5_Volcanic_Hazards geological hazard impending signs of volcanic eruption

Disaster Risk Reduction Management

1. Disaster Readiness and Risk Reduction

2. Chapter 5 Volcanic Hazards

3. To identify various potential volcanic hazards; To recognize the natural signs of an impending volcanic eruption and other volcanic hazards To analyze the effects of the different volcanic hazards To interpret different volcanic hazard maps To apply precautionary and safety measures before, during , and after an eruption Learning Objectives

4. Section 5.1 Lava Flow

5. Types of Lava Flow Basaltic L ava F lows T he fastest flowing because of their relatively low viscosity U sually associated with the broad landforms of shield volcanoes Lava flow styles are Pahoehoe and A‘a . The former is composed of thin flows with smooth surface that sometimes feature ropy folds, while the latter flows have sharp, spiny surfaces.

6. Types of Lava Flow Andesitic Lava Flows Typically associated with stratovolcanoes and commonly form lava domes Have small volume so they do not usually go beyond the foot of the volcano Because of their viscous nature, the surface of andesitic flows is comprised of smooth-sided fragments called block lava flows as the surface fragments are loosely termed blocks S low by lava flow standards

7. Types of Lava Flow Rhyolitic Lava Flows Have relatively higher viscosity which is why it is a lot slower than andesitic and basaltic flows U sually associated with violent eruptions involving pyroclastic flows and with very steep landforms such as lava domes and lava spines Flow out of a volcano after the pyroclastic flow event

8. Types of Lava Flow Sheet Lava F lows Have are thicker than pahoehoe and have surface textures ranging from ropy to striated Are associated with violent eruptions Usually collapse as a result of the emptying of lava below the hardened surface Pillow Lava Flows Pillow-shaped rocks formed by the sudden cooling of lava that is deposited underwater

9. Activity 1 OBJECTIVE: This activity will let the students correctly identify the type of volcano and infer the eruption character of each from the shape and size or the height and width of the volcano as measured on a topographic map.

10. Effects of Lava Flows Deaths attributed to lava flows are often due to related causes, such as: Explosive shower of molten spatter over a wide area when lava interacts with water E xplosion of methane gas produced by lava burial of vegetation A sphyxiation due to accompanying toxic gases P yroclastic flows from a collapsing dome of thick viscous lava flows Floods and lahars from ice and snow meltwater or from the damming of tributaries Lava flows bring damage or total destruction to land and property by burying, crushing, or burning everything in their paths. Lava flows also bury vegetation.

11. Factors in Lava Flow Hazard Zoning Viscosity of lava flows Effusion rate Slope of the land

12. Activity 2 OBJECTIVE: This activity will let the students provide bases for one of the methods of constructing lava flow hazard maps.

13. Section Assessment What are the three major types of magma? How do these differ , chemically and physically? In terms of plate boundaries, where are the different types of magma generated? What magma properties dictate the explosiveness of volcanic eruptions? What characteristics of lava flows make them more dangerous or less dangerous than other volcanic deposits and events? Enumerate ways by which communities near volcanoes can be protected from lava flows .

14. Section 5.2 Volcanic Gases

15. Volcanic Gases during Eruption

16. Volcanic Gases during Eruption The most abundant volcanic gas released into the atmosphere is water vapor (H 2 O ). Other volcanic gases include CO 2 , SO 2 , and trace amounts of N, H, CO, S, Ar , Cl , and F. These gases combine with hydrogen and water to produce toxic compounds, such as HCl , HF, H 2 SO 4 , H 2 S. These gases leave the emission sites as acid aerosols, as compounds adsorbed on tephra, and as microscopic salt particles.

17. Examples of Volcanic Gas Compositions in Volume Percent Concentrations

18. Activity 1 OBJECTIVE: This activity will let the students determine what makes carbon dioxide dangerous and how to avoid its fatal effect .

19. Toxicology of Volcanic Gases

20. Toxicology of Volcanic Gases

21. Volcanic Gas Danger Zones Hazard zones for volcanic gases escaping through emission sites (e.g ., craters , vents, fissures , or hydrothermal features ) are typically restricted close to these. Gas emission site locations, low-lying areas in which dense gases can accumulate , and wind directions that favor gas accumulations are all reflected in defining hazard zones. Areas subject to the greatest hazard from “poisonous” gases will be downslope from emission sites and along the direction of the wind.

