Earth Science

Geological Activity from Plate Tectonics Processes

Volcanic Eruptions

Study Tip
Even dormant or inactive volcanoes are under observation and monitoring. For instance, a supervolcano at Yellowstone Park that is currently dormant erupts every several million years.

Predicting Volcanic Eruptions

Evidence from a volcano’s history, earthquakes, slope deformation, and gas emissions can help predict future volcanic eruptions. Observation satellites are sometimes used to monitor changes in gas, temperature, and formations at volcanic sites.

History of Volcanic Activity

  • The time span between last eruption and previous eruptions are monitored. Earthquakes
  • The number and size of earthquakes increases before an eruption due to moving magma
  • Scientists use seismographs that record the strength and duration of an earthquake to determine whether or not a eruption will occur in the near future

Gas Emissions

  • Sulfur dioxide, carbon dioxide, hydrochloric acid, and water vapor are several gasses that can be measured at volcanic sites
  • The amounts of gases and their ratios are calculated to predict eruptions
Study Tip
Study Tip
The same way a person may cast a shadow over another person when they stand under the sun, planets or celestial bodies that have aligned themselves cast shadows over one another as well.
Even dormant or inactive volcanoes are under observation and monitoring. For instance, a supervolcano at Yellowstone Park that is currently dormant erupts every several million years.
Small pyroclastic flow at Mayon volcano in the Philippines
Small pyroclastic flow at Mayon volcano in the Philippines

Explosive Eruptions

Explosive eruptions are caused by gas-rich magma that churns within the magma chamber. This churning creates pressure, which can overwhelm and break through the rock that encases it.

Volcanic Material
Description
Tephra
The erupted rock fragments
Pyroclastic flow
Scorching hot tephra, ash, and gas
Lahar
Volcanic mudflow containing ash, rock, and water
Poisonous gasses
These gasses contribute to acid rain and ozone destruction

Effusive Eruptions

Effusive eruptions are caused by mafic magma buildup. Although the pressure builds enough for the magma to erupt, it does not erupt with the same force as felsic magma. The magma pushes toward the surface through fissures.

Earth Science

Type of lava flow
Description
A’a
Forms a thick and brittle crust that is torn into rough pieces.
Pāhoehoe
Forms lava tubes where fluid lava flows through the outer cooled rock crust. Smooth and ropy look
Pillow lava
Mafic lava that erupts underwater. The lava cools very quickly and forms roughly spherical rocks
Type of lava flow
(a) A’a lava  (b) Pāhoehoe lava tubes   (c) Pāhoehoe lava  (d) Pillow lava
Concept Check
  • What kinds of evidence can scientists use to predict volcanic eruptions
  • What causes an explosive eruption?
  • What is pyroclastic flow?
  • What causes an effusive eruption?
  • What are three types of lava that flow from effusive eruptions?