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The

Hawaiian Hot Spot

63 points total

Introduction:

Review the text on hot spot volcanism and recall that hotspots produce a string

of dormant volcanoes behind an active volcano. Because we know the age of the

volcanoes and their distance from the hot spot we can use the dormant volcanoes

produced by a hot spot to determine the speed and direction that a tectonic

plate is moving. This exercise will guide you through that process.

There are a couple

of different ways to do this. One would be to recognize that if a dormant

volcano is 5 million years old and is sitting 450 km from a hot spot then it

has moved 450 km in 5 million years. If we divide 450 by 5 we get 90

km/Ma. That unit is kilometers per

million years (Ma is an abbreviation for millions of years). This is not a

particularly useful unit. A million years is a very long time so it’s difficult

to really understand how fast a speed given in km/Ma really is. For most of

what we do we measure speeds in miles per hour. You know how long and hour is

and you know how far a mile is so it’s a useful unit. For Plate tectonic

velocities it’s best to measure the speed in centimeters per year (cm/yr).

Doing this gives a number usually between 5 and 15 or so which is a very useful

and manageable unit. Since there are 100,000 centimeters in a kilometer

converting from km/Ma to cm/yr is relatively easy: divide my 10. So 90 km/Ma is

9.0 cm/yr.

Use the map below

to figure out how fast the Pacific plate has been moving since Oahu formed over

the hot spot. The questions on the next page will guide you through the

process.

How

old are the lava flows on Oahu?

___________ Ma (3 points)

Use

the Map scale to determine how far Oahu is from the hot spot (which is the

brand new underwater volcano Loihi)

___________ km (3 points)

Divide

the distance (#2) by the time (#1) to get a speed for the Pacific plate

___________ km/Ma (5 points)

Now

divide by 10 to convert to cm/yr ___________ cm/yr (5 points)

What

direction did Oahu move as it moved off of the hotspot. This is the direction

that the Pacific plate is moving. _____________

(5 points)

While this

technique is useful it’s limited in that it doesn’t take advantage of all the

data we have. We have age and distance data for the entire Emperor Seamount

Chain as well as the Hawaiian islands. The following exercise will guide you

through the process of using all the available data to learn about the speed

and direction that the Pacific plate has been moving.

First the data.

#

Name

Age (Ma)

Distance

from the hotspot (km)

1

Kilauea

0.20

0

3

Mauna Kea

0.38

54

5

Kohala

0.43

100

6

East Maui

0.75

182

7

Kahoolawe

1.03

185

8

West Maui

1.32

221

9

Lanai

1.28

226

10

East Molokai

1.76

256

11

West Molokai

1.90

280

12

Koolau

2.60

339

13

Waianae

3.70

374

14

Kauai

5.10

519

15

Niihau

4.89

565

17

Nihoa

7.20

780

20

unnamed 1

9.60

913

23

Necker

10.30

1058

26

La Perouse

12.00

1209

27

Brooks Bank

13.00

1256

30

Gardner

12.30

1435

36

Laysan

19.90

1818

37

Northampton

26.60

1841

50

Pearl &

Hermes

20.60

2291

52

Midway

27.70

2432

57

unnamed 2

28.00

2600

63

unnamed 3

27.40

2825

65

Colahan

38.60

3128

65a

Abbott

38.70

3280

67

Daikakuji

42.40

3493

69

Yuryaku

43.40

3520

72

Kimmei

39.90

3668

74

Koko

48.10

3758

81

Ojin

55.20

4102

83

Jingu

55.40

4175

86

Nintoku

56.20

4452

90

Suiko 1

59.60

4794

91

Suiko 2

64.70

4860

One of

the most effective and easiest ways to analyze data is to graph them, so the

first step in our analysis will be to graph the data. You’ve been provided with

graph paper. Graph the age on the X axis (the one on the bottom) and the

distance from the hot spot on the Y axis. (10 points)

Once

you’ve graphed your points draw one straight line that goes through your

‘cloud’ of points. Don’t try to ‘connect the dots’ draw one straight line with

about half your points above and about half your points below the line. It

doesn’t need to be perfect just one straight line that approximates your data.

(5 points)

The

slope of this line is the average speed that the Pacific plate has been moving

over the past 65 million years or so. So let’s calculate the slope of the line.

The slope of a line equals the change in y divided by the change in x for two

points. Even though your line might not go through them it’s easiest to use the

first and last points to do this so look at the data chart and fill in the

appropriate numbers and subtract.

Volcano 91 Suiko 2

age (x) ____________Ma, Distance (y) ____________ km (4 points)

Volcano 1 Kilauea

age (x) ____________ Ma, Distance (y) ____________ km (4 points)

Difference in the x

values ____________ Ma. Difference in the y values ____________ km (4 points)

(Subtract the two numbers above the blanks)

Now divide the

difference in y by the difference in x:

____________km / ____________Ma=____________

km/Ma (4 points)

convert km/Ma to

cm/yr (like you did in question # 4)

Speed of the

Pacific tectonic plate ____________ cm/yr (2 points)

Now that we’ve done

speed, let’s do direction. Look at the map below.

Note that there is

a bend in the seamount chain (labeled bend). The Daikakuji seamount is located

right at the bend.

How

long ago did the bend happen? _________ million years ago (hint: you have a

data set that includes Daikakuji) (3 points)

Keeping in mind how plates move over hot

spots, what direction was the Pacific plate

moving

between the formation of Meiji and

Daikakuji? ________________ (3 points)

What direction has the Pacific plate been

moving since the formation of Daikakuji?

______________ (3 points)

So there you are,

you just used real geoscience data to do what real geoscientists do, you

calculated the speed and direction of a tectonic plate.

Turn the word file

with your answers into the drop box. Photograph or scan the graph name it with

your name and turn it in to the drop box as well.

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