Unit 9 Exam Questions Flashcards
Suggest two reasons why some places within volcanic regions have a very high hazard level. (6 marks)
Proximity to the Vent
Areas located close to the volcanic vent experience the most intense hazards due to exposure to primary volcanic phenomena such as pyroclastic flows, lava flows, and tephra (volcanic ash and rock fragments). Pyroclastic flows, consisting of hot gas and volcanic materials, can travel at speeds of over 100 km/h and reach temperatures of 1000°C, making them one of the deadliest hazards. For example, in the 1902 eruption of Mount Pelée in Martinique, a pyroclastic flow destroyed the city of Saint-Pierre within minutes, killing nearly all of its 30,000 inhabitants.
Topography and Wind Influence
The shape of the land (relief) can amplify the hazard level. Valleys and steep slopes can direct and accelerate pyroclastic flows and lahars (volcanic mudflows), increasing the risk in certain areas. Additionally, prevailing winds can determine the spread of volcanic ash, which can travel thousands of kilometers. For instance, during the 2010 eruption of Eyjafjallajökull in Iceland, ash clouds were carried across Europe by prevailing winds, disrupting air travel for weeks.
Suggest two reasons for variations in ash fallout from a volcanic eruption (6 marks)
Wind Direction and Strength
The prevailing westerly winds carried ash from the eruption in a predominantly eastward direction.
Stronger winds increase the dispersion distance, while weaker winds lead to more localized ash deposits.
Variability in wind direction on different days influenced the spread of ash in different directions, as seen in the map.
Height of the Eruption Column and Ash Load
The higher the volcanic ash column, the further ash can travel due to the influence of atmospheric currents.
Ash particles settle at different rates:
Larger particles (e.g., volcanic bombs) fall close to the vent.
Fine ash can remain suspended in the atmosphere for long distances before settling.
The eruption’s intensity influences how far ash spreads—stronger eruptions inject ash higher into the stratosphere.
Proximity to the Volcano
Areas closer to the vent experience thicker ash deposits due to the immediate fallout of heavier material.
As distance increases, ash deposition becomes thinner and more dispersed.
Topography and Ash Accumulation
Valleys and mountain ridges channel ash movement, influencing local patterns.
For example, ash may accumulate more in valleys due to wind funnelling, while high ridges might receive less deposition.
Explain the variations in the warning times and hazard durations of different natural disasters.
Earthquakes – Shortest Warning Time, Short Duration
Warning Time:
Earthquakes happen suddenly when stress is released along cracks in the Earth (faults).
There may be small signs like tiny quakes (foreshocks) or gas changes, but they are not reliable.
So, warning time is very short – just seconds or minutes before the shaking starts.
Hazard Duration:
The actual shaking usually lasts just a few seconds to a couple of minutes.
But aftershocks, landslides, tsunamis, and fires can cause damage for days or even weeks.
Hurricanes – Moderate Warning Time, Moderate Duration
Warning Time:
Hurricanes form slowly over several days above warm oceans.
Weather satellites and forecasts can track them early, giving people several days to prepare or evacuate.
Hazard Duration:
The worst part of the storm usually lasts a few hours to 2 days.
But flooding, storm surges, and damaged roads and homes can cause problems for weeks after.
Volcanic Eruptions – Longest Warning Time, Longest Duration
Warning Time:
Volcanoes often give weeks to months of warning.
Signs include earthquakes, gas release, and bulging ground as magma rises.
Hazard Duration:
Eruptions can last a very long time – from days to years.
Example: Kīlauea volcano in Hawaii erupted for 35 years (1983–2018).
Volcanoes can keep causing problems with lava flows, ash clouds, and toxic gases.
Explain two reasons why the number of deaths from mass movement events varies. (6 marks)
- Physical Factors – Simple Explanation
Steep Slopes:
Steeper slopes are more likely to have fast and dangerous landslides.
These can cause more deaths, especially in mountain areas like the Himalayas and Andes.
