Geo 201 Today LO) To be able to describe the characteristics of a lahar SC) You can describe a lahar and how it is different to a flood DN) Login and make sure you have your 2B5

What is a Lahar? And what sort of damage can it do? After During

Flood vs Lahar

Why do we need to know? “Mt Ruapehu is predicted to erupt within the next few years. The Ministry of Civil Defence and Emergency Management (CDEM) has asked that you prepare an up to date lahar risk analysis for the surrounding area. While an eruption causes many risks, the CDEM requires you only to analyse the risks caused by lahars from the eruption. “ - From your Task Booklet

So What is the CDEM? Section of Civil Defence Responsible for mitigating Natural hazards like Lahars To get technical… Co-ordinate all planning activities related to hazard and emergency management Examine the risks that hazards may pose to the goals, and prioritise each hazard.

2007 Ruapehu Lahar on Whakapapa Ski Field

Images from a Horizons Webcam (Ruapehu Lahar)

Mt St Helens, USA

Look Familiar…?

Lahars - Background - Causes - Mitigation Lahars

Background A type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water from a volcano "Lahar" is a Javaneve word that describes volcanic mudflows or debris flows Lahars have the consistency, viscosity and approximate density of concrete: fluid when moving, solid at rest Responsible for 17% of volcano-related deaths

Causes of Lahars Lava flow out of open vents can mix with wet soil, and mud on the slope of the volcano making a very viscous, high energy lahar. (The higher up the slope of the volcano the more energy the flow will have) Snow and glaciers can be melted by lava or pyroclastic flows during an eruption. A flood caused by a glacier, lake breakout, or heavy rainfall can release a lahar Water from a crater lake, combined with volcanic material in an eruption

Lahars at Ruapehu Mt Ruapehu is considered particularly dangerous due to the risk of lahars. A lahar warning system has been set up at Mount Ruapehu by the Department of Conservation and hailed as a success after it successfully alerted officials to an impending lahar on 18 March 2007

Class Brainstorm What might we be able to do to mitigate the effects of a lahar on the natural and cultural environment?

Mitigation Strategies Class brainstorm What might we be able to do to mitigate the effects of a lahar on the natural and cultural environment? Order thi Use dynamite to bomb the crater lake to release lahars before they become potentially large and uncontrollable Isolate the lahar area (what do we mean by this?) Raise the bridges and reinforce them Stop banks constructed Develop warning system Artificial levees Build a fence/barrier using steel and concrete Relocate the ski fields Stop/reduce human activity (needs to be specific) Create a deep trench to ‘catch’ the lahar

Task Go to flood-control-structures/ (or Google “prezi lahar flood control structures”) flood-control-structures/ Full-screen it and navigate using the L/R arrows Flick through the Prezi and use it to answer the questions on the hand out titled: Lahar and Flood Control Structures OR Complete the answers in your 2B5 in full sentences from the TV screen (next slide) You have 15 minutes to complete this task

Task Questions 1.Where does a lahar originate from? 2.What are the 2 main causes of floods? 3.What might the term ‘watershed’ mean? 4.Briefly describe how a bund is created 5.What might ‘undermining’ mean and how might a Groyne prevent it? 6.What might be another term for a levee? 7.Why would a flood wall cost more to construct than a levee? (imagine they are both the same length) 8.What would be more damaging – a flood or lahar if they both had the same volume/flow rate?

Geo 201 Today LO) To be able to describe what has been done on Ruapehu to mitigate Lahars SC) You can describe lahar mitigation projects around Mt Ruapehu DN) Take 10 minutes to complete the questions from yesterday (Google “prezi lahar flood control structures”)

Our Context 1.Mount Ruapehu Crater Lake 2.All rivers that lead down from this lake are potential lahar paths 3.Traditionally, the Whangaehu River carries lahars (Tangiwai disaster happened here)

You will be proposing mitigation strategies to the CDEM You must therefore know what is already in place so that the suggestions are realistic So writing in a report that suggests things that have already been done is a waste of time! So that we will not waste anyone’s time.. What has already been done?

So what has been done already? You will be proposing mitigation strategies to the CDEM in 2014 You must therefore know what is already in place so that the suggestions are realistic So writing in a report that suggests things that have already been done is a waste of time! But we can still suggest they be improved

Task – Lahar Mitigation Summary 1.Open the folder S:\Social Science\2. Geography\GEO 201\2014\Spatial Analysis\Ruapehu Lahars Info for today’s resources (3 documents) 2.Create a Doc called “Ruapehu Lahar Mitigation” 3.Use the resources to research at least 2 things that have already been done to mitigate the effects of a lahar in the Whangaehu River 4.Complete a summary table like this one: What did they do exactly? Why did they do it (how will it mitigate?) How much did it cost? Do you think it could be modified or improved?

Tips for the Task When looking at a resource, read the subheadings first to see what section you want. Eg “background” or “Introduction” Have Google Earth open as well so you can get an appreciation for where everything is and what it looks like (such as the Whangaehu River) You will use this information in the assessment, so get a head start now