Activity 2.13 A. Figure 2.13 shows the distribution of the Hawaiian Islands Chai

Question

Activity 2.13

A. Figure 2.13 shows the distribution of the Hawaiian Islands Chain and Emperor Seamount Chain. The numbers indicate the average age of the volcano in millions of years (Myr). Obtained from isotopic dating of the basaltic igneous rock of which each island is composed.

1. If both the Emperor and Hawaiian Islands Chains developed as a result of the same mantle hotspot, what is a possible reason that the hotspot trail changes direction at ~ 42 Myr?

2. What was the rate of Pacific motion relative to the Hawaiian hotspot as it was developing the 2.300 km long Emperor Seamount Chain from Myr to 42 Myr? Express the rate in centimeters per year (cm/yr.) In what direction was the plate moving north – relative to the hotspots during that time interval?

3. What was the rate of Pacific Plate motion relative to the Hawaiian hotspot from 5.1 to 0.8 Myr, expressed in cm/year?

4. Using Lo’ihi Seamont as the current location of the Hawaiian hotspot, what was the rate of Pacific Plate motion relative to the Hawaiian hotpot from 0.8 Myr to today, expressed in cm/yr?

Nov. 3, 2002: Mw 7.9 N Denali earthquake March 11, 2011: Mw 9 Tohoku earthquake tsunami, and nuclear Sept. 15, 1994: Huge eruption of Kliuchevskoi volcano. Ash cloud Dec. 23, 1995 Shishaldin olcano sends ash over 10 km high msin 18,000 dead or tends 565 km SE Jan. 17, 1995 Mw 6.9 Kobe, Japan earthquake. 5502 people killed Jan, 17, 1994: Mw 6.7 Northridge earthquake damages 100,000 buildings 72 deaths Juan de June 3, 1991 Unzen, Japan volcanic eruption kills 43 Emperor Seamount Fuca Ridge red) and June 28, 1992 Mw 7.3 Landers earthquake 3 geologists 42 My Chain Kea Volcano June 12, 1991. Mt. Pinatubo, Philippines eruption kills 722 people; volcanic ash cloud extensive (striped) since 1991 Kauai 5.1 Myr 3.4 Myr, O'ahu 1.9 Myr. v1.8 Myr Maui Lana My 8 Myr Mauna Kea PACIFIC OCEAN 4 Myr Hawai'i .Volcanic peaks Knlauea are red on map. Mauna Loa Lö'ihi o.o Myr Seamount 306090|20 150km Figure 2.13 Trail of the Hawaiian hotspot. Top map shows the northen Pacific Ocean, adjacent landmasses, some notable geologic disasters, and the Hawaiian Islands and Emperor Seamount Chains. Lower map shows details of the eastern Hawaian Islands Chain, including locations of major volcanoes. Myr means "million years".

Explanation / Answer

The hot spot trail changes direction at 42 Myr due to a prominent change in the direction of the Pacific plate motion. In the Hawaiian hot spot trail the Hawaii Island are the youngest in the chain. This trail extends 6000 km in length from Hawaiian Island to the Detroit seamount in the northwest Pacific whose age is 80 million years ago. An usual 60 degree band that distinguishes younger Hawaiian chain Island from the older Emperor seamount chain. The bend formed at about 47 million years ago.

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