Type of Rock or Soil:
Loose materials like clay, sand, or volcanic ash soak up rainwater easily and can collapse quickly after heavy rain.
Harder rocks like granite may break into big chunks, but usually cause smaller rockfalls that only affect small areas.
Heavy or Long Rainfall:
When it rains a lot, the ground becomes too wet, and the slope can collapse.
Example: In 2006, heavy rain caused a deadly landslide in Leyte, Philippines, burying a village.
- Human Factors – Simple Explanation
Population Density:
Places with lots of people living close together are at higher risk when landslides happen.
If homes are built on unstable land, the damage is worse.
Quality of Buildings:
In poorer countries, many buildings are not strong, so they collapse easily.
In richer countries, better building rules and land planning help keep people safer.
Warning Systems and Preparation:
Some countries (like Japan and the USA) have early warning systems.
This means they can evacuate people early, which saves lives.
Countries without warning systems often suffer more deaths.
Explain why volcanoes are not found at all types of tectonic plate boundaries. (6 marks)
Where Volcanoes Do Happen:
1. Divergent Boundaries (Plates move apart)
Plates move away from each other, leaving a gap.
Magma from the mantle rises through the gap and creates volcanoes.👉 Example: Mid-Atlantic Ridge, where underwater volcanoes form.
2. Convergent Boundaries (One plate goes under another)
An oceanic plate sinks under a continental plate.
The oceanic plate melts and turns into magma.
The magma rises and forms volcanoes.👉 Example: Andes Mountains in South America.
Where Volcanoes Don’t Happen:
3. Collision Boundaries (Two continental plates crash)
When two land plates push into each other, neither one sinks.
No magma is made, so no volcanoes form.
Instead, mountains form by folding the land.👉 Example: Himalayas – big mountains, but no volcanoes.
4. Conservative Boundaries (Plates slide past each other)
Plates move side by side, not apart or under.
No magma is formed because the crust is not destroyed.👉 Example: San Andreas Fault in California – earthquakes happen, but no volcanoes.
火山会出现的地方：
1. 发散边界（板块分开）
板块彼此分开，形成裂缝。
地幔中的岩浆上升，通过裂缝喷发，形成火山。👉 例子：大西洋中脊，那里有海底火山。
2. 汇聚边界（一个板块下沉）
海洋板块俯冲到大陆板块下面。
被俯冲的板块在高温下熔化，形成岩浆。
岩浆上升，形成火山。👉 例子：南美洲的安第斯山脉。
火山不会出现的地方：
3. 碰撞边界（两个大陆板块相撞）
两块大陆板块相撞时，谁也不下沉。
没有岩浆产生，所以不会形成火山。
相反，地壳变厚、褶皱，形成高山。👉 例子：喜马拉雅山，有高山但没有火山。
4. 转换边界（板块擦身而过）
板块不是分开也不是下沉，而是沿着边界滑动。
没有岩浆产生，也没有火山活动。👉 例子：加州的圣安德烈亚斯断层，有地震，但没有火山。
Explain why the depth of focus of earthquakes varies from place to place. (6 marks)
- Shallow Earthquakes (0–70 km deep)These happen near the Earth’s surface.
Found where plates move apart (divergent boundaries) or slide past each other (transform boundaries).
When plates move apart, cracks form in the crust, causing shallow quakes.
When plates slide past, they can get stuck. When they suddenly move, it causes strong shallow earthquakes.👉 Example: San Andreas Fault in California. - Medium (Intermediate) Earthquakes (70–300 km deep)These happen at subduction zones, where one plate goes under another.
As the ocean plate sinks, it bends and breaks deeper inside the Earth.
This causes earthquakes at deeper levels.👉 Example: Nazca Plate going under the South American Plate (Andes Mountains). - Deep Earthquakes (300–700 km deep)Only happen in subduction zones.
The sinking plate goes very deep into the mantle.
High heat and pressure cause rocks to change form, which releases energy as deep earthquakes.
