EPSS 15 Fall 2017 Introduction to Oceanography Laboratory #1 - PDF document

10/4/17 EPSS 15 Fall 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

10/4/17 Maps, continued • Latitudes are measured • Longitudes are measured from 0 – 90 degrees north from 0 - 180 degrees east and south of the equator; and west of the prime they mark points of equal meridian, which runs from the angle above and below the north to south pole through equator Greenwich, England Meridians of Longitude Parallels of Latitude Cross-Sections •Present a side view of the earth •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

10/4/17 Cross-Sections Map by P. Coney 3 - 2 - 1 - 0 - 0 10 20 30 40 Elevation Distance (kilometers) (kilometers) Scale: __cm = __km •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 (meters) Distance Scale is 1 inch = 500 feet (meters) 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

10/4/17 Vertical exaggeration • Vertical exaggeration helps maximize the utility of cross- sections, 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 Distance represented on map scale = Distance represented on earth 2. Then, Vertical scale V.E. = Horizontal scale 3. For example, if vertical scale = 50 cm , and horizontal scale = 50 cm , 10 km 100 km = 10 (ten times) then, V.E. = 50 cm/10 km = 5 50 cm/100 km 0.5 4

10/4/17 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 non- linear 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

10/4/17 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

10/4/17 Contours and Bathymetry cont. Bathymetric maps 7