The Hawaiian Hot Spot

125 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.

Speed of Movement of the Pacific Plate

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.

1)

How old are the lava flows on Oahu? ___________ Ma (5 points)

2)

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

underwater volcano Loihi) ___________ km (5 points)

3)

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

___________ km/Ma (5 points)

4)

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

5)

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

6)

One of the most effective and easiest ways to analyze data is to graph them. Plot the values

that describe volcanic islands 83, 86, 90 and 91 onto the graph below. (10 points)

0

10

20

30

40

50

60

70

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Graph 1. Linear relationship between the age of island lava rocks and the distance of the island from

the hotspot

Age of the island lava rocks, in million years (Ma)

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7)

Once you’ve graphed your points use a ruler to draw one straight line that goes

through

the ‘cloud’ of points. Don’t try to ‘connect the dots’ . Instead draw a straight line that

centers about half the data points above the line and about half below. (5 points)

8)

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

past 65 million years or so. 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 on the line. Locate two points on the

line that are easily quantified using the axes. Describe the point highest on the graph first.

Y value of point 1 ____________km X value of point 1 ________________ Ma

Y value of point 2 _____________ km X value of point 2 _______________ Ma

Difference between Y values ____________ km Difference between the X values ____________ Ma

Now divide these differences or changes. Divide the change in y by the change in x :

____________km / ____________Ma=____________ km/Ma (5 points)

Convert km/Ma to cm/yr (like you did in question # 4)

Speed of the Pacific tectonic plate ____________ cm/yr (5 points)

Direction of Movement of the Pacific Plate

. 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.

9)

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

that includes Daikakuji) (5 points)

10)

Keeping in mind how plates move over hot spots, what direction was the Pacific plate

moving between the formation of Meiji and Daikakuji? ________________ (5 points)

11)

What direction has the Pacific plate been moving since the formation of Daikakuji?

______________ (5 points)

Summer of 2018 Eruption of Kilauea Fissure

As of the Summer of 2018, the Kilauea volcano on the Island of

Hawaii

is undergoing a

tremendous eruptive cycle. At the same time, Volcano De Fuego in

Guatemala

has erupted killing

62 people. This exercise will explore both eruptions.

Map of the of the lava flows on Hawaii as of July 9

th

2018

12) Given what you know about Hawaii does it make sense to you that the lava flows are confined

to the southeast side of the island? Why or why not. (hint: think about where the hotspot is. (5

points)

13) The map tells us that there is 11.2 square miles of lava as of July 9

th

. The entire big island has

an area of 4028 square miles. Divide 11.2 by 4028 then multiply that number by 100 to calculate

what percentage of the big island has been covered by the latest eruption.

_____________% of the Big Island. (round it to 3 decimal places) (5 points)

14) Now that a channel has been established lava is reaching the sea from fissure 8, in roughly 13

minutes. Let’s calculate how fast it’s moving in miles per hour

1. Convert 13 minutes to hours. Divide 13 minutes by 60 minutes/hour

13 min

= _____________ hrs (5 points)

60 min/hr

2. It is roughly 8 miles from fissure 8 to the sea. Divide this distance by the travel time you

got above to get the speed the lava is flowing in miles per hour.

Speed =

Distance

=

8 miles

= Speed of the lava _____________ mph. (5 points)

Time _____ hrs

15) Does that number seem fast or slow to you? Do you think that lava would be flowing that fast

if it wasn’t in a channel and was just flowing over open ground? (5 points)

16) Above is a photo of the location of the Fuego Volcano in Guatemala at the edge of the North

American Tectonic plate. How is this tectonic setting different from the Hawaiian volcanoes? (5

points)

17) Read the following article about the Fuego Volcano.

https://www.washingtonpost.com/news/morning-mix/wp/2018/06/04/volcano-erupts-in-

guatemala-killing-at-least-25-injuring-dozens-more/?utm_term=.be27f64a0551

… and the following about the Hawaii eruption.

https://www.express.co.uk/news/world/986439/hawaii-volcano-update-kilauea-eruption-lava-

flow-hazards-latest

How do these two eruptions differ? (5 points)

18) What is the main chemical difference in the composition of the magmas/lavas that is causing

these two events to be so different? (5 points)

19) How is the tectonic setting and type of mantle crust that is generating the magma (noted in

question 16) related to the chemical difference you talked about in question 18? (5 points