These quakes are usually less damaging because they are far from the surface.👉 Example: Japan Trench – Pacific Plate going under the Eurasian Plate. - 浅层地震（深度0–70公里）这些地震发生在地表附近。
多出现在板块分离的地方（发散边界）或相互擦过的地方（转换边界）。
当板块分开时，地壳拉裂，形成裂缝，引发浅层地震。
当板块滑动时卡住，突然释放能量，就会产生强烈的浅层地震。👉 例子：美国加州的圣安德烈亚斯断层。 - 中层地震（深度70–300公里）这些地震发生在俯冲带，也就是一个板块被另一个板块压到下面的地方。
海洋板块下沉过程中会弯曲、破裂，在更深处引发地震。👉 例子：纳斯卡板块正在俯冲到南美板块之下（安第斯山脉）。 - 深层地震（深度300–700公里）只出现在俯冲带。
被压下去的板块会沉到地幔深处。
高温和高压会使岩石改变结构，从而释放能量形成深层地震。
因为震源很深，这类地震在地表的破坏较小。👉 例子：日本海沟——太平洋板块俯冲到欧亚板块下面。
Explain why the location of tornadoes varies. (6 marks)
- Different Air Types MeetTornadoes happen when warm, wet air meets cold, dry air. This creates powerful storms.
In the USA, especially in Tornado Alley (like Texas and Oklahoma), warm air from the Gulf meets cold air from the Arctic.
The land is flat, so storms can grow easily.
Other places like Bangladesh, Argentina, and South Africa also have this kind of air meeting, so tornadoes happen there too. - Seasons and Weather
Tornadoes are more common in spring and summer when the air is warm and unstable.
They are rare in winter because the air is cooler and more stable.
Climate change might change where tornadoes happen by moving the jet stream (a strong wind in the atmosphere). - Land Shape (Topography)
Flat land, like in the central USA or Argentina, helps tornadoes form because nothing blocks the air.
Mountains, like the Rockies or the Himalayas, stop air from moving smoothly, so tornadoes are less common there. - 不同气团的相遇当温暖潮湿的空气遇到寒冷干燥的空气时，就可能形成强烈的雷暴，从而产生龙卷风。
在美国的“龙卷风走廊”（例如德克萨斯州和俄克拉荷马州），来自墨西哥湾的暖湿空气和来自北极的冷干空气相遇。
地势平坦，有利于风暴发展。
像孟加拉国、阿根廷和南非也有类似的气团碰撞，因此这些地方也会发生龙卷风。 - 季节和气候
春季和夏季空气更温暖、更不稳定，所以龙卷风更常见。
冬季空气较冷且稳定，龙卷风较少。
气候变化可能会改变龙卷风出现的区域，因为它会影响喷流（高空强风）的移动。 - 地形影响
平坦的地形，如美国中部或阿根廷草原，有利于龙卷风形成，因为空气流动不受阻挡。
高山如落基山脉或喜马拉雅山，会阻挡空气流动，龙卷风较少出现。
Is there a relationship between the number of tornadoes and the number of tornado-related deaths?
- Tornado Strength and PopulationNot all tornadoes are deadly. Tornadoes are ranked from EF0 (weak) to EF5 (very strong).
Many weak tornadoes (EF0–EF1) might cause little or no deaths.
But one strong tornado (EF4–EF5) hitting a city can kill many people.👉 Example: In 2011, a strong EF5 tornado in Joplin, Missouri killed 158 people, even though there weren’t many tornadoes that year. - Early Warnings Save LivesBetter weather radar, sirens, phone alerts, and emergency plans help people escape in time.
More people die when tornadoes happen with no warning or at night when they’re asleep.👉 Example: In 2013, a big tornado hit Moore, Oklahoma. Because of good warnings, fewer people died compared to past tornadoes. - Buildings and Safety Plans
In areas with good storm shelters and strong buildings, fewer people die.
