Weather & Climate : Tectonic Events and Volcanic Activity

Tectonic Events and Volcanic Activity

Introduction:

Many processes can cause climate change. These processes include variations in the amount of energy the Sun produces over the years; the positions of the continents over millions of years; the amount of tilt in the Earth’s axis; variations in Earth’s orbit over thousands of years; the impact of asteroids on Earth; variations in the greenhouse gases in the atmosphere. Some of these processes are caused naturally, and some by human activities.

Plate tectonics is a theory that states that the lithosphere, the Earth’s solid outer crust, is separated into plates. These plates move over the molten upper portion of the mantle (asthenosphere).

The plates interact in three ways: 

1.  The movement of plates away from each other is called divergent boundaries (also called spreading centers); 
2. The movement of plates towards each other is called convergent boundaries. Convergent boundaries are where continents collide and create mountain ranges or one plate falls below another plate at subduction zones and produces volcanic arcs;
3. Plates slip over each other at transform boundaries creating strike-slip faults.

The uplift and falling of land, the sudden release of energy that causes shaking(earthquakes), and volcanic eruptions are all indications of interactions and stress caused due to the movement of the plates. The movement of plates may seem slow, but over millions of years, plate tectonics form the distribution of continents, oceans, and mountain ranges that form different ecosystems, affecting global climate.

The movement of plate tectonic can cause changes in the climate. Over millions of years, ocean currents may circulate heat differently as seas open and close. For example, when all the continents are merged into one supercontinent (such as Pangaea), almost all places experience a continental climate. When the continents divide, heat is uniformly scattered.

The movements of plate tectonic may help to start an ice age. When continents are situated near the poles, ice accumulation can occur, which may increase albedo (a unitless quantity that shows how well a surface reflects sun energy) and decrease global temperature. Adequate low temperatures may start a global ice age.

When tectonic plates move on geological timescales, land masses are taken to various locations and latitudes. These variations cause global circulation patterns of air and ocean water and the climate of the continents. One type of proof for plate tectonics and an example of how plate tectonics affects the environment is the site of coal mines.

Coal mines were formed millions of years ago in tropical areas, but today they are found at higher latitudes. Since the industrial revolution, the Northern Hemisphere has warmed up more than the Southern Hemisphere. This happens because the Northern Hemisphere has a more significant percentage of Earth’s landmass as compared to the ocean than the Southern Hemisphere. We know that landmasses warm faster than oceans because of the high heat capacity of the oceans.

Movements of the plate (when two plates come together)cause volcanic eruptions, which circulate dust and CO₂ into the atmosphere. CO₂ can cause global warming. Vast eruptions of the lava produce more gas and dust and can alter the climate for many years. Such a type of volcanic eruption is extremely rare.

Volcanic Eruptions

Volcanic eruptions release molten rock, or lava, from deep within the Earth; on cooling, lava forms new rock on the Earth’s surface. But these volcanic eruptions also affect the atmosphere.

During volcanic eruptions, the gases and dust particles thrown into the atmosphere impact the climate. Most of the particles gushed from volcanoes cool the Earth by blocking some percentage of incoming solar radiation.

Depending on the characteristics of the eruption, volcanoes also caused global warming over millions of years during times in Earth’s history when excessive amounts of volcanic eruptions occurred, releasing greenhouse gases into the atmosphere.

Volcanic eruptions release carbon dioxide but can also release aerosols, such as volcanic ash or dust, and sulfur dioxide gas. Aerosols are liquids and solids that float all around in the air.

They may also contain soot, dust particles, salt crystals, bacteria, and viruses. Aerosols spread incoming solar radiation that causes a slight cooling effect. Volcanic aerosols can prevent some percentage of sunlight and cause a cooling that cooling effect can go on for 1-2 years.

In violent volcanic eruptions, ash, and sulfur dioxide (SO₂) gas particles are emitted into the stratosphere. After a few days, the larger particles settle, whereas the sulfur dioxide gas combines with water vapor to form sulfuric acid (H₂SO₄) and sulfate particles. These are collectively known as sulfurous aerosols.

These sulfurous aerosols are transported by wind around the Earth in easterly or westerly directions. Hence, volcanoes that erupt at lower latitudes, i.e., closer to the equator, are more likely to affect hemispheric or global cooling. Volcanoes that erupt at higher latitudes, i.e., closer to the poles, have less chance to cause cooling because the sulfurous aerosols are limited to wind patterns surrounding the poles.