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.Without silica their slopes will be steep 2.The magma must not be contaminated with crustal material 3.Both 1 & 2 4.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.silicaaluminiumpotassium sodiumcalciumpolymerizedfeldsparquartz 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 1 o – 5 o Slopes for Stratovolcanoes are ~ 30 o near summit and ~10 o 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?

. 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 dating Distance is just measured Age = 60,000,000 years Distance = 5000 km. Speed = Distance/time Speed = (5 x 10 3 km)/(6 x 10 7 years) or Speed = (5 x 10 6 m)/(6 x 10 7 years) Speed = meters/year or 8.3 cm/year.

Velocity Vectors in Jules Verne Voyager Velocity vectors in Google Earth Google Earth w/ Using GPS velocity vectors to study plate motion

GSRM Model of Kreemer and Holt Observed GPS Velocities Plus Earthquake Slip directions Plate Tectonic Model with Deformable Boundaries Model Velocities and Plate Boundary Strain 5170 geodetic velocities from 86 different studies Global Plate Motions and Boundary Zones

Age from radiometric dating Distance is just measured Age = 60,000,000 years Distance = 5000 km. Speed = Distance/time Speed = (5 x 10 3 km)/(6 x 10 7 years) or Speed = (5 x 10 6 m)/(6 x 10 7 years) Speed = 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 5 o ). A chain of shield volcanoes can indicate plate tectonics is occurring.

Mons Rumker Lunar volcano Mons Rumker Lava flow

Mons Rumker – Exaggerated view Height ~ 1100 meters Diameter ~ 70 km.

Slope Measurement 1,100 m 35,000 m Angle ϴ 1,100 m 35,000 m

Which trigonometric function should you use to find the angle? 1,100 m 35,000 m Angle ϴ 1,100 m 35,000 m

The correct answer is Tangent Tan(θ) = opposite/adjacent Tan(θ) = 1100/35000 Tan(θ) = Θ = Tan -1 (0.314) Θ = 1.8 o

The correct answer is Tangent Tan(θ) = opposite/adjacent Tan(θ) = 1100/35000 Tan(θ) = Θ = Tan -1 (0.314) Θ = 1.8 o 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 = That gives θ = 3.6 o Olympus Mons is a shield volcano.

Comparison