Volcanism and Volcanic hazards

Question 1

The term volcano came from the name of ______, the Roman god of fire and metal working.

Answer 1

Vulcan

Question 2

geologic landform where molten rocks, gases and pyroclastic debris erupt through the earth’s crust or has done so within the past several million years.

Answer 2

volcano

Question 3

true or false

Volcanoes vary in morphology (shape, size) and eruption styles.

Answer 3

true

Question 4

Different factors that may affect why a volcanic eruption is triggered.

Answer 4

(1) the influx of new magma supply from a deeper source (possibly a bigger magma chamber),
(2) melting of surrounding country rocks,
(3) exsolution of gasses (vesiculation and degassing) during the ascent of the magma to the surface, and /or
(4) sudden contact with water.

Question 5

magma is formed in three tectonic settings:

Answer 5

(1) divergent boundaries or spreading centers (decompression melting) such as the Mid-Atlantic ridge,
(2) convergent boundaries (flux melting) such as the Pacific ring of fire, and
(3) mantle plumes/ hotspots (decompression melting and usually hot temperature) that may occur as intraplate volcanism such as in Hawaii

Question 6

Where are most volcanoes found?

Answer 6

most volcanoes are found very close to the edges of the plates.

Question 7

Where much of magma is stored

Answer 7

Magma chamber

differs in size, shape, depth and many other characteristics.

Question 8

Can a volcano be connected to more than one magma chamber

Answer 8

yes

or a small magma chamber at shallower depth is further connected to a larger magma chamber at depth.

Question 9

During an increased period of volcanic activity, the magma migrates upward from the magma chamber into the

Answer 9

Vent or a conduit

Question 10

In ideal cases, the magma would flow out into a small (<1 km) circular depression usually at the summit called

Answer 10

crater

following the central vent.

Question 11

in some cases, the magma may emerge in secondary sites away from the main crater and in other conduits such as those found at the side of the volcano resulting in a

Answer 11

flank eruption

Question 12

the largest among all volcanoes.

It is made up of thin (up to tens of meters thick) but successive basaltic lava flows

Very little pyroclastic materials may be present, and most are concentrated in the vent where lava fountaining occurs.

usually associated with hotspots and mantle plume sources that can generate continuous and voluminous supply of magma

Answer 12

Shield Volcano

It has a roughly circular or oval shape in map view and is similar to a roman shield lying in the ground where its name was derived.

Examples of this volcano type include Mauna Kea and Mauna Loa both in Hawaii.

Question 13

true or false

the general slope of a shield volcano is generally gentle (15o or less) especially close to the summit.

Answer 13

true

Owing to its fluidity, the lavas can have high velocities allowing them to spread tens of kilometers away from its source.

This is also the reason why the general slope of a shield volcano is generally gentle (15o or less) especially close to the summit.

Question 14

• are relatively small (usually <300 m high).
• These volcanoes are usually made of ejected pyroclastic deposits (usually ash and scoria) from mildly explosive eruptions.

have very steep slopes (30 – 40o) due to the stacking of pyroclastic products as determined by the angle of repose.

Internal layered structure forms due to varying intensities of the explosions that deposit different sizes of pyroclastics.

may also form close to the summit vent and flank vents of stratovolcanoes.

Answer 14

Cinder cones

• Lava flows may also be emitted by these volcanoes in the later stages of eruption and usually in a side vent at the flank.
• An example of a well-studied cone is the Paricutin volcano in Mexico which erupted for 9 years since 1943.

A local example is the Taal volcano (complex type with multiples cones).

Question 15

• have the most majestic shape among the different volcano types – the iconic near conical shape for volcanoes.

It also has relatively steeper slopes compared to shield volcanoes - around 6 to 10° low on the flanks to 30° near the top

made up of alternating tephra and lava flows ranging from andesitic to rhyolitic composition.

Answer 15

Composite/Stratovolcanoes

known for their violent eruption making this type of volcano particularly dangerous.

This type of volcano is common in subduction zone settings as depicted in figure 6. Mt. Fuji in Japan and

Mt. Mayon in the Philippines are some of the well-known stratovolcanoes.

Question 16

are roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano.

Answer 16

Lava domes

○ A well known example of a dome is the composite dome which formed from 1980 to 1986 at the crater of Mt. St. Helens in the United States.

Question 17

circular to elliptical large depressions with diameters ranging from 1 km to 50 km

It forms as a result of collapse of a volcanic structure.

Due to the weight of the overlying volcanic structure, parts of the volcano will collapse to fill in the gap left by the erupted magma forming this

Answer 17

Calderas

○ In the Philippines, an example of this is the Taal caldera.
- The Taal volcanic island is just part of the greater Taal caldera (includes the Taal lake) that encompasses several municipalities in the province of Batangas and Cavite (Tagaytay ridge).

