Earthquakes and Volcanoes – the essentials! · boundary are violent earthquakes and fold mountains such as in the Andes Mts. ... plates is pushed upwards to form mountains such

Earthquakes and Volcanoes – the essentials!

You will need to know about the Earth’s tectonic plates (plate names and locations, direction of plate

movement and types of plate boundaries):-

Destructive Plate Boundary This is where a continental and oceanic plate are moving towards each other. As they meet the oceanic is forced down where it melts in the subduction zone. The molten rock rises through cracks in the rock and and creates a composite volcano. Other features of the destructive plate boundary are violent earthquakes and fold mountains such as in the Andes Mts.

Constructive Plate Boundary This is where two plates diverge and pull apart. As a gap appears between the two plates, lava can escape in a line or fissure. The lava creates new oceanic crust and forms mid-ocean ridges such as the one that runs down the centre of the Atlantic Ocean. Volcanoes can be found in certain locations but they are more gentle than at destructive plate boundaries. Mild or gentle earthquakes also occur. Iceland is the result of this type of plate boundary.

Conservative Plate Boundaries At these boundaries two plates slide past each other as in the case below. In fact both are moving in the same direction but as the Pacific Plate is moving faster, it gives the impression that they are moving in different directions. Severe earthquakes occur at this type of plate boundary.

Collision Plate Boundary These occur when two plates are converging but are both continental plates. As continental plates cannot be destroyed, the land between the two plates is pushed upwards to form mountains such as the Himalayas. Only earthquakes take place here as there are no volcanoes.

The CE examiners will expect you to know that there is a strong connection between the Earth’s volcanoes/earthquakes and plate boundaries. They might ask you to describe and explain the distribution on a map:-

You also need to know how to annotate a diagram showing what happens at a DESTRUCTIVE plate boundary:-

You will need to revise an example of both an earthquake and a volcano to show the nature, causes, environmental and human effects, and human responses. The question could focus on either or a combination of both.

Case Study of a Volcanic eruption in a MEDC – 1980

eruption of Mount St. Helens in 1980

Where is Mount St. Helens?

Mount St. Helens is part of the Cascade Mountain range found in the state of Washington, north west USA. Make sure you are able to locate the volcano on a world map!

What caused the volcano to erupt in 1980?

Mount St. Helens lies on the boundary between two plates, the relatively small Juan de Fuca plate and the large North American plate. Over many thousands of years the oceanic crust of the Juan de Fuca plate has been moving eastwards towards the continental North American plate. The oceanic plate has been forced downwards. This movement has caused friction which produces earthquakes and, due to an increase in temperature, destroys the oceanic plate. Molten lava has moved up through cracks in the edge of the continental plate, creating a line of volcanoes called the Cascade Mountains.

Impacts on the environment Impacts on the people Earthquake caused landslide of rock, glacier ice and soil to fill Spirit lake. Water displaced from the lake flooded the Toutle Valley and and sediment blocked the port of Portland. Side of mountain blown northwards – every plant and animal destroyed. Mountain reduced in size by 390 meters. Ash, sediment and mud raised temperature of the water in lakes and rivers, killing all fish. Every tree lying 25 km to the north was flattened. Within days the ash had completely circled the world.

25km exclusion zone set up before eruption. Sixty one deaths reported, most by poisonous gases. Logging camps destroyed – economy suffered. Several roads and railways washed away – disruption to travel. Electricity supplies interrupted and telephone wires cut. People in town of Yakima had to wear masks to protect against the heavy ash. 12% of farming crop ruined by dust settling Tourism affected.

Responses to the 1980 eruption:-

Official warnings and media reports caused most people to evacuate to a save place.

An area of 25 square miles around the volcano was designated a Red Zone – people were not allowed in without permission.

Because there was little activity in the couple of days prior to the eruption, people were allowed back in to collect their belongings – some stayed and perished.

People in the nearby town of Yakima wore masks to prevent lung damage from the ash.

10 million trees were planted to help the logging business recover.

