Volcanoes

Question 1

How are volcanoes measured and when was this measurement installed?

Answer 1

Logarithmic scale called the Volcano Explosivity Index (VEI) from 0-8 formed in1982
1 = gentle
4 = cataclysmic
8 = mega colossal

Question 2

Features of an Icelandic volcano

Answer 2

Type of magma: basaltic
Characteristics: lava flows gently from fissures

Question 3

Features of a Hawaiian volcano

Answer 3

Type of magma: basaltic
Characteristics: lava flows gently from a central vent

Question 4

Features of a Strombolian volcano

Answer 4

Type of magma: thicker basaltic
Characteristics: frequent, explosive eruptions of tephra and steam. Occasional, short lava streams

Question 5

Features of a Vulcanian volcano

Answer 5

Type of magma: thicker basaltic, andesitic, rhyolitic
Characteristics: less frequent but more violent eruptions of gases, ash and tephra including lapilli

Question 6

Features of a Vesuvian volcano

Answer 6

Type of magma: thicker basaltic, andesitic, rhyolitic
Characteristics: following long periods of inactivity, very violent gas explosions blast ash high into the sky

Question 7

Features of a Peléean volcano

Answer 7

Type of magma: andesitic and rhyolitic
Characteristics: very violent eruptions of nuées ardentes

Question 8

Features of a plinian volcano

Answer 8

Type of magma: rhyolitic
Characteristics: exceptionally violent eruptions of gases, ash and pumice. Torrential rainstorms cause devastating lahars.

Question 9

What is material ejected from a volcano usually known as and what does it mean

Answer 9

Tephra - all pieces of fragments of rock ejected into the air by an erupting volcano

Question 10

What typically happens with tephra?

Answer 10

Most tephra falls back onto the slopes of the volcano, enlarging it. But, billions of smaller and lighter pieces less than 2 mm diameter (less than one tenth of an inch), termed ash, are carried by winds for thousands of miles.

Question 11

What is a plume?

Answer 11

A column of hot volcanic ash that has emitted into the atmosphere during an eruption

Question 12

What are the factors that determine the viscosity of magma?

Answer 12

Temperature, dissolved gases and chemistry

Question 13

How does temperature determine the viscosity of magma?

Answer 13

the higher the temperature, the lower the density of the magma and the more easily it will flow　

Question 14

How do dissolved gases determine the viscosity of magma?

Answer 14

the greater the amount of dissolved gases, the more fluid the magma. Gases remain dissolved in high temperature conditions.　

Question 15

How does chemistry determine the viscosity of magma?

Answer 15

the higher the silica content, the more viscous the magma.　

Question 16

What is basic magma?

Answer 16

• rich in iron, aluminium and magnesium.
• sometimes referred to as Basaltic. - It is high temperature magma (1000-1200 degrees C)
• has a high proportion of dissolved gases (4-6%)
• low silica content (44-52%).
• It is very fluid and has a low viscosity

Question 17

What is acid magma?

Answer 17

• very rich in silica (66%+).
• It is a relatively low-temperature magma (800-1000 degrees C)
• much lower proportion of dissolved gases than basic magma
• It is very thick and has a high viscosity
  There are 2 types - Andesitic and Rhyolitic magma both have a higher silica content and so have a higher viscosity. They flow less easily and often form blockages in volcanic vents. Also volcanic gases can’t escape easily from viscous lava so pressure builds up until the blockages are cleared by a violent eruption.　

Question 18

What creates more explosive eruptions

Answer 18

The more viscous the magma, the more explosive the eruption

Question 19

What types of eruptions occur at destructive boundaries?

Answer 19

As one plate is subducted below another, intense pressures and heat cause melting of the rocks and sediments, which can result in the formation of an acidic magma chamber. Very viscous and resistant to flow, there is often a huge build-up of gas which results in very violent and dangerous eruptions involving ash and pyroclastics.　

Question 20

What types of eruptions occur at constructive plate boundaries?

Answer 20

where oceanic plates are moving away from each other, the magma is produced by the partial melting of the mantle deep below the surface. It is a basic-type of magma and therefore has a low viscosity enabling it to flow easily. Volcanoes at constructive margins, for example along the Mid-Atlantic Ridge erupt frequently, but not usually violently and are associated with lava flows and ash.

Question 21

What types of eruptions occur at constructive plate boundaries - continental plates?

Answer 21

At constructive margins where continental plates are moving apart, such as the East African Rift Valley, the situation is more complex in relation to volcanic features and magma type. Often the volcanic rocks show a diversity ranging from basic to acid and there can be a variety of features from small fissure eruptions, to larger volcanoes, such as Mt Kilimanjaro.

Question 22

Where do most of the worlds volcanoes occur?

Answer 22

Whilst 75% of all volcanic material is erupted at constructive margins, most of the world’s active volcanoes (over 80%) occur at destructive margins. It is these that are generally considered to be the most hazardous.　