In places with weak homes (like mobile homes), tornadoes can be more deadly.👉 Example: In 2020, a tornado in Tennessee killed many people in places with old or weak buildings. - Time and Place Matter
Tornadoes that happen in winter or at night are more dangerous because people are not ready.
Some countries (like the USA, Bangladesh, and Argentina) have more deaths based on where people live and how well prepared they are. - 龙卷风强度与人口密度不是所有龙卷风都很致命。龙卷风根据EF等级从EF0（弱）到EF5（非常强）。
很多弱龙卷风（EF0–EF1）几乎不会造成死亡。
但如果一个强龙卷风（EF4–EF5）袭击城市，就可能造成大量死亡。👉 例子：2011年，美国密苏里州乔普林市发生了EF5级龙卷风，造成158人死亡，尽管那一年龙卷风总数并不多。 - 预警系统的进步更好的雷达、警报器、短信提醒和应急预案可以帮助人们及时避难。
如果龙卷风突然发生或发生在夜晚，人们没有准备，会导致更多死亡。👉 例子：2013年，美国俄克拉荷马州摩尔市遭遇EF5级龙卷风，因为有充分的预警，死亡人数比以往同等级龙卷风少很多。 - 建筑结构与防灾准备
有防风地堡和坚固建筑的地方，死亡率较低。
拥有简陋房屋（如移动房屋）的地区更容易发生死亡。👉 例子：2020年，美国田纳西州的龙卷风中，许多死亡发生在老旧或不抗风的建筑中。 - 季节和地区的影响
冬天或夜晚发生的龙卷风更危险，因为人们正在睡觉，不容易反应。
像美国、孟加拉国和阿根廷这样的国家，死亡人数的差异取决于人们的居住位置和应急准备情况。
Suggest how the mudflows are formed
- Where the Water Comes FromMudflows need a lot of water to start. This water can come from:
Glaciers or snow melting because of volcanic heat.
Heavy rain soaking ash and loose rocks, making them slippery.
A crater lake or a landslide suddenly collapsing and releasing water.👉 Example: In 1985, a volcano in Colombia (Nevado del Ruiz) caused a mudflow that killed over 23,000 people in the town of Armero. - Mixing Water and Volcanic StuffThe water moves downhill and mixes with ash, soil, and rocks from the volcano.This creates a thick, fast-moving muddy flow.If the volcano has steep sides (like Mount Rainier), gravity makes the mudflow move faster and erode more land.
- How the Mudflow MovesMudflows usually go down river valleys or drainages, so they can travel very far — even over 100 km.👉 Example: The mudflows from Mount Rainier (called Electron and Osceola) moved into nearby lowland areas and left behind thick layers of volcanic mud.As the mudflow spreads out in flatter areas, it covers large regions in thick volcanic material.
- 水的来源泥流需要大量水才能开始。水可以来自：
火山热量导致的冰川或积雪融化。
大雨把火山灰和松散岩石弄湿，使它们变得滑并容易移动。
火山口湖或山体滑坡突然崩塌，释放出大量水和碎片。👉 例子：1985年哥伦比亚的内瓦多-德鲁伊斯火山爆发，导致泥流掩埋了阿梅罗镇，造成超过23,000人死亡。 - 水与火山物质混合水往山下流动时，会带走火山灰、岩石碎片和泥土，形成一种浓密而快速流动的泥浆。如果火山坡度很陡（比如雷尼尔山），重力会让泥流更快、更有冲击力。
- 泥流的流动路径泥流通常沿着河谷或排水沟流动，因此它们能移动很远（有时超过100公里）。👉 例子：雷尼尔山的泥流（Electron 和 Osceola）沿自然山谷流向普吉特低地，并留下大量泥沙。当泥流到达低地时，它会扩散开来，覆盖大片地区，留下厚厚的火山物质。
What effects the shaking intensity of an earthquake?
The shaking intensity of an earthquake depends on how energy spreads, the ground type, and local conditions.
Firstly, distance from the epicenter is important. The closer you are, the stronger the shaking, because the energy is released from that point. As the seismic waves travel outward, they lose energy (attenuation), so shaking becomes weaker further away.