Mount St. Helens National Monument set up – this covered 110,000 acres around the volcano to accommodate the increasing number of visitors coming to the area. Tourism grew – people wanted to see the aftermath of the volcano.

1.8 million meter square of ash was cleared from highways and airports in Washington State.

$951 million disaster relief allocated to rebuilding the area.

Scientists at the Cascades Volcano Observatory continually monitor activity and assess the hazards posed by the region’s volcanoes.

Case Study of an Earthquake event in an LEDC – The Nepal

Earthquake of 2015

What happened? Nepal is one of the poorest countries in the World (an LEDC). The earthquake

occured at 11:26 (local time) on Saturday 25th April 2015; estimated at 7.9 on the Richter Scale.

Aftershocks followed (one at 7.3 on the scale). Main quake approx. 80 km to north west of

Kathmandu, the capital.

Causes of the earthquake - The quake occurred due to ‘thrust faulting’ near the Collision Boundary

between the Eurasian Plate and the Indian Plate. The Indian Plate is colliding with Eurasia at a rate of

45mm per year, causing the uplift of the Himalayan mountain range.

Environmental Impacts Economic Impacts Social Impacts 8,632 dead (Official death toll)

19,009 injured (Official)

Worst earthquake in Nepal in

more than 80 years

Temperatures dip in Nepal at

night, and people chose to sleep

outside due to aftershocks or

houses collapsing

Hundreds of thousands of people

were made homeless with entire

villages flattened

1.7 million children had been

driven out into the open

Centuries-old buildings were

destroyed at UNESCO World

Heritage sites in the Kathmandu

Valley, including some at the

Changu Narayan Temple and the

Dharahara Tower.

Thousands of houses were

destroyed across many districts of

the country

Harvests reduced or lost this

season

U.S. Geological Survey initially

estimated economic losses at 9

percent to 50 percent of gross

domestic product, with a best

guess of 35 percent.

Short term loss of tourist revenue,

a major industry in Nepal, is

expected

The earthquake triggered

avalanche on Mount Everest,

killing 17 people. Estimates put the

number of trekkers and climbers at

base camp at the time of the

quake at up to 1000

The steep valleys of the area

suffered many landslides, the

village of Ghodatabela was

covered killing 250 people

Case Study of an Earthquake event in an MEDC – The

Japanese earthquake and tsunami of 2011

What happened? There was a magnitude 7.2 earthquake on the 9th of March, 2011, 2 days before

the 8.9-9.0 magnitude earthquake of the 11th. There were also huge numbers of large sized

aftershocks, as big as magnitude 6. The epicentre was 30 kilometres below the Pacific Ocean seabed and 129 km off the east coast of Honshu, Japan. This triggered a tsunami. High, powerful waves were generated and travelled across the Pacific Ocean. The area worst affected by the tsunami was the east coast of Honshu in Japan.

Causes of the earthquake and resulting tsunami - Japan is located at the meeting point of 3 tectonic

plates, The Eurasian, Pacific and Philippines. The boundary is to the East of the 4 main Japanese

islands, Hokkaido, Honshu, Shikoku and Kyushu. It is a convergent DESTRUCTIVE boundary, with

faults running off the boundary. In effect, Japan owes its existence to this boundary and the Islands

are volcanic in origin. Japan gets 30% of the world’s earthquakes every year, and there is 90mm of

movement of the Pacific Plate under the Eurasian.

The reason why the Tōhoku Earthquake happened was due to the build up in strain energy as the

Pacific plate subducted under the Eurasian plate. This strain energy eventually overcame the

frictional force holding the plates in place, and was released as earthquake waves.

The tsunami is a secondary consequence of this initial movement. The Eurasian plate was down

warped (dragged down) as the Pacific plate descended. When the strain energy was released this

section of the Eurasian plate “popped” or bounced back upwards. This displaced the water above in

the Pacific Ocean causing a Tsunami wave to ripple radially outwards. This was known as a

megathrust earthquake.

The aftershocks occurred as the strain energy was passed along the fault, causing further quakes.