Lahars

Lahars are fast flowing, destructive mud-rock slurries. They can occur at any time, and happen very fast, so getting to safe ground is crucial.

Considered to be deadlier than the eruption of the volcano itself, Lahars are a topic on which most people aren't educated on. Lahars cause major economic and environmental damage. Lahars of a large enough degree can easily crush, abrade, bury, or carry away most things that stand in their way. When they strike building and valuable land, they can partially or fully bury them depending on the magnitude of the lahar. If you aren't prepared and live in an area that is prone to lahars and one were to happen, the chances of you surviving would be low due to how far they can travel (up to 300km) and at crazy fast speeds (200km/h).

One deadliest Lahars that was recorded in recent history has to Nevado Del Ruiz Lahar. In 1985 the lahar in this region passed through the town of Armero, Colombia wiping and submerging everything in it's path and took the lives of 21,000 people. Ineffective evacuation after warning messages are broadcast, poor emergency response, and a haphazard disaster recovery are all factors of why this Lahar was so deadly, when a lot of this could have been avoided if the people of that region were properly educated and had escape routes, etc. ready to be able to fall back on at any time. Other factors also include: evacuation plans that had been prepared but not shared with the public, poorly equipped emergency management authorities, the absence of agreed-upon decision-making processes, and uncertainty about the pre-event hazard assessments that made public officials reluctant to issue an early evacuation order because of the potential economic and political costs. Weirdly enough the hazard maps that were created by scientists were highly accurate on where the lahars could potentially divert, but due to potential economical and political costs was issued late and didn't give locals enough to to assess the situation.

As show in this image they are using timber logs in a fence like manner to contain the soil and stabilize this steep slope. Slope stabilization is usually needed in places with volcanic activity. This is due to the fact that after a volcanic eruption, the slopes around the volcano get covered in a blanket of ash, this causes the soil to be extremely vulnerable to rapid surface erosion and shallow landsliding. The soil will easily shift if hit by a lahar. Even after long periods of time this ash covered soil can easily give out, even through the long natural processes of soil restoration. These slopes giving can cause catastrophic damages. Various methods of slope stabilization, slope protection, and erosion control can limit shallow landsliding or surface erosion in disturbed landscapes. But, these methods are usually the ones that are costly and intensive.

Examples of Slope Stabilization include:

Rock, synthetic polymers, wood, steel, reinforced concrete

As you would think, most of these methods do tend to degrade over time.

The reason that these methods are effective would be because they stiffen and hold the ground together, not letting it move if natural forces start to act on it. Since the movement of soil/ground is the main issue when it comes to a lahar getting bigger. As we know lahars get bigger by basically taking all the loose material along with it while it's on it's destructive course.

The clear answer for the stakeholder responsible for this solution would have to be the government. They for sure have the funding and are the ones responsible for the safety of the people who reside in that country. When saying this in more detail, not the federal government, but a local level of government (ex. Ontario Gov, not the Canadian Gov.) have to be the ones to put these

This method is quite simply put, the most simple. As you can infer from the name, they are structures that divert the lahar stream. These diversion structures are designed to redirect/reroute away and around important infrastructure or communities. Example a) shows how engineers built a channel to redirect water from a small river near the Sakurajima volcano in southern Japan, where channel is revetted with reinforced concrete and engineered to be as steep, narrow, and smooth as possible, in order to divert lahars away from a developed area. Example b) shows reinforced metal "walls" to help direct the downhill flow of water, and lahars when needed. I areas that are highly prone to strong lahars, deeper "dikes" can be dug to accombinate the larger magnitude.

As mentioned earlier these dikes can be very flexible depending on the location (If it is near a bigger volcano they can be made deeper, and vise versa to accombinate the scale of the lahars that could occur in that area). They can also be incorporated straight into nature and won't disrupt much in their surroundings. The stakeholders would be the same as the previous solution due to it being a job of construction that would require knowledge of the areas that the lahars would flow through, so that you

These structures help prevent lahars from going down and reaching further downstream. They are great at sealing off and protecting areas that would otherwise be hit hard by a lahar (sensitive areas that might include electrical stations, oil storage facilities, airstrips, and some buildings). Structures trying to contain lahars must have enough storage to prevent overtopping. Example a) shows a Sediment Retention Structure (SRS), which was built for the soul purpose of to contain potential lahars and eroded sediment. Example b) shows a dam with a large concrete overflow spillway. Designed for flood control, they also had the thoughts of it being a trap for lahars in the future. Examples c) shows exclusion levees surrounding the Drift Oil Terminal that is located on an alluvial plain. It is located 40km downhill from the Redoubt Volcano in Alaska. All these methods are very effective because they take place on such a large scale. Since lahars need loose sediment to grow and get bigger, all these methods either hold back as much sediment or divert it away from important infrastructure. Also, having structures that are made up of concrete allows for the lahar to not get any bigger and allows for better containment. Concrete is also great because it is a material that doesn't erode, which is perfect for any structure that wants to be able to contain a lahar. Just like the previous two solutions this needs to be handled by more local authorities and not on the federal level. People who have a good understanding of the area and this form of disasters, should in theory be the ones who have to execute these structures, while also getting help from professionals from others fields to plan and and build them.

To conclude. Instead of trying to save people and give them evacuation procedures, stopping, diverting, and containing the lahars before they reach communities in my opinion is the best route to take. Stopping them at the source (saying that dramatically, meaning that you stop them early on instead of paying the price later. If something does end up going wrong, these safety protocols and evacuation procedures are there as a plan b.

Andrews, R. (2018, February 03). This Is How Volcanoes Can Kill You After They've Finished Erupting. Retrieved January 06, 2021, from  https://www.forbes.com/sites/robinandrews/2017/05/20/this-is-how-volcanoes-can-kill-you-after-theyve-finished-erupting/?sh=fb2901115b2b 

Pierson, T. C., Wood, N. J., & Driedger, C. L. (2014, September 06). Reducing risk from lahar hazards: Concepts, case studies, and roles for scientists. Retrieved January 07, 2021, from  https://appliedvolc.biomedcentral.com/articles/10.1186/s13617-014-0016-4 

Riley, C. M. (n.d.). Lahars. Retrieved January 06, 2021, from  http://www.geo.mtu.edu/volcanoes/hazards/primer/lahar.html 

Only 3 sources because the 1st one had almost everything (The article is around 25 pages, and has many authors)