Secondly, local geology affects how shaking feels. Soft ground like clay or sand amplifies the waves, making shaking feel stronger, even far from the epicenter. Hard bedrock absorbs the waves, so shaking is less intense.Example: In the 1989 Loma Prieta earthquake, parts of San Francisco built on soft ground suffered more damage than areas on solid rock.
Thirdly, the direction of the fault rupture can focus energy in some directions more than others. This means that shaking might be stronger in one area even if it is farther from the epicenter, depending on how the fault moved.
Finally, shaking reports from people can be affected by building design. Poorly built structures amplify vibrations, while earthquake-resistant buildings reduce shaking, which can influence the reported intensity on shaking maps.
So, shaking intensity is affected by distance, ground type, fault direction, and how people experience and report the shaking.
地震的震感强度取决于能量如何传播、地面类型和当地条件。
首先，离震中距离的远近非常关键。离震中越近，震感就越强烈，因为能量是从那里释放出来的。随着地震波向外传播，能量会逐渐衰减，所以越远的地方震感越弱。
其次，当地的地质条件也会影响震感。像粘土或沙子这样松软的地面会放大地震波，即使离震中较远，震感也会很强。相比之下，像花岗岩等坚硬的基岩会吸收地震波，震感就会较轻。例子：在1989年洛马普列塔地震中，旧金山建在软土上的区域（如Marina区）受到的破坏比建在坚硬岩石上的地区更严重。
第三，断层破裂的方向也会影响震感。地震时，能量沿着特定方向传播，有时会集中在一个方向，使得某些地方即使离震中远，也感受到更强烈的震动。
最后，人们的报告和建筑结构也影响震感的记录。建筑质量差的地区更容易感受到强烈震动，而抗震设计良好的建筑可以减弱震感，从而影响人们对震感强度的主观感受和报告数据。
因此，震感强度受到震中距离、地面类型、断层方向和人们的感知与建筑结构的共同影响。
Explain why some areas are more prone to landslides than others. (6 marks)
Steep Slopes and Weak Rocks
Areas with steep hills or mountains are more at risk because gravity pulls the soil and rocks down.
If the rocks are soft or loose, like clay or shale, they can easily break apart, especially when wet.
Example: The Himalayas and Andes have lots of landslides because they are steep and made of weak rock.
Heavy Rainfall
Lots of rain makes the ground wet and heavy, which can cause slopes to collapse.
Storms or monsoons can also quickly wash away the soil and cause mudslides.
Example: In Pakistan (2010), heavy rain caused landslides that made thousands of people lose their homes.
Human Activities
Cutting down trees (deforestation) removes roots that help hold soil in place.
Building houses on hills (urbanization) adds weight and can make slopes unstable.
Example: In Rio de Janeiro, poor communities built on hills often have landslides during rainstorms.
陡峭的坡度和弱岩层
有陡坡或山地的地方更容易发生滑坡，因为重力会拉动岩石和土壤向下滑动。
如果岩石是松散或软弱的（如粘土或页岩），遇水后更容易崩塌。
例子：喜马拉雅山和安第斯山经常发生滑坡，因为地形陡峭，岩层不稳定。
强降雨和地面饱和
大量降雨会使地面变得潮湿而沉重，导致山坡崩塌。
暴雨或季风也会快速冲刷山坡，引发泥石流或滑坡。
例子：在2010年的巴基斯坦，强季风降雨引发了滑坡，成千上万人被迫撤离家园。
人类活动（砍伐森林和城市扩张）
砍树（森林砍伐）会破坏树根，失去固定土壤的作用。
在陡坡上建房会增加重量，使斜坡变得不稳定，容易崩塌。
例子：在巴西里约热内卢，许多贫民窟建在山坡上，每当下大雨时就经常发生致命滑坡。
Briefly explain two causes of landslides other than earthquakes. (6 marks)
- Heavy Rainfall and Water SaturationIntense or long-lasting rain adds water to the soil, making it heavier and more likely to slide.Water also fills spaces between soil particles, reducing friction and making the slope unstable.Example: In 2010, monsoon rains in Pakistan triggered massive landslides that displaced thousands in mountainous regions.
