Exercise NO. 3 Read the passage then answer the questions based on Figure 1below

Question

Exercise NO. 3

Read the passage then answer the questions based on Figure 1below and your knowledge of plate tectonics.

On the night of November 13, 1985, Nevado del Ruiz, a 16, 200 foot snowcapped volcano in NW Colombia erupted. Snow melted, sending a wall of mud and water raging through towns as far as 50 kilometers away, and killing 25,000 people. Long before the disaster struck, Nevado del Ruiz was marked as a trouble spot. Like Mexico City, where an earthquake killed atleast 7,000 people in October 1985, Nevado del Ruiz is located along the Ring of Fire. This ring of islands and the coastal lands along the edge of the Pacific Ocean are prone of volcanic eruptions and crustal movements.

The ring gets its turbulent characteristics from the motion of the tectonic plates under it. The perimeter of the Pacific, unlike that of the Atlantic is located above tectonic plates. Nevado del Ruiz happens to be located near the junction of four plate boundaries. In this area an enormous amount of heat is created, which melts the rock 100 to 200 kilometers below Earth’s surface and creates magma.

Nevado del Ruiz had not had a major eruption for 400 years before this tragedy. The reason: sluggish magma. Unlike runny, mafic magma that makes up the lava flow of oceanic volcanoes such as those in Hawaii, the magma at this type of subduction plate boundary tend to be sticky and slow moving, forming the rock andesite when it cools. This andesitic magma tends to plug up the opening of the volcano. It sits in a magma chamberunderground with pressure continually building up. Suddenly, tiny cracks develop in Earth’s crust, causing pressure to drop. This causes steam and other gases dissolved in the magma to violently expand, blowing the magma plug free. Huge amounts of ash and debris are sent flying, creating what is called an explosive eruption.

Oddly enough, the actual eruption of Nevado del Ruiz did not cause most of the destruction. It was caused not by lava but by the towering walls of sliding mud created when large chucks of hot ash and pumice mixed with melted snow.

1. What are the names of the four tectonic plates located near the Nevado del Ruiz volcano? (5)

2. What caused most of the destruction associated with the eruption of the volcano? (5)

3. What caused the magma to expand, blowing the magma plug free? (5)

4. Vesicular texture is very common in igneous rocks formed during andeisitc eruptions. Explain how this texture is formed. (5)

5. Why are eruptions of Nevado del Ruiz generally more explosive than most Hawaiian volcanic eruptions? (5)

6. Describe one emergency preparation that may reduce the loss of live from a future eruption of the Nevado del Ruiz Volcano. (5)

Explanation / Answer

1. Nazca Plate, South American Continental Plate, Cocos and Caribbean plates are four tectonic plates located near the Nevado del Ruiz volcano.

2. Most of the destruction associated with the eruption of the volcano by the towering walls of sliding mud created when large chucks of hot ash and pumice mixed with melted snow.

3. The andesitic magma tends to plug up the opening of the volcano. It sits in a magma chamberunderground with pressure continually building up. Suddenly, tiny cracks develop in Earth’s crust, causing pressure to drop. This causes steam and other gases dissolved in the magma to violently expand, blowing the magma plug free.

4. Vesicular texture is the texture in which the rock being pitted with many cavities at its surface and inside and there cavities are known as vesicles and thus this texture is known as Vesicular texture. This texture forms when this gasses present in the magma are able to come out of solution and this forms gas bubbles or the cavities inside it. When the magma finally reaches the surface as lava and cools, the rock solidifies around the gas bubbles and traps them inside, preserving them as holes filled with gas called vesicles.

5. The eruptions of Nevado del Ruiz generally more explosive than most Hawaiian volcanic eruptions because of the sluggish magma present inside the Nevado del Ruiz which causes steam and other gases dissolved in the magma to violently expand, blowing the magma plug free. Huge amounts of ash and debris are sent flying, creating what is called an explosive eruption.

6. System to bifurcate the towering walls of sliding mud created when large chucks of hot ash and pumice mixed with melted snow to some inhabited area should be done so that to reduce the loss of live from a future eruption of the Nevado del Ruiz Volcano.

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