geology 103h exam 1

GPS

• global positioning system

• one of the several space based radio navigation systems

Steven Callahan

• wrote Adrift

• 76 days lost at sea, got lost after departing Newport, RI

What are the most basic tools to navigating at sea?

protractor and a watch

polynesian navigation

used wayfinding techniques, such as navigation by the stars, observation of birds, ocean swells, and wind patterns

How did they know the Earth is a sphere?

• projected shadow of the Earth on the moon is always round

• you see a different set of stars if you travel north or south

• the sun is not overhead in every place at the same time during noon

How was Earth’s circumference calculated?

Eratosthenes used trigonometry to calculate the angle of the sun at 2 cities 500 miles apart

latitude

• parallel to the Equator

• North and South is 0 degrees

• mapped by 30 degree increments

• 1 degree lat = 60 nautical miles

• 1 minute lat = 1 nautical mile

longitude

• parallel to the Prime Meridian

• East and West

• Greenwich, Englad is 0 degrees

piloting

earliest method of navigation, judging by local landmarks, and only works within sight of coastline

dead reckoning

process of estimating current position based on a previously determined position and estimated speed over elapsed time

errors are cumulative, so it can go wrong (Honda Point)

celestial navigation

determines angle between the horizon and the North Star, measured with a sextant

chronometer

used to measure time to calculate longitude

using time to calculate longitude

(difference between your time and GMT)*(15 degrees longitude per hour) = your longitude

behind GMT = W, ahead of GMT = E

How much of the seafloor has been mapped?

28.3%

Why map the seafloor?

• safety of navigation

• aid search/rescue efforts

• resource exploration and exploitation

• modeling ocean processes

bathymetry

measurement of ocean depths and the charting of the shape or topography of the ocean floor

mariana trench

deeper than mt. everest is tall, contains the Challenger Deep which is the deepest place in the worlds ocean

soundings

earliest measure of water depth, weighted lines were lowered from ships

topographic maps

depicts 3-D surfaces in 2-D, using contour lines to show equal elevation

bathymetric charts

underwater topographic map, uses isobaths to show equal elevation

echo sounding

measures ocean depth, high frequency sound waves travel through water, reflect off the sea floor and are recorded by the hydrophone (2D profiles of the seafloor)

calculating depth equation

d = v(t/2)

multi-beam surveying

provides an incredibly detailed imagery of the seabed through reflectivity measurement

sidescan sonar

images a 60 km swath of the seafloor, uses the intensity of the return signal

seismic reflection profiling

used to “see” structures below the seafloor, lower frequency energy source, deep penetration into sedimentary layers and ocean crust

satellites

precise altimeters can map the relief of the ocean surface with centimeter-scale resolution

EEZ

Exclusive Economic Zone, 200 mile zone that is controlled by all coastal countries

Seabed 2030

international mapping effort that is trying to make a better map of the seafloor

Earthquake Energy

measured on the Richter scale, a base-10 logarithmic scale, measured in microns

Earthquake Epicenter

seismic waves radiate away from their point of origin (focus) in all directions, the epicenter is the point on the surface above the focus

compressional waves

P-waves, travel fast through Earth

shear waves

S-waves, are slower and can’t travel through liquids

surface waves

rayleigh waves. travel along Earth’s surface

density

how much matter is in a certain volume

how do we know that the outer core is liquid?

• measuring S and P waves during an earthquake

• shows that the layers have different densities

lithosphere

rigid outer layer including the crust and upper most mantle