Hypsographic Curve • Extreme elevations are rare • Two common elevations • Ocean basins (abyssal plains) • Continental interiors Why??
The weight of an Object is determined by its mass and the force of gravity F = the force of gravity (weight) g = the gravitational constant (6.672 x 10-11 N · m2 · kg-2) m1 = the mass of the object m2 = the mass of the Earth r = the distance between the object and the center of the Earth
Weight varies due to three factors 1. Altitude As altitude increases r increases, so F decreases
2. Latitude Weight varies due to three factors
Weight varies due to three factors 3. Local variations in rock density
Geographic Survey of India Mid-19th century Sir George Everest Triangulation systematically disagreed with astronomical near the Himalayas Why?
Each block weighs 2 g density 0.3 0.3 = 0.1 0.5 0.5 0.2 0.2 Water density 1.0 Archdeacon Pratt’s theory of Isostasy
Wood density 0.5 8 g 5 g 5 g 3 g 3 g 2 g 2 g Water density 1.0 Each block weighs 2 g density 0.3 0.3 = 0.1 0.5 0.5 0.2 0.2 Water density 1.0 Astronomer Royal Airy’s theory of Isostasy
Free-Air correction to 0 ft. Uncorrected gravity profile at 20,000 ft. Bouguer Corrected profile