Page 67 - Laboratory Manual in Physical Geology

N
Sept. 15, 1994: Huge eruption of
Kliuchevskoi volcano. Ash cloud Dec. 23, 1995: Shishaldin
extends 565 km SE volcano sends ash
over 10 km high
Jan. 17, 1995:
Kobe, Japan earthquake. Jan. 17, 1994: Northridge
5000 people killed 60 m.y. earthquake damages
100,000 buildings
Juan de
June 3, 1991: Emperor Fuca Ridge
Unzen, Japan volcanic Seamount (red) and
eruption kills 41 people, chain plate
including June 28, 1992: Most
3 geologists powerful earthquake
40 m.y. in 40 years
Kilauea Volcano
Hawaiian Islands chain
erupts continuously
June 12, 1991: Mt. Pinatubo, since 1991
Philippines eruption kills 1 person;
volcanic ash cloud extensive (striped) Enlarged
below
Kauai N

Nihau 4.7

Oahu

2.5 H A W A I I A N I S L A N D S C H A I N
Molokai
1.6
Maui
P A C I F I C O C E A N Lanai 1.1
Mauna Kea
Volcano
Average age
(millions of years)
0.0 Hawaii
Erupting
Volcanic peaks now
are red on map.
Mauna Loa
Volcano Kilauea
0 30 60 90 120 150 km Volcano

FIGURE 2.7 Effects of a hot spot on the Pacific seafloor. Top map shows the northern Pacific Ocean, adjacent landmasses, some

notable geologic hazards (natural disasters), the Hawaiian Islands chain, and the Emperor Seamount chain. Lower map shows details of the
Hawaiian Islands chain, including locations of volcanic peaks.

Pressure (P) Confining Pressure. Atoms and molecules of air
When you press your hand against something like a (atmosphere) are masses of matter that are pulled by
bookshelf, you can apply all of your body weight against gravity toward the center of Earth. But they cannot
the surface area under your hand. Therefore, pressure reach Earth’s center because water, rocks, and your
is expressed as amount of weight applied per unit of body are in their path. As a result, the weight of the air
area. For example, imagine that you weigh 100 pounds presses against surfaces of water, rocks, and your body.
and that your hand is 5 inches long and 4 inches wide. If you stand at sea level, then your body is confined by
If you exert all of your weight against a wall by leaning 14.7 pounds of weight pressing on every square inch
2
against the wall with one hand, then you are exerting of your body (14.7 lbs/in ). This is called atmospheric
100 pounds of weight over an area of 20 square inches confining pressure . Scientists also refer to this as one
(5 inches 4 inches 20 square inches). This means atmosphere (1 atm) of pressure.
that you are exerting 5 pounds of pressure per square inch You do not normally feel one atmosphere of confining
of your hand. pressure, because your body exerts the same pressure to
keep you in equilibrium (balance) with your surroundings.

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