Lesson2d Volcanoes. Olympus Mons (volcano on Mars) compared to Arizona.

Lesson2d

Volcanoes

Olympus Mons (volcano on Mars) compared to Arizona

Olympus Mons on Mars

• Google Mars• Mars Reconnaissance orbiter – HiRISE• Basal Scarp on Olympus Mons

Hawaiian Islands

Mt. Saint Helens – May 18, 1980

• The lava from the Hawaiian volcanoes is very low in silica and it flows easily across the surface, all the way to the ocean.

• What can you conclude about the Hawaiian volcanoes?

.

1 2 3 4

0% 0%0%0%

1. Without silica their slopes will be steep

2. The magma must not be contaminated with crustal material

3. Both 1 & 24. None of the above

Lava Composition• Felsic lava (Strato-volcanoes) -- high viscosity and

strength, high in silica, aluminium, potassium, sodium, and calcium, forming a polymerized liquid rich in feldspar and quartz.

• Mafic or basaltic lavas (Shield volcanoes) are typified by their high ferromagnesian content, Basaltic magma is high in iron and magnesium, and has relatively lower aluminium and silica. This is mantle material.

• Note: Similar to the lava in the Mid-atlantic ridge.

Mt. Rainer overlooking Tacoma

Shield volcanoes

• Shield volcanoes get their appearance because the low viscosity lava flows out and spreads easily.

• Slopes for Shield volcanoes are around 1o – 5o

• Slopes for Stratovolcanoes are ~ 30o near summit and ~10o on outer slopes.

Shield volcanoes arise from mantle magma plumes.

Hot magma from near the core of the Earth rises in a plume.

Detailed model of plume rise.Slow process, last slide is 76.8 Million years.

Oldest Island

Youngest Island

Oldest

Youngest

Increasing age

Evidence.• Magma plumes take many millions of years to

form and rise up through the mantle.• The Big Island is the only one to have active

volcanoes today.• The farther away in the chain of islands you

get the older the island is.

• Given all this information, how did the Hawaiian Island chain form?

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1 2 3

0% 0%0%

1. From magma coming from a Pacific ridge similar to the mid-Atlantic ridge

2. From the wandering of the magma plume under the sea floor

3. From the motion of the Pacific Oceanic Plate over the magma plume.

Ocean plate motion relative to the mantle plume (Plate Tectonics)

How can we determine how fast the Pacific plate moving?

Age from radiometric datingDistance is just measured

• Age = 60,000,000 years• Distance = 5000 km.• Speed = Distance/time • Speed = (5 x 103 km)/(6 x 107 years) or• Speed = (5 x 106 m)/(6 x 107 years)• Speed = 0.083 meters/year or 8.3 cm/year.

Velocity Vectors in Jules Verne Voyager Velocity vectors in Google Earth

http://jules.unavco.org/VoyagerJr/EarthScope Google Earth w/http://pboweb.unavco.org/products/velocity/pbo_final_frame.kmzhttp://facility.unavco.org/data/maps/maps.html

Using GPS velocity vectors to study plate motion

GSRM Model of Kreemer and Holt

Observed GPS Velocities

Plus Earthquake Slip directions

Plate TectonicModel with DeformableBoundaries Model Velocities and Plate

Boundary Strain5170 geodetic velocities from 86 different studies

Global Plate Motions and Boundary Zones

Age from radiometric datingDistance is just measured

• Age = 60,000,000 years• Distance = 5000 km.• Speed = Distance/time • Speed = (5 x 103 km)/(6 x 107 years) or• Speed = (5 x 106 m)/(6 x 107 years)• Speed = 0.083 meters/year or 8.3 cm/year.

• Geodetic measurement of plate motion is 10.3 to 11.8 cm/year

Results we can use

• A shield volcano arises from a deep mantle plume.

• Shield volcanoes have gentle slopes (less than 5o).

• A chain of shield volcanoes can indicate plate tectonics is occurring.

Mons Rumker

Lunar volcano

Mons Rumker

Lava flow

Mons Rumker – Exaggerated viewHeight ~ 1100 meters

Diameter ~ 70 km.

Slope Measurement

1,100 m

35,000 m

Angle ϴ

Angle ϴ1,100 m

35,000 m

Which trigonometric function should you use to find the angle?

1,100 m

35,000 m

Angle ϴ

Angle ϴ1,100 m

35,000 m

• The correct answer is Tangent

• Tan(θ) = opposite/adjacent• Tan(θ) = 1100/35000• Tan(θ) = 0.314• Θ = Tan-1(0.314)• Θ = 1.8o

• The correct answer is Tangent

• Tan(θ) = opposite/adjacent• Tan(θ) = 1100/35000• Tan(θ) = 0.314• Θ = Tan-1(0.314)• Θ = 1.8o

Mons Rumker is a shield volcano

Olympus Mons – Largest volcano on Mars (and entire solar system)

Olympus Mons compared to Arizona

Topographical map of Mars

Olympus Mons

Estimate the ratio

of the opposite

to adjacent

sides

• Using the ratio of 20km/320km = 0.0625

That gives θ = 3.6o

Olympus Mons is a shield volcano.

Comparison