Question 18

○ A well-known example of caldera is _______ which formed upon the eruption of the Mt. Mazama and Anak Krakatau in Indonesia which was spawned from the original Krakatau volcano.

Answer 18

Crater lake Oregon

Question 19

Baretto et al. (2019), also discovered possibly the biggest caldera by far in the planet. This was named as

Answer 19

the Apolaki caldera (150 km diameter - twice the size of Yellowstone caldera) found in the Benham rise in the offshore east of Luzon island

Question 20

○ linear, elongated fractures where very fluid, basaltic lavas erupt.

Lava fountains and lava curtains may be created in these fractures and may last for a few hours or days.

Answer 20

Fissures

○ Fissures are common in Icelandic and Hawaiian volcanoes.

Question 21

The June 15, 1991 Pinatubo eruption reached a VEI

Answer 21

VEI of 6

Question 22

The largest eruption only reached up to VEI of

Answer 22

VEI of 8

Taupo Volcano, Yellowstone

Question 23

magmas that are typically associated with non-explosive eruptions due to low viscosities and low gas contents,

Answer 23

basaltic-to-andesitic magmas

Question 24

magmas produce explosive eruptions due to the high viscosities and high gas contents.

Answer 24

andesitic-to-rhyolitic magmas

Question 25

true or false Highly degassed felsic magmas may erupt at the surface non-explosively (as viscous lava domes or obsidian flows

Answer 25

true

Question 26

true or false when very hot basaltic magmas suddenly interact with water (groundwater or surface water in most cases), thermal contraction may occur triggering violent explosive (hydrovolcanic) eruptions.

Answer 26

true

Question 27

magma rises through the surface and flows out of the volcano as a fluid material called lava. Gases can escape easily in this scenario.

Answer 27

EFFUSIVE TYPE (Non-explosive)

Question 28

magma is torn apart as it rises and reaches the surface into pieces known as pyroclasts. dissolved gases in the magma cannot escape as easily which leads to pressure build up and eventually leading to a violent eruption episode

Answer 28

EXPLOSIVE TYPE

Question 29

- characterized by the effusive emission of highly fluid basaltic lavas with low gas contents. - Steady lava fountaining (may last for days) and the production of thin lava flows are some of the most distinct characteristic of this eruption. It is generally a non-explosive eruption type.

Answer 29

Hawaiian

Question 30

- Intermittent, episodic, and short-lived (a few minutes to a few hours), explosive outbursts of pasty (partially molten) lava sometimes accompanied by booming blasts as the usual descriptions for this eruption No sustained eruption column (cloud of eruption) is produced.

Answer 30

Strombolian The 1968 and 1969 eruption of Taal along with a short episode in January 13, 2020 are examples of local strombolian eruptions.

Question 31

large quantity of pyroclastic materials is blown out of a central crater, fall back (instead of rising into a cloud), and form tongue-like, glowing avalanches (can be clearly visible at night)

Answer 31

Pelean The 1948-1953 Hibok-hibok eruption in Camiguin belongs to this type.

Question 32

tongue-like, glowing avalanches

Answer 32

nuee ardantes

Question 33

- caused by vaporization of surface/ground waters with no magma-water contact. - This eruption is driven by steam produced by heating and expansion of groundwater due to an underlying hot source. - During the eruption, ash, and pyroclastic material (rock fragments derived from pre-existing rocks, shown as reworked fragments) are ejected by the volcano. Lava is not produced.

Answer 33

Phreatic The 1st phase of the January 2020 Taal eruption is a phreatic type.

Question 34

- generated by the interaction of magma with abundant surface water. - The contact between magma and surface/ground water causes an explosion due to thermal contraction. As a result, products such as gases, ash, reworked rocks as well as newly formed rocks from the quick cooling of lava (termed juvenile fragments) are ejected by the volcano.

Answer 34

Phreatomagmatic

Question 35

What eruption types are immediate hazards in volcanoes where bodies of water reside in the crater of the volcano. At the same time, these types of eruptions are very hard to predict.

Answer 35

phreatic and phreatomagmatic eruption types

Question 36

characterized by a dense cloud of ash-laden gas along with solid, hot tephra exploding from the crater and rising high above the peak reaching around 5 to 10 km in height generally more explosive than strombolian and is produced by more viscous lava types. Once the volcano "clears its throat," however, the subsequent eruptions can be relatively quiet and sustained.

