As a lithospheric plate moves over a hotspot in the upper mantle below the plate

Question

As a lithospheric plate moves over a hotspot in the upper mantle below the plate, a volcano develops directly above the hot spot. As the plate continues to move, the volcano drifts away from the hotspot and eventually becomes dormant. Meanwhile, a new volcano develops over the hotspot next to the older volcano. The result is a trail of volcanoes with one end of the line located over the hot spot and quite active and the other end distant and inactive. In between is a succession of volcanoes that are progressively older with distance from the hot spot.

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 Plate motion relative to the Hawaiian hotspot as it was developing the 2,300 km long Emperor Seamount Chain from 65 Myr to 42 Myr? Express the rate in centimeters per year (cm/yr.). In what direction was the plate moving north—relative to the hotspot 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 Seamount as the current location of the Hawaiian hotspot, what was the rate of Pacific Plate motion relative to the Hawaiian hotspot from 0.8 Myr to today, expressed in cm/yr?

Nov. 3, 2002: Mw 7.9 N Dena euake Sept. 15, 1994: Huge eruption of Kliuchevskoi volcano. Ash cloud Dec. 23, 1995: Shishaldin olcano sends ash over 10 km high March 11, 2011: Mw9 Tohoku earthquake, extends 565 km SE tsunami, and nuclear Jan. 17, 1994: Mw 6.7 Northridge earthquake damages 100,000 buildings 72 deaths crisis; >18,000 dead or missing Jan. 17, 1995: Mw 6.9 65 Myr Kobe, Japan earthquake. Juan de Fuca Ridge (red) and plate 5502 people killed Emperor Seamount chain June 3, 1991: Unzen, Japan volcanic eruption kills 43 people, including 3 geologists June 28, 1992: Mw 7.3 Landers earthquake -42 Myr Hawaiian islands chain erupts continuously since 1991 June 12, 1991: Mt. Pinatub Philippines eruption kills 722 people; volcanic ash cloud extensive (striped) Enlarged below Kaua'i HA WA II 5.1 Myr Ni'hau A N ISLANDS 3.4 Myr, O'ahu Molokai 1.9 Myr1.8 My Maui CH 1.3 Lana' Myr 08 Myr Mauna Kea Volcano PACIFIC OCEAN Hawai'i 0.4 Myr Kilauea Volcano Volcanic peaks are red on map Mauna Loa Volcano Lo ihi o.o Myr Seamount 0 30 60 90 120 150 km

Explanation / Answer

1. Since both the Emperor and Hawaiian Islands Chains developed as a result of the same mantle hotspot, the possible reason that the hotspot trail changes direction at 42 Myr can be the change in the Pacific plate motion which happens approximately at the same time.

2. the from

Length of Emperor Seamount Chain = 2,300 km = 2,300 x 1,000 meters = 2,300 x 1,000 x 100 centimeters

= 230,000,000 centimeters

Time taken for the formation of Emperor Seamount Chain = 65 Myr - 42 Myr = 17 Myr = 17,000,000 yr

Therefore the rate of Pacific Plate motion relative to the Hawaiian hotspot as it was developing the 2,300 km long Emperor Seamount Chain = (230,000,000) / (17,000,000) = 13.5294 cm/yr

The direction of plate movement is north west.

3.  

Time taken for the movement = 5.1Myr - 0.8 Myr = 4.3 Myr = 4,300,000 years

Amount of movement = 9.2 centimeters on map

3.6 centimeters on map = 150 kilometers

Therefore 9.2 centimeters on map is equivalent to = (9.2/3.6) x 150 = 383.333333333 kilometers =

38,333,333.333 cm

The rate of Pacific Plate motion relative to the Hawaiian hotspot from 5.1 to 0.8 Myr, expressed in cm/year =

(38,333,333.333) / ( 4,300,000) = 8.91473 cm/year

4.

If Lo‘ihi Seamount is considered as the current location of the Hawaiian hotspot, the rate of Pacific Plate motion relative to the Hawaiian hotspot from 0.8 Myr to today, expressed in cm/yr is =

Time taken for the movement = 0.8 Myr = 800,000 years

Amount of movement = 5.5 centimeters on map

3.6 centimeters on map = 150 kilometers

Therefore 5.5 centimeters on map is equivalent to = (5.5/3.6) x 150 = 229.166666666 kilometers =

22,916,666.67 cm

If Lo‘ihi Seamount is considered as the current location of the Hawaiian hotspot, the rate of Pacific Plate motion relative to the Hawaiian hotspot from 0.8 Myr to today, expressed in cm/yr is =

(22,916,666.67) / (800,000) = 28.645833 cm/yr

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