times) 50 cm/100 km 0.5 4
Graphs Visualize relationship between two variables (or more); commonly producing trend lines or curves Graphs are useful 2-d representations of data; data points are plotted on vertical and horizontal axes Graphs can portray linear and nonlinear trends of data Graphs, continued Values, and inferences from the data plot can be gained via interpolation and extrapolation Interpolation = Estimating a value from within the known data plot Extrapolation = Estimating a value from beyond the known data plot (e.g. by extending the trend of the curve fitting the pre-existing data to predict a value generated in space beyond the available plot) Interpolation Extrapolation Today, you ll be working with plotted data values in a nonlinear relationship 5
Contours and Bathymetry Contours are lines connecting data points of equal value (on maps and cross-sections) Examples include the following: Bathymetry (measurement of depths of oceans; e.g. maps on your tables) Topography (e.g. USGS quadrangles, hiking maps) Temperature (e.g. weather maps) Pressure, density, etc. Contours provide spatial knowledge of the earth s surface and ocean floor s surface Contours and Bathymetry Three RULES: 1. Contours never cross one another; you can t be at two different elevations or depths at the same time. 2. A contour can close upon itself; e.g. concentric circles describing a mountain pinnacle, undersea mountain, valley, etc. 3. V s that point uphill are troughs and ones that point downhill are ridges 6
Contours and Bathymetry cont. Bathymetric maps 7