Volcanoes are features?

Question

found on both Mars and Venus. What type of eruptions would be most common on these planets?
a. Very violent eruptions on both planets
b. Very gentle eruptions on both planets
c. Violent eruptions on Venus and gentle eruptions on Mars
d. Gentle eruptions on Venus and violent eruptions on Mars

Answer 1

C

Answer 2

I don't know the answer. But let's think about it.

Violent eruptions on earth occur because the shallow crust is brittle and the explosion occurs when volatiles like water and CO2 change from liquid to vapor (huge volume expansion blowing away the brittle crustal cover). The origin of the magma is really important too, though. Rhyolites (granitic) magma is viscous and holds more volatiles, whereas basalts are generally fluid and contain less volatiles. Granitic magmas are formed from recycled crust whereas basalts come from the mantle.

This is why mountains associated with continental margins are explosive (like Mt St Helens) but volcanoes on ocean crust are gentle (like Mauna Loa).

I do know that Mars has a huge shield (hawaii like) volcano and I am not sure that there is active plate tectonics there. Also, the absence of ocean means that any descending crust that would form volcanoes from partial melting would not be likely to be water-enriched, and thus formation of water-saturated viscous lava seems unlikely. Therefore, Gentle eruptions and not violent eruptions seem probable on Mars. However, the brittle crust and low atmospheric pressure would favor violent eruptions in the presence of water-saturated magmas, should they exist.

Venus has a hot plastic crust and I believe a higher atmospheric pressure. There also appears to be no ocean so recycling of water-rich crust is unlikely (I believe that there is little evidence for plate tectonics on venus as well). I would expect fluid eruptons both because the planet doesn't generate the appropriate magma and because the crust is not in an appropriate state for violent eruptions to be common.

But I honestly don't know.

Answer 3

I THINK C.