Homework #1;	ES 10 -- Geologic Principles	Name___________________

	The goal of this homework exercise is to use steady state box models to investigate the
hydrologic and tectonic systems. Always assume steady state, which means that the total flows
into the reservoir of interest are equal to the total flows out of the reservoir of interest. Remember
that the basic governing equation is F=M/T where F=flows in or out measured in units of mass or
volume/units of time, M=mass, volume, or number of the material or thing of interest, and
T=time. 

Table 1. Distribution of Water on Earth

Surface water
  Lakes and rivers (fresh)		125,000 km3 
  Lakes and inland seas (salty)		104,000 km3 
Groundwater
  Shallow, fresh			4,167,000 km3 
  Deep, salty				4,167,000 km3 
Ice caps and glaciers			29,000,000 km3 
Atmosphere				12,500 km3 
Oceans					1,321,000,000 km3 

Data Source: J.H. Feth, U.S. Geological Survey Circular 601-1, 1973, ÒWater Facts and Figures
for planners and Managers.Ó

Table 2. Flows of water between major reservoirs.

Precipitation
  on land			101,000 km3 /yr
  at sea			299,000 km3 /yr
Evaporation at sea		337,000 km3 /yr
Evapotranspiration 		 63,000 km3 /yr
Discharge from Land to Sea
  from surface waters		32,000 km3 /yr 
  from groundwater		 6,000 km3 /yr

Data Source: W.K. Hamblin and E.H. Christiansen, 1995, ÒEarthÕs Dynamic Systems.Ó

1) Draw the hydrologic system, showing all major reservoirs and flows of water.













2) What is the average residence time of water beneath the surface, i.e., groundwater? Using the
answer as a rough indication, is groundwater a renewable resource? What are the assumptions
implicit in these calculations as applied to the groundwater case?











3) If 60% of the worldÕs trees were cut down, decreasing the rate of evapotranspiration from land
by 30%, how would the rate of precipitation on land be affected? Assume steady state and that the
total amount of water in each of the reservoirs remains constant. How do think your answer would
affect the rest of the trees and plants on Earth.














4) Consider the following information concerning the EarthÕs ocean basins:

Area of oceanic crust:			3.1X108 km2
Average thickness of oceanic crust	8 km
Average age of oceanic crust		30 million years

How much crust must be created each year at divergent margins to produce the EarthÕs oceanic
crust at steady state? Draw a picture to help you figure this out.