Question 23

Do all volcanoes occur at plate margins?

Answer 23

No - those volcanoes not directly associated with plate margins, such as those on the Hawaiian Islands, result from isolated plumes of rising magma. The magma is basic in nature and these volcanoes are similar to those associated with constructive margins.　

Question 24

What do the frequency of eruptions depend on?

Answer 24

The frequency of volcanic eruptions depends largely on their type. Kilauea, on the island of Hawaii, is an active shield volcano which has erupted basaltic lava continuously since 1983. In contrast many volcanoes that erupt rhyolitic lava, erupt very infrequently. The Yellowstone caldera has erupted 3 times in the last 2.1 million years, with an interval of between 600 000 and 800 000 years between each.

Question 25

What are fissure eruptions?

Answer 25

when 2 plates move apart, lava may be ejected through fissures rather than via a central vent. These can create extensive lava plateaus – flat, featureless basalt plains. These gentler eruptions result in large scale landscaping and are significant contributors to global climate change e.g. Heimay eruption, Iceland.

Question 26

What are basic or shield volcanoes?

Answer 26

these are typically found at constructive margins, rift valleys and hot spots. Typically lava flows out of a central vent and can spread over large areas before solidifying. The result is a cone with long, gentle sides made up of layers of lava from repeated flows. Their eruptions are gentle enough to become tourist attractions as in Hawaii and Iceland.
e.g. Mauna Loa on Hawaii.

Question 27

What are acid or dome volcanoes?

Answer 27

these are typically found at destructive margins and are steep sided convex cones associated with viscous, silica rich gaseous lava that quickly solidifies before running too far down slope. Deadly pyroclastic flows are associated with these volcanoes e.g. Mt Pelee

Question 28

What are composite cones?

Answer 28

(strato-volcanoes) are formed from alternating eruptions of tephra and lava, which builds the volcano in layers. These layers produce weaknesses that can be exploited by the magma resulting in secondary cones and fissures. e.g. Mount Etna.

Question 29

What are calderas?

Answer 29

these result when violent eruptions blow off the volcanoes summit. This empties the magma chamber and causes the sides of the volcano to collapse inwards. The resulting vast crater can be many km wide and can be flooded by the sea or fill as a lake.
e.g. Krakatoa.

Question 30

How are volcanoes monitored?

Answer 30

1. The amount of volcanic gas in the air and at ground level - this is a warning sign and can be recorded by gas sampling.
2. Remote satellite analysis and thermal imaging - this can identify changes in and round the main crater
3. Ground deformation - using tiltmeters and laser based electronic distance measurement to detect bulging of the ground caused by rising magma. Slope angles and distance between points can be measured.
4. Ground vibration is measured using seismometers and recorded using seismographs. Micro quakes indicate rising magma fracturing and cracking overlying rock.
5. Water chemistry - Rising magma will both heat groundwater and corrupt it with gases like sulphur, increasing its acidity. Rising groundwater temperature and/or gas content can be measured using hydrological equipment.

Question 31

How can scientists forecasts changes in volcanic activity?

Answer 31

Scientists collect data from the instrument networks then analyse them to look for out-of-the-ordinary signals. By comparing the data analysis with similar results from past volcanic events, volcanologists are better able to forecast changes in volcanic activity and determine whether and when a volcano might erupt in the future. These new systems are capable of collecting and transmitting accurate real-time data from the volcano back to Observatory offices, which improves eruption forecasting. It is important that instruments be installed during quiet times when volcanoes are not active so that they are ready to detect the slightest bit of volcanic stirring. Early detection gives the maximum amount of time for people to prepare for an eruption.

Question 32

How did monitoring data help with Mount St. Helens?

Answer 32

Prior to the Mount St. Helens 2004 eruption, monitoring equipment recorded a large increase in earthquake activity. Scientists quickly examined other monitoring data including gas, ground deformation, and satellite imagery to assess if magma or fluid was moving towards the surface. Based on the history of the volcano and the analysis of the monitoring data scientists were able to determine the types of magma could be moving towards the surface This type of knowledge helps scientists figure out the possible types of volcanic activity and the associated hazards to people. Knowing the hazards helps officials determine which real-time warnings are needed to prevent loss of life and property.

Question 33

What is an issue with government’s responses to scientific data?

Answer 33

Governments do not always respond to scientific predictions and disasters can result. For example, in 1985 despite warnings of an impending eruption with associated lahars, the government of Colombia failed to order an evacuation and 25,000 people lost their lives in the town of Armero when the volcano Nevado del Ruiz erupted.

Equally, Scientists do not always get it right and sometimes eruptions that seem imminent never actually occur. This reduces the scientists’ credibility in the eyes of governments and local people and can cause problems the next time an eruption seems likely.