- Deforestation and Human ActivitiesCutting down trees removes roots that help hold soil together, making slopes easier to collapse.Building homes or roads on steep hills adds extra weight and weakens the ground.Example: In Rio de Janeiro, Brazil, many informal homes built on steep, deforested slopes suffer deadly landslides during heavy rain.
- 强降雨和土壤饱和持续的大雨或强降雨会让土壤吸收大量水分，使斜坡变得更重，更容易滑动。水分进入土壤后会增加孔隙水压力，减少颗粒间的摩擦力和黏合力，导致坡面失稳。例子：在2010年，巴基斯坦的季风暴雨引发了大规模滑坡，造成山区数千人流离失所。
- 砍伐森林和人类活动砍树会破坏树根系统，而树根本来能固定土壤、减少侵蚀，没有植被的斜坡更容易崩塌。在陡坡上建房或修路会给地面增加额外负重，加剧滑坡风险。例子：在巴西里约热内卢，很多建在陡峭、被砍伐的山坡上的贫民区，在暴雨后经常发生致命滑坡。
Explain the factors which influence the hazard of soil liquefaction. (6 marks)
- Soil Type and Water ContentLiquefaction is more likely in loose soils like sand and silt, especially if they are waterlogged.High water tables or heavy rain increase the risk by making the soil less stable.Example: In 2011, the Christchurch Earthquake (New Zealand) caused severe liquefaction in sandy, wet ground.
- Earthquake Strength and DepthStronger earthquakes that last longer shake the ground more, increasing liquefaction risk.Shallow earthquakes are especially dangerous because they cause more intense shaking.Example: In 1964, the Niigata Earthquake (Japan) caused liquefaction that tilted buildings.
- Location and Water BodiesAreas near rivers, coasts, or reclaimed land are at greater risk because of high water levels and loose soil.Example: The 1989 Loma Prieta Earthquake caused major liquefaction damage in San Francisco’s Marina District, which was built on reclaimed land.
- 土壤类型和含水量松散的土壤（如沙子和淤泥）在地震中更容易液化，特别是当它们含水量高时。地下水位高或近期降雨多都会使土壤更加不稳定。例子：2011年新西兰克赖斯特彻奇地震中，潮湿的沙质土壤发生了严重的液化现象。
- 地震强度和震源深度强烈或持续时间长的地震会让地面剧烈摇晃，从而增加液化的可能性。浅源地震会造成更强的地表震动，使液化更严重。例子：1964年日本新潟地震引发大面积土壤液化，导致建筑物倾斜。
- 地理位置和水体附近区域靠近海岸、河岸或填海造地的地区由于地下水位高、土壤松软，更容易发生液化。例子：1989年美国洛马普列塔地震中，旧金山Marina区（填海区域）遭受了严重的液化破坏。
Suggest two physical causes of mass movements generally
- Steep Slopes and Weak RocksGravity pulls material downhill more strongly on steep slopes, increasing the chance of landslides or slumps.Slopes made of weak or loose materials, like clay or soft sediment, are more likely to collapse.If the rocks are layered, especially with water-trapping layers, water can build up and make the slope unstable.Example: On the Dorset Coast (UK), clay-rich cliffs often collapse after rain.
- Heavy RainfallIntense or long periods of rain make the ground heavier and reduce the friction holding it together.Water fills the spaces in soil (pore water pressure) and reduces the soil’s strength, leading to slumps, mudflows, or landslides.Example: In 2010, Pakistan’s floods caused many landslides in mountain areas, displacing thousands of people.
