Tsunami
Chch’s tsunami hazards
Christchurch has tsunami hazards mainly because it sits on the east coast of the South Island, facing the Pacific Ocean. People who live, work, or visit areas close to the shore, such as New Brighton, Sumner, Redcliffs, Southshore, and the lower parts of the Avon and Heathcote rivers, are most at risk because these places are low lying and close to the water. A tsunami affecting Christchurch would likely come from a large offshore earthquake in places like the Hikurangi Subduction Zone near the North Island, or from distant places such as South America across the Pacific Ocean. To be prepared, people should know their closest tsunami evacuation zone, practise walking to higher ground, have an emergency kit ready, and leave immediately if they feel a long or strong earthquake. Staying informed through alerts, maps, and local emergency services is also important so that people can react quickly and stay safe.
Volcanos
What are the six types of volcanic eruption?
There are six main types of volcanic eruptions and each one behaves differently. A Hawaiian eruption is gentle and named after the volcanoes in Hawaii because it releases runny lava that flows easily across the ground. A Strombolian eruption is named after Stromboli in Italy and has small but regular bursts of lava that shoot into the air. A Vulcanian eruption is named after the island Vulcano and is stronger, sending ash, gas and rocks high into the sky. A Pelean eruption is named after Mount Pelee in the Caribbean and creates deadly pyroclastic flows that rush down the volcano at high speed. A Plinian eruption is named after Pliny the Younger who recorded the eruption of Mount Vesuvius, and these eruptions send massive ash clouds high into the atmosphere. The final type is a Surtseyan eruption, named after the island Surtsey in Iceland, and it occurs when lava and water meet, creating steam explosions. Each type can be seen in real volcanoes around the world, such as Kilauea in Hawaii or Mount Vesuvius in Italy.
What are the main types or shapes of volcano?
The three main shapes of volcano are shield volcanoes, composite volcanoes, and cinder cone volcanoes. Shield volcanoes have wide, gentle slopes because they are formed by runny lava that travels far before cooling, and Hawaii has many examples of this shape. Composite volcanoes are tall, steep and dangerous because they are built from layers of ash and lava, and examples include Mount Fuji in Japan or Mount Ruapehu in New Zealand. Cinder cone volcanoes are small and steep with a simple cone shape built from volcanic rock fragments that fall back around the vent. These shapes form depending on the type of lava, how often the volcano erupts, and the style of eruption.
Explosive and effusive eruptions and lava types
Explosive eruptions happen when thick lava traps gas inside the volcano until it bursts violently, sending ash, rocks, and gas into the air. This thick lava is called andesite or rhyolite and it cools into rough, sharp rocks and large ash layers. Effusive eruptions are calmer because the lava is thin and runny, which allows gas to escape easily. This lava is mostly basalt and it forms smooth lava flows that spread across wide areas. These different lavas create very different landscapes because explosive eruptions build steep volcanoes with ash and rock layers, while effusive eruptions build wide volcanoes with long lava flows.
What agencies deal with hazards and disasters in New Zealand?
New Zealand has several agencies that help with hazards and disasters to keep people safe. The National Emergency Management Agency leads the country’s disaster planning and gives instructions during emergencies. GeoNet studies earthquakes, volcanoes, tsunamis and landslides and provides warnings and scientific information. Fire and Emergency New Zealand helps with rescues, fires, floods and other emergencies. Local councils prepare evacuation zones, warnings and community plans so people know what to do.
Difference between a lahar, landslide, mudflow and pyroclastic flow
A lahar is a fast moving flow of volcanic mud and water that comes from a volcano when ash mixes with rain, melted snow or lake water. A landslide is when a large amount of rock or earth suddenly slips down a slope usually after heavy rain or shaking from an earthquake. A mudflow is similar but contains more water and moves like thick liquid down valleys. A pyroclastic flow is the most dangerous because it is a burning cloud of ash, gas and volcanic rock that rushes down a volcano at very high speed. Lahars happened on Mount Ruapehu in New Zealand, deadly landslides have occurred in places like Kaikoura, mudflows often follow storms on steep hills, and pyroclastic flows destroyed towns during the eruption of Mount Pelee.
Analyse a disaster movie event
Many disaster movies show volcanic eruptions that are exaggerated or unrealistic to make the story exciting. For example, some films show characters outrunning a pyroclastic flow or lava moving extremely fast, which is not possible in real life because pyroclastic flows move faster than cars and lava usually moves slowly but is extremely hot. Movies also often show eruptions happening suddenly with no warning, but in real life scientists usually detect signs like earthquakes, gas changes, or ground movement. While movies can be entertaining, many scenes are not realistic because they ignore real volcanic behaviour and safety rules to create drama.