22. Example of a Volcanic Gas Hazard Map

23. Activity 2 OBJECTIVE: This activity will let the students l earn about SO 2 effects , dispersion, and hazard mapping .

24. Safety Measures against Volcanic Gases When volcanoes continually emit toxic gases that may be associated with the deposition of fluorine and other trace elements, evacuation and resettlement of the affected population is the only viable solution. In situations where critical concentrations of volcanic gases such CO 2 and CO as are emitted only occasionally on both active and dormant volcanoes, automated gas alarms are being used. Among the most important protective gadgets that people should have for protection from toxic gases and dusts are face masks.

25. Safety Measures against Volcanic Gases To prevent worsening of pre-existing non-communicable respiratory diseases, interstitial lung diseases, and pulmonary vascular diseases by acid rains, gases, and ash, the following actions are recommended: Drink fluids to encourage loosening of secretions and coughing. During periods of volcanic pollution, avoid contact with people who have colds. Avoid smoking and inhaling second-hand as smoke will only add to breathing problems. Avoid overexertion. In heavy pollution, stay indoors, close windows and doors, turn on air conditioners Use gas masks.

26. Section Assessment How does seawater find its way to the surface through volcanoes? In what forms do the different volcanic gases spread from emission sites? In what ways may the above forms and types of volcanic gas be hazardous to one‘s health? In situations where evacuation cannot be carried out right away, what personal safety measures can one adopt as protection from the effects of volcanic gases?

27. Section 5.3 Pyroclastic Flows

28. How Pyroclastic Flows Occur Pyroclastic flows are hot mixtures of fresh lava, gas, rock, pumice, and ash that move down the sides of a volcanic crater at high speeds during an eruption. The materials may come from the collapse of lava dome at or close to the summit or from the materials going back down from an eruption column that cannot go farther into the air. The mobility and speed of pyroclastic flows are derived from its gas content and from the heat of its components that further generates more gases. Pyroclastic flows are common in volcanoes composed of andesite and of the more viscuous , dacitic , and rhyolitic rock types — rocks that comprise volcanoes displaying more violent eruptions.

29. Mechanisms of Pyroclastic Flow Generation

30. Activity 1 OBJECTIVE: This activity will let the students correctly identify pyroclastic flow deposits from pictures of samples and outcrops.

31. Effects of Pyroclastic Flows Burn Impact and burial Inhalation of hot ash and gases Lahars and flooding

32. Activity 2 OBJECTIVE: This activity will let the students make a reasonable pyroclastic flow hazard map for a volcano and provide appropriate explanation .

33. Section Assessment How do the two pyroclastic flow-generating dome collapse processes ( Merapi and Pelean ) differ in terms of driving force? How do you distinguish a dome-collapse type of pyroclastic flow deposits from those due to collapse of the eruption column (Soufriere )? Describe the transformation of pyroclastic flow deposits into lahars. What damages can be seen along the path of a pyroclastic flow and lahar? Name ways by which pyroclastic flow hazard maps may be used as safety guides by planners and residents.

34. Section 5.4 Tephra Falls and Ballistic Projectiles

35. Tephra Falls Tephra refers to volcanic rock and lava materials that are ejected into the air by explosions or carried upward by eruption column‘s hot gases or lava fountains. Tephra falls, which skip hugging the slope and go directly to the ground, range in size from less than 2 mm to more than 1 m in diameter. Large-sized tephra typically falls back to the ground on or close to the volcano and progressively smaller fragments are carried away from the vent by wind . Ash can travel hundreds to thousands of kilometers downwind from a volcano.

36. Ballistic Projectiles Ballistic projectiles are a special kind of tephra. These follow a projectile path as these are forced out of the vent at steep angles like a cannon ball. They consist of bombs, blocks, and lapilli.