- 陡峭的坡度和弱岩层结构重力在陡坡上更容易将土壤或岩石拉向下方，增加滑坡或塌陷的风险。斜坡如果是由松散或软弱的材料（如粘土或松散沉积物）组成，就更容易崩塌。如果地层是分层的，尤其有不透水层夹在中间，水分就会积聚，降低斜坡稳定性。例子：在英国多塞特海岸，富含粘土的悬崖常因吸水过多而发生滑坡。
- 强降雨和含水量增加连续或强降雨会让土壤吸满水变得更重，同时减少土壤之间的摩擦力。水分会增加孔隙水压力，降低土壤的黏合力，导致滑坡、泥流或碎屑流。例子：在2010年巴基斯坦洪灾期间，山地地区出现了大量滑坡，导致数千人被迫迁移。
Explain why volcanoes can have greater impacts than earthquakes. (7 marks)
- Variety of Hazards from Volcanoes
Volcanoes produce multiple hazards, including:
Lava flows that destroy infrastructure and ecosystems.
Pyroclastic flows that incinerate everything in their path.
Ash fall that disrupts air travel, agriculture, and water supplies.
Lahars (volcanic mudflows) that bury towns under thick layers of debris.
Earthquakes primarily cause ground shaking, which leads to building collapses but has fewer secondary hazards.
Example: The 1991 Mount Pinatubo eruption (Philippines) caused global cooling, ash fall, and lahars that destroyed villages. - Global Environmental and Economic Effects
Large volcanic eruptions inject ash and sulfur dioxide into the atmosphere, leading to climate cooling and agricultural failures.
Example: The 1815 Tambora eruption (Indonesia) caused the “Year Without a Summer”, resulting in global crop failures and famine.
Earthquakes primarily impact local or regional areas, with fewer long-term global consequences. - Duration and Predictability
Earthquakes occur suddenly and last seconds to minutes, whereas volcanic eruptions can last for days, months, or even years.
Example: The Kīlauea eruption (Hawaii, ongoing for decades) continuously reshapes the landscape and disrupts communities.
This prolonged activity means volcanic impacts persist far longer than earthquakes. - Secondary Effects
Volcanic gases (e.g., sulfur dioxide, carbon dioxide) contribute to acid rain, respiratory illnesses, and long-term climate changes.
Landslides and tsunamis triggered by volcanic eruptions can worsen destruction.
Example: The 1883 Krakatoa eruption (Indonesia) generated a massive tsunami, killing 36,000 people.
Suggest reasons for the differences in duration of precursors for various natural hazards e.g. Earthquakes occur suddenly because tectonic stress is released instantly
- Sudden vs. Gradual Hazard Formation
Earthquakes occur suddenly because tectonic stress is released instantly—this makes prediction difficult and means little to no precursors exist.
Volcanoes, hurricanes, and tsunamis develop over time, allowing for precursor detection.
Example: Hurricanes have days to weeks of precursors, while earthquakes may have only seconds of warning. - Detectability and Monitoring
Volcanoes show long-term warning signs (e.g., gas emissions, seismic activity, and ground deformation) before eruption.
Tsunamis have minimal precursors, as they are caused by sudden undersea earthquakes or landslides.
Example: Kīlauea Volcano (Hawaii) had weeks of precursor activity before erupting, while the 2004 Indian Ocean tsunami struck within minutes of an undersea earthquake. - Geographic and Climatic Influences
Hurricanes take time to form over warm ocean waters, allowing meteorologists to track them for days.
Earthquakes are harder to predict because tectonic stress can build for centuries before sudden release.
Example: The San Andreas Fault (California) has built up seismic stress for over a century, but with no major precursor signals.
Explain how pyroclastic flows are formed. (6 marks)
- Column Collapse from an Eruption
During an explosive eruption, a tall column of ash, gas, and tephra is ejected into the atmosphere.
If this column becomes too dense and loses its upward momentum, it collapses, causing material to surge down the volcano’s slopes.
Example: The Mount Pelée eruption (1902, Martinique) produced a pyroclastic flow that destroyed St. Pierre, killing ~30,000 people. - Dome Collapse and Landslides
Some volcanoes form viscous lava domes that block the vent.