Answer 36

Vulcanian

Question 37

- characterized by a sustained eruption of large amounts of pyroclastic materials and gases that produces high eruption columns (up to 45 km high). - These eruptive columns produce widespread dispersals of tephra which cover large areas with an even thickness of ash fall deposits. It is considered as the largest and most explosive eruption.

Answer 37

Plinian

Question 38

true or false volcano (especially complex types) may exhibit more than one type of eruption

Answer 38

true - Mayon during its unrest in 2018 have shown both phreatic-phreatomagmatic and strombolian eruptions. - Taal volcano also exhibited different eruption styles during its 1965-1977 unrest.

Question 39

Eruption was recorded (may be oral or folkloric accounts) during historic times (within 600 years) Erupted <10,000 years ago based on geologic evidences (analyses of materials from young volcanic deposits) with local seismic activity

Answer 39

Active Volcanoes

Question 40

How many active volcanoes are there?

Answer 40

24 active volcanoes as of 2020 (Mt. Isarog was added in 2019). Out of the 24, only 21 has historical eruptions.

Question 41

What is the most active volcano

Answer 41

Mt.Mayon followed by Taal volcano island

Question 42

no historical or analytical record of eruption Geologically young (possibly erupted < 10,000 years; for calderas and large systems - possibly < 25,000 years) with young-looking geomorphology (thin soil cover/sparse vegetation; low degree of erosion) and suspected seismic activity along with documented local ground deformation.

Answer 42

Potentially Active 27 volcanoes (e.g., Apo in Davao Region, Natib in Bataan)

Question 43

No record of eruption and its form has been changed by intensive weathering and erosion to form deep and long gullies.

Answer 43

Inactive Volcanoes the term “dormant” is no longer used since Pinatubo was assigned this category but eventually erupted in 1991.

Question 44

How many inactive volcanoes

Answer 44

There are more than 400 inactive volcanoes.

Question 45

- When lava reaches the surface, it can still retain some of its heat for a period of time and can burn objects (such as houses in Hawaii) it comes in contact with. not as dangerous except for low viscosity lavas that can move up to tens of km/hr. generally molten materials, its movement is fluid-like and generally follows deep valleys and other pathways where surface water such as streams would flow downslope, away from the source.

Answer 45

LAVA FLOWS

Question 46

when lavas are still very hot, the viscosity is low allowing them to move in a smooth, billowy, undulating, ropy manner (like melting cheese then you let the melt flow

Answer 46

Pahoehoe

Question 47

as the temperature of the lava decreases, the viscosity increases causing them to form a jagged, stony, rough, or rubbly surface composed of broken lava

Answer 47

Aa

Question 48

pillow-like, rounded lava resulting from quenching. It is formed when lava is in contact with water and are common in the ocean floor (mid-oceanic ridges

Answer 48

Pillow lavas

Question 49

very hot (typically >800 °C) chaotic mixture of rock fragments, gas, and ash that travels rapidly (tens of meters per second) away from a volcanic vent or collapsing flow front. - Due to their temperature and high mobility, they can be extremely destructive and poses the greatest hazard when closest to an erupting volcano.

Answer 49

PYROCLASTIC DENSITY CURRENTS (PDC) - This was demonstrated during the 1902 Mt. Pelee (Martinique) eruption which demolished the coastal city of St. Pierre, killing nearly 30,000 inhabitant.

Question 50

A more diluted (less coarse rock fragments) but more mobile PDC variety

Answer 50

pyroclastic surge or base surge

Question 51

Due to its higher mobility, it is not confined to valleys and can reach ridges

Answer 51

PYROCLASTIC DENSITY CURRENTS (PDC)

Question 52

Umbrella term for fragmented volcanic materials regardless of size.

Answer 52

TEPHRA FALL. When explosive eruptions occur, tephra is ejected into the air and will eventually fall or gravitationally settle downwind of the erupting volcano depending on size.

Question 53

true or false The larger the size and weight of tephra fall, the harder it is to transport

Answer 53

true

Question 54

usually ballistic projectiles that will fall closest to the vent while ash-sized particles may travel hundreds of kilometers and may blanket and accumulate in a wide area.

Answer 54

volcanic bombs

Question 55

true or false - Despite the small size, ash fall deposits may cause infrastructure damage, collapse of roofs, water contamination, and burial along with crop damages. It also poses hazard in health when inhaled and is also a danger in aviation industry.

Answer 55

true

Question 56

generally non-toxic, but can be lethal at large quantities esp. when it displaces oxygen in the air which may lead to asphyxiation of animals and humans. denser than oxygen and is invisible,

Answer 56

CO2 ○ An example of this is the disaster caused by the lake Nyos (Cameroon) in August 1986. Seeping CO2 was initially trapped in the lake bottom. ○ A sudden limnic (CO2) eruption was then trigger by an unknown cause (possibly a landslide), releasing a dense cloud of gas.