37. Types of Tephra Deposits According to Size Ash ‒ fragments 2 mm in diameter; mix of broken glass and pulverized rock Lapilli ‒ fragments 2–64 mm in diameter; bigger pumice fragments mixed with finer ash Blocks and Bombs ‒ fragments 64 mm and bigger in diameter; bombs are molten when ejected and assume various shapes upon cooling; blocks are large broken pieces of solid vent material or surrounding rocks

38. Types of Tephra Deposits According to Origin , Composition , and Texture, as Well as Appearance

39. Activity 1 OBJECTIVE: This activity will let the students correctly identify tephra fall deposits from pictures of samples and exposures .

40. Dangers From Tephra Falls and Ballistic Projectiles Airborne fine particles are a health hazard. Ash is made up of pulverized rock but can be extremely heavy if it gets wet. People should watch out for ash accumulation on roofs as this may cause the roofs to cave in and cause injury or even death .

41. Dangers From Tephra Falls and Ballistic Projectiles Tephra fall and ballistic projectiles also endanger life, property, and the environment in the following ways: Small scoria pieces can be embedded in wood and can even dent metals. Even thin (<2 cm) falls of ash can damage critical facilities (e.g., hospitals, electric-generating plants , and pumping stations ); can short circuit electric-transmission facilities, telephone line radio and television transmitters ; and block the flow of surface-drainage systems. Ash clogs filters and vents of motors, industrial machines, and nuclear power plants ; may clog air filters of vehicles including those of jet engines; and abrasion of moving parts (bearings, brakes, and transmissions) and bodies of automobiles.

42. Dangers From Tephra Falls and Ballistic Projectiles Tephra fall and ballistic projectiles also endanger life, property, and the environment in the following ways: Airborne ash can reduce visibility to zero and turn day to night by blocking sunlight. Volcanic projectiles have temperatures above ignition points. Initial temperatures of projectiles generated from new magma may reach up to 1100°C. Upon impact, temperatures may well be above the ignition point for vegetation and a variety of man-made objects . Some pyroclastic falls contain toxic gases, acids, salts, and chemicals that can be absorbed by plants and water bodies, which can be dangerous to people and other living things. Tephra can change rainfall or runoff relationships. Low permeability of hardened ash deposits leads to increased runoff , accelerated erosion, and floods ; thick, coarse-grained deposits retain water and eliminate surface runoff.

43. Activity 2 OBJECTIVE: This activity will let the students construct a simple ashfall hazard map from available information .

44. Precautions for Tephra Fall

45. Section Assessment In what conditions do the nest tephra fall fragments not fall back to the ground right away ? What are the consequences of this? How are ejected tephra fragments “winnowed”? What factors affect the extent and distribution of the different types of tephra and projectiles? What was the biggest cause of deaths during the Pinatubo ashfalls ? What contributed to these incidents? List three things that you need to do to protect your family‘s health and lives from tephra falls and ballistic projectiles.

46. Section 5.5 Lahars

47. What I s Lahar? A lahar is the process wherein wet cement-like mixture of volcanic material and water flows down the slopes of a volcano. Lahar usually carries fresh eruption material like pyroclastic flows and tephra fall and also picks older volcanic deposits along the river channel. Large lahars which can flow at a rate of several tens of meters per second, are impossible for people to outrun. The deposits that lahar leave behind are like dry concrete, sometimes with boulders as big as a house scattered everywhere.

48. How Are Lahars Generated? Many lahars are formed by intense rainfall during an eruption. Rainwater can easily erode loose volcanic material deposited on the upper slopes of a volcano or along the path of a river on its way down the slopes. Eruptions alone can trigger lahars directly by melting snow and icecap. The breaching of the dam or crater lake by the eruption may also provide the water that loosens and carries volcanic materials from the upper slopes .

49. Activity 1 OBJECTIVE: This activity will let the students differentiate lahar from pyroclastic flow deposits from pictures of exposures .

50. Effects of Lahars Lahars pose danger to people because of the large volume of materials involved and the speed by which they deliver these materials. Lahars can cause serious economic and environmental damage to large floodplain areas and to those affected by the severed lifelines. Large tracts of agricultural lands and residential areas may be buried by one or more pulses of lahar deposition. Roads may be blocked and bridges destroyed thereby seriously hampering the normal flow of people and goods. After a river channel had been filled by lahar, severe flooding and extremely high rates of sedimentation may follow. Debris of all sorts may form a dam along a river and breaking of the dam may lead to flash floods and more lahars downstream.

