19 Descending limbs of convection cells may be present benea

19. Descending limbs of convection cells may be present beneath: a. mid-oceanic ridges b. continental mountain ranges c. shields d. oceanic trenches 20. What mechanisms produce hot, dry climates on the leeward side of mountain ranges? a. Rising moist air on the windward side cools with altitude at a lower rate than dry air b. Dry air warms at a higher rate than moist air moving downslope on the leeward side c. Adiabatic heating and cooling of air is a function of moisture content d. All of the above 21. Gravity is measured by the gal, which has the dimensions of: a. distance b. weight c. force d. acceleration 22. Gravity anomalies indicate differences in: a. topography density of near-surface rocks the shape of the geoid c. d. 23. A gravity correction that reduces the surface to a lab of constant thickness above a hypothetical surface is known as the a. free-air correction b. Bouguer correction d. geoid correction 24. Bouguer gravity anomalies beneath young mountain ranges are usually: a. negative b. positive c. about zero d. highly variable

Solution

Question19

Answer: oceanic trenches

Descending limbs of convection cells may be present beneath Oceanic trenches

Oceanic trenches are very deep seated condition in the oceans whci are by converging plate boundaries in oceanic surface.

Question 20

a) rising moist air on the windward side cools with an altitude at a lower rate than dry air

Question 21

d) acceleration

Question 22

c) Density of near-surface rocks

Gravity Survey - Measurements of the gravitational field at a series of different locations over an area of interest. The objective in exploration work is to associate variations with differences in the distribution of densities and hence rock types. Occasionally the whole gravitational field is measured or derivatives of the gravitational field, but usually the difference between the gravity field at two points is measured. Gravity anomalies are due to the density of substances around (especially underground) the meter. For example, a reading taken over a basaltic dike would show a positive gravity anomaly since basalt is denser than sediments and most rock layers

Question 24

Answer: a Negative

Bouguer gravity anomalies beneath young mountain ranges are usually shows negative anomaly and in oceans it shows positive anomalies.