Types of Volcano & Eruption

Question 1

What is a Fissure volcano?

Answer 1

An open fissure, wherein basaltic lava flows a considerable distance over gentle slops. They result from lava being ejected through tense, linear fissures at constructive margins.

Question 2

What is a Shield volcano?

Answer 2

It has gently sloping sides built up by numerous flows. An example of this is Mauna Kea in Hawaii, formed by basaltic lava pouring out in huge quantities. It spreads and solidifies over a wide area, with a low viscosity due to <50% silica content. It can erupt at 1200 degrees.

Question 3

What is a Composite Cone volcano?

Answer 3

A crater volcano with a parasitic cone. It is formed on destructive boundaries from alternating lava layers. It is largely acidic, with >50% silica at 800 degrees so it flows slower. Mt Etna is a cone, with a 50 degree slope at base, 30 at summit and marked crater.

Question 4

What is an Acid Volcano?

Answer 4

Steep convex sides with a spine out the magma shaft. Forms when acid lava solidifies on exposure to air, blocking the main vent. These are steep-sided and jut straight out.

Question 5

What is an Ash Volcano?

Answer 5

When ash and cinder build up in a small cone in layers - it is highly permeable and can only be up to 800m high, any further and it collapses in on itself.

Question 6

What is a Caldera Volcano?

Answer 6

Earth subsistence causes it to collapse in on itself, creating an opening several km wide. This often fills with rainwater, from which a secondary cone can form in the middle of the lake - Wizard island in Crater Lake, Oregon.

Question 7

What is an Icelandic eruption?

Answer 7

Effusive - lava flows out from fissure.

Question 8

What is a Hawaiian eruption?

Answer 8

Effusive - lava emitted gently from vent

Question 9

What is a Strombolian eruption?

Answer 9

Effusive - small but frequent

Question 10

What is a Vesuvius eruption?

Answer 10

Singular violent eruption after a long period of inactivity.

Question 11

What is a Krakatoan eruption?

Answer 11

Exceptionally violent eruption.

Question 12

Why is a Plinian eruption?

Answer 12

Large mounds of lava and pyroclast.

Question 13

What is a Pahlean eruption?

Answer 13

Lava seeps laterally out the sides, with pyroclastic flow.

Question 14

How does the chemical composition of lava depend on geology?

Answer 14

Basaltic lavas form from the melting of ocean crust, whereas rhyolitic lazes with high silica content form from melting of continental crust.

Question 15

What are the 3 situations in which volcanoes form?

Answer 15

Diverging margins, Converging margins and hotspots.

Question 16

How are volcanoes produced from Diverging margins?

Answer 16

75% of Earth’s magma comes from these.
Mainly mid-ocean where upper mantle eating produced basaltic magma.
Non-violent and non-major hazards, except where they cross inhabited islands (Iceland)

Question 17

How are volcanoes produced from Converging margins?

Answer 17

80% of volcanoes form here.
As the oceanic plate subjects and melts, magma rises and mixes with a continental plate. Can cause violent volcanic activity.

Question 18

How are volcanoes produced from hotspots?

Answer 18

Hawaiian islands have effusive eruptions with huge quantities of low-viscosity magma. Less hazardous as it can cause considerable damage.