51. Activity 2 OBJECTIVE: This activity will let the students i dentify the bases for constructing lahar hazard map for a volcano and provide appropriate explanation .

52. Preventive Measures during Lahars Evacuation would be the best preventive measure. During a lahar crisis, effective dissemination of lahar hazard information is necessary. A good monitoring and warning system should be in place , just in case, to alert people early enough so that they can evacuate to safer places. Many methods have been used to stop or at least detour a lahar. including building retention basins, alternate channels, tunnels, and concrete structures such as dams across the river channel and dikes parallel to the channels.

53. Section Assessment What components and conditions are needed to generate lahars? How is it relevant to distinguish lahar deposits from non-lahar deposits? How important is it to differentiate types of lahars? In what ways do the effects of lahar differ from those of flooding by river water? How can science and technology contribute to the understanding of lahar and to the mitigation of its effects to communities?

54. Section 5.6 Volcanic Debris Avalanche

55. What Are Volcanic Debris Avalanches? Volcanic debris avalanches are landslides that occur in volcanic slopes. Compared with non-volcanic landslides, debris avalanches are faster and their deposits more far-reaching mainly due to the large amount of material involved. Debris avalanche may involve collapse of the volcano‘s flank or of one big sector of the volcano including that of its top. A debris avalanche deposit may not be entirely as hot as a lava flow or pyroclastic flow but the abnormally large volumes of volcanic material traveling at great speeds will bury areas far and wide.

56. Activity 1 OBJECTIVE: This activity will let the students understand how a bulge develops on the slope of a volcano and how an avalanche might trigger an explosive eruption .

57. Recognizing a Debris Avalanche The occurrence of debris avalanche leaves a very prominent gap in the cone of the volcano as well as a landscape-altering voluminous deposit. The gap is called amphitheater because of the horseshoe-like shape of the crater left behind by the volcano‘s collapse.

58. Triggering Mechanisms of Volcanic Debris Avalanche Some of the triggering mechanisms and conditions within a volcano and its slopes that lead to a large volcanic debris avalanche

59. How Deadly Can a Debris Avalanche Be? Debris avalanches greatly alter the pre-existing topography by creating deep horseshoe-shaped craters and by burying and destroying everything in their paths. Debris avalanche deposits that are thick enough can block streams to form lakes. Sudden break-out of the lake water could generate lahars and floods. Lahars and floods can be a direct result of the dewatering of a debris avalanche deposit. By removing a large part of a volcano’s cone, debris avalanches can abruptly depressurize hot magma and the surrounding hydrothermal systems. This may result in explosions ranging from small steam explosions to large steam- and magma-driven directed blasts.

60. Activity 2 OBJECTIVE: This activity will let the students use topographic map skills to interpret the debris avalanche deposit of Mt. Iriga . Also, this activity will let the students draw profile views of Mt. Iriga “before” and after the debris avalanche . These profiles will be used to interpret the changes in the mountain’s topography that were caused by the debris avalanche .

61. Hints That People May Use to Alert Themselves of a Possible Occurrence of Debris Avalanche Sudden appearance of springs, seeps, or saturated ground New cracks and/or bulges in the ground, pavements or sidewalks Soil moving away from foundations Broken water lines and other underground utilities Tilting of telephone poles, trees, retaining walls, or fences Offset fence lines Down-dropped road beds Sudden rise or decrease in stream water levels that is not related to rainfall A faint rumbling sound (frequency increases as landslide nears) Unusual sounds, such as trees cracking or boulders knocking together, might indicate moving debris V olcanic activity or nearby seismicity

62. Section Assessment Name features that indicate the occurrence of debris avalanche. What are the conditions that you must look for to say that a volcano is ripe for an avalanche once triggered. Describe a post-debris avalanche scenario where a housing area and a commercial center just beside the coastline used to be before being hit by a debris avalanche from a nearby volcano? What would be the best thing to do to ensure one‘s safety from debris avalanche?