Question 57

Is an aerosol that can both cool down the earth’s atmosphere and deplete its ozone concentration for a period of time.

Answer 57

SO2. ○ In the case of the 1991 Pinatubo eruption, 17 million tons of SO2 was injected into the atmosphere. SO2 was converted into sulfuric acid aerosol that prevented the inbound of solar energy from reaching the planet's surface. This resulted to a global temperature drop by about 0.5°C from 1992-1993.

Question 58

Derived from an Indonesian term refers to pyroclastic materials remobilized by water (can be meteoric water, surface water or even melting ice during an eruption. may contain large amount of coarse (up to boulder size) clasts but are still very fluid and can cause direct destruction in its path.

Answer 58

LAHAR During the days of the eruption of Mt. Pinatubo, a typhoon (Yunya) was traversing through Luzon, combining with the ash from the eruption and compounding the hazards from the volcano by inducing lahar flows. Mt. Mayon is another volcano in the Philippines known for creating dangerous lahar flows especially during typhoon seasons

Question 59

A trigger, usually a volcanic earthquake or even an eruption may induce the collapse of the unstable part of the volcano thereby creating a

Answer 59

Landslide/Debris Avalanche. These can create unique geomorphological features such as a horse-shoe shaped crater (e.g. Mt. St. Helens and locally Mt. Iriga in Bicol) in the volcano summit and numerous hills in front of the collapsed sector

Question 60

horse-shoe shaped crater

Answer 60

amphitheater

Question 61

numerous hills in front of the collapsed sector

Answer 61

hummocks

Question 62

generated by volcanoes when (1) landslide deposits or collapsing materials fall into the body of water and cause disturbance and/or (2) explosion directly disrupts the surrounding waters.

Answer 62

Volcanic Tsunami. Examples include the eruption of Krakatau (August 1883) and the recent (December 2018) Anak Krakatau eruption. Locally, Taal volcano is known to produce tsunami-like waves called “seiche” in the Taal caldera lake.

Question 63

○ more acidic waters with enrichment in some volcanic ions in its chemistry; ○ increase in hot spring temperature; ○ changes in volcanic lake water levels, or drying up of nearby springs and wells

Answer 63

Hydrology

Question 64

○ increase in steaming activity; ○ in terms of gas chemistry emission -CO2, SO2 increase; changes in color of steam such as from white to gray may indicate entrained ash

Answer 64

Gas Emission

Question 65

monitored using thermal imaging and can sometimes be noticed through drying up of vegetation around the volcano.

Answer 65

Temperature Increase

Question 66

increased frequency and magnitude of volcanic earthquakes associated landslides (and rockfalls) not associated to hydrometeorological activities

Answer 66

Seismic Activity

Question 67

○ inflation and tilting of the ground measured by geodetic instruments ground fissuring

Answer 67

Ground and Volcano Deformation

Question 68

due to magma intrusion getting closer to the surface

Answer 68

ground fissuring

Question 69

Crater glow due to presence of magma at or near the crater is one of the ways on how to monitor volcanoes

Answer 69

yes

Question 70

Other geophysical measurement basis in monitoring volcanoes

Answer 70

(+GPS Sattelite)

Question 71

- Use of the earth’s natural heat to generate electricity | - A renewable energy resource

Answer 71

GEOTHERMAL ENERGY

Question 72

The geothermal system consists of 4 major parts namely

Answer 72

the heat source, the reservoir rock the fluid the cap rock

Question 73

usually the young (<100,000 years) magma being intruded to shallow levels (<6 Km) in the crust.

Answer 73

the heat source,

Question 74

serves as the storage of the geothermal fluids so it must be permeable and porous

Answer 74

the reservoir rock

Question 75

carries the heat and must be sufficient enough to sustain hydrothermal convection

Answer 75

the fluid meteoric, connate, groundwater seawater

Question 76

is an impermeable layer (usually clay) that prevents the water from migrating to the surface thus increasing the fluid pressure and heat capacity of the geothermal system

Answer 76

the cap rock

Question 77

largest geothermal field in the Philippines and considered as the largest wet-steam field (a type of geothermal power plant) in the world.

Answer 77

Tongonan

Question 78

most recent field to be added in the list of producer of geothermal energy

Answer 78

The Maibarara field

Question 79

How many active geothermal production fields in the Philippines

Answer 79

7 active geothermal production fields in the Philippines.

Question 80

As of 2019, the Philippines is the ____ largest producer of geothermal energy in the world after the _______ and ______

Answer 80

As of 2019, the Philippines is the 3rd largest producer of geothermal energy in the world after the United States and Indonesia.