When the dome becomes unstable, it collapses under its own weight, generating a hot pyroclastic avalanche.
Example: The Soufrière Hills eruption (Montserrat, 1997) resulted in dome collapse and pyroclastic flows that devastated the island’s capital. - Lateral Blasts from Explosive Eruptions
Occasionally, a sideways explosion occurs instead of a vertical eruption, sending pyroclastic material outward at high speeds.
Example: The Mount St. Helens eruption (1980, USA) caused a massive lateral blast, producing a deadly pyroclastic surge that flattened forests and killed wildlife.
Explain the formation of a tsunami (6 marks)
- Submarine Earthquake and Water Displacement
A megathrust earthquake occurs at a subduction zone, where one tectonic plate is forced beneath another.
The seafloor is suddenly displaced, causing a massive upward push of water.
This displacement creates a series of waves that radiate outward in all directions from the epicenter. - Wave Propagation Across the Ocean
The displaced water generates waves that spread outward in all directions at speeds of up to 800 km/h in deep water.
In deep water, tsunami waves have long wavelengths (100–200 km) and low wave heights (~1 m), making them difficult to detect.
As the waves travel across the ocean, they maintain their energy over long distances. - Shoaling Effect and Coastal Impact
As the tsunami waves approach shallow water, friction with the seabed slows them down, causing the waves to increase in height.
Water often withdraws from the shore before the tsunami arrives, exposing the seabed—a key warning sign.
The tsunami then surges inland, causing widespread destruction.
Example:
The 2011 Tōhoku Earthquake and Tsunami off the coast of Japan caused massive devastation, with waves reaching 40 meters in some areas.
Explain two factors that influence the height of a tsunami on reaching a coastline. (6 marks)
- Water Depth and Seafloor Gradient
In deep water, tsunami waves have a long wavelength and low height, traveling at speeds of up to 800 km/h.
As the wave enters shallower water, friction with the seafloor slows it down, causing wave height to increase—a process known as shoaling.
Steep offshore slopes lead to smaller tsunami heights, while shallow coastal shelves allow for higher waves.
Example: The 2004 Indian Ocean tsunami had devastating impacts on flat coastal areas in Indonesia, Sri Lanka, and Thailand, where waves exceeded 30 meters in height. - Coastal Shape and Orientation
Bays and inlets can funnel tsunami waves, increasing their height and amplifying destructive power.
Coasts directly facing the tsunami’s direction experience higher waves, while islands or headlands may block some energy, reducing impact.
Example: In the 2011 Tōhoku tsunami (Japan), waves were higher in narrow coastal inlets, where they reached up to 40 meters due to wave focusing.
Explain how volcanic hazards may be related to the type of volcanic eruption. (6 marks)
- Effusive Eruptions (Shield Volcanoes)
These eruptions produce low-viscosity, basaltic lava, which flows easily and over long distances.
Main hazards:
Lava flows, which can destroy infrastructure but move slowly, allowing evacuation.
Gas emissions (e.g., sulfur dioxide), which can cause air pollution and respiratory issues.
Example: The Kīlauea volcano (Hawaii) continuously erupts basaltic lava, threatening roads and homes. - Explosive Eruptions (Stratovolcanoes)
These eruptions produce high-viscosity, silica-rich magma, which traps gas, leading to violent explosions.
Main hazards:
Pyroclastic flows (fast-moving clouds of hot gas and ash) that incinerate everything in their path.
Lahars (volcanic mudflows) caused by ash mixing with rain or melted snow.
Ash fall that disrupts air travel and agriculture.
Example: The Mount St. Helens eruption (1980) produced pyroclastic flows and a massive lateral blast. - Phreatomagmatic Eruptions (Water-Magma Interaction)
When magma contacts water, it causes steam explosions, triggering violent eruptions and tsunamis.
Example: The 1883 Krakatoa eruption (Indonesia) triggered a tsunami that killed 36,000 people
