Volcanic Activity and Earth's Plate Movements
Overview of Volcanic Activity Control by Earth's Plates
The movements of the Earth's tectonic plates have a significant impact on volcanic activity.
Continental Rift Volcanism
Definition: Continental rift volcanism occurs in areas where tectonic forces cause the Earth's plates to stretch, usually on continents.
Key Features:
Formation of a rift valley:
The Earth's crust is pulled apart, causing it to sink, forming a valley.
Example locations include the East African Rift Valley and parts of the Western United States (e.g., Nevada).
Formation of cracks in the crust which allow magma to rise from the mantle.
Mechanism:
As tectonic plates separate, the mantle underneath is depressurized (less weight on top).
This reduction in pressure enables the hot mantle rock to melt, forming magma which leads to the creation of volcanoes.
Subduction-Related Volcanism
Key Concept: More significant volcanic activity is correlated with the process of subduction where one tectonic plate moves under another.
Types of Subduction:
Oceanic-Continental Subduction:
Ocean floor subducts beneath a continental plate, resulting in the formation of an ocean trench.
At approximately 80 miles depth, the subduction process triggers melting of the mantle, causing magma to rise.
This results in a series of volcanoes along the continent, forming a CONTINENTAL VOLCANIC ARC.
Example: The Andes Mountains, which illustrate this process.
Oceanic-Oceanic Subduction:
Involves the subduction of one oceanic plate underneath another.
Similar magma generation occurs, causing the formation of volcanic islands.
Resulting volcanic formations occur in the ocean and are referred to as VOLCANIC ISLAND ARCS.
Examples: The Aleutian Islands, Philippines, and Marianas Islands.
Hot Spot Volcanism
Definition: Hot spot volcanism refers to volcanic activity that occurs from localized areas where magma is generated.
Formation Mechanism:
Hot spots are created by mantle plumes, which are large columns of hot magma rising from deep in the Earth's mantle.
It is theorized that these mantle plumes may remain stationary as tectonic plates move over them.
Volcanic Formation Process:
As tectonic plates migrate over a mantle plume, volcanoes form at the site of the plume.
The formed volcano can become inactive as the plate continues to move, allowing another volcano to form in succession.
This process results in a chain of volcanic islands.
Example: The Hawaiian Islands are a result of this process, forming sequentially over a stationary hot spot as the Pacific Plate moves.
Summary of Volcanism Mechanisms
Volcanic activity on Earth can be attributed to:
Continental rift volcanism (stretching of the plates leading to rift valleys).
Subduction processes (oceanic-continental or oceanic-oceanic), forming volcanic arcs.
Hot spots producing chains of volcanic islands when tectonic plates interact with stationary mantle plumes.