Question 34

How is the hazard of gases associated with volcanic eruptions?

Answer 34

More than 90% of all gas emitted by volcanoes is water vapour(steam), most of which is heated ground water. Other common volcanic gases are carbon dioxide, sulphur dioxide, hydrogen sulphide, hydrogen, and fluorine. Sulphur dioxide gas can react with water droplets in the atmosphere to create acid rain, which causes corrosion and harms vegetation. Carbon dioxide is heavier than air and can be trapped in low areas in concentrations that are deadly to people and animals. Fluorine, which in high concentrations is toxic, can be adsorbed onto volcanic ash particles that later fall to the ground. The fluorine on the particles can poison livestock grazing on ash-coated grass and also contaminate domestic water supplies.

Question 35

How are lava flows or domes a hazard associated with volcanic eruptions?

Answer 35

Magma that oozes onto the Earth’s surface is called lava and forms lava flows. The higher a lava’s content of silica, the less easily it flows. For example, low-silica andesite lava can form fast-moving streams or can spread out in broad thin sheets as much as several miles wide. Since 1983, Kilauea Volcano on the Island of Hawaii has erupted basalt lava flows that have destroyed nearly 200 houses and severed the nearby coastal highway.
In contrast, flows of higher silica basalt tend to be thick and sluggish, traveling only short distances from a vent. Dacite and rhyolite lavas often squeeze out of a vent to form irregular mounds called lava domes. Between 1980 and 1986, a dacite lava dome at Mount St. Helens grew to about 1,000 feet high and 3,500 feet across.

Question 36

What are pyroclastic flows?

Answer 36

High-speed avalanches of hot ash, rock fragments, and gas can move down the sides of a volcano during explosive eruptions or when the steep side of a growing lava dome collapses and breaks apart. These pyroclastic flows can be as hot as 1,500°F and move at speeds of 100 to 150 miles per hour. Such flows tend to follow valleys and are capable of knocking down and burning everything in their paths. Lower-density pyroclastic flows, called pyroclastic surges, can easily overflow ridges hundreds of feet high.

Question 37

What are volcano landslides?

Answer 37

A landslide or debris avalanche is a rapid downhill movement of rocky material, snow, and (or) ice. Volcano landslides range in size from small movements of loose debris on the surface of a volcano to massive collapses of the entire summit or sides of a volcano. Steep volcanoes are susceptible to landslides because they are built up partly of layers of loose volcanic rock fragments. Some rocks on volcanoes have also been altered to soft, slippery clay minerals by circulating hot, acidic ground water. Landslides on volcano slopes are triggered when eruptions, heavy rainfall, or large earthquakes cause these materials to break free and move downhill.

Question 38

What are lahars?

Answer 38

Melted snow and ice as a result of the eruption combined with volcanic ash forms mud flows that can move down the course of river valleys at high speeds - 1985 a lahar destroyed the colombian town of Armero after Nevado del Ruiz eruption, only a quarter of the population survived

Question 39

How do volcanoes affect the Earth’s climate?

Answer 39

Ash - little effect on atmosphere
HOWEVER
Volcanic gases like sulphur dioxide can cause global cooling, while volcanic carbon dioxide, a greenhouse gas, has the potential to promote global warming.
The most significant climate impacts from volcanic injections into the stratosphere come from the conversion of sulphur dioxide to sulphuric acid, which condenses rapidly in the stratosphere to form fine sulphate aerosols. The aerosols increase the reflection of radiation from the Sun back into space, cooling the Earth’s lower atmosphere or troposphere.

Question 40

Does the Earth’s volcanoes emit more CO2 than humans?

Answer 40

No
Carbon dioxide is a greenhouse gas and is the primary gas blamed for climate change. While sulphur dioxide released in contemporary volcanic eruptions has occasionally caused detectable global cooling of the lower atmosphere, the carbon dioxide released in contemporary volcanic eruptions has never caused detectable global warming of the atmosphere.

Question 41

How do volcanoes create acid rain?

Answer 41

Acid rain contains a pH of less than 4 and is produced by rain water falling through volcanic emissions. The rain, with a pH between 1.5 and 3.5, has the corrosive property of battery acid. The plume cloud also contains tiny glass fragments that can irritate the eyes and, in rare cases, cause permanent damage.

Communities living close to active volcanoes may be affected by drinking acidic rainwater. It may also affect crops.

Question 42

How do volcanoes create flooding?

Answer 42

The Icelandic volcano Eyjafjallajökull exploded to life in 2010 after nearly two centuries of dormancy, spewing out a huge plume of ash that forced widespread flight cancellations for days. The volcano’s many eruptions over 10 weeks melted parts of the volcano’s icecap, generating more than 140 of the floods.

Question 43

How do volcanoes create tsunamis?

Answer 43

Sea waves generated by violent volcanic eruptions such as those formed after the eruption of Krakatoa in 1883.