Reader response draft 3
In the article, “How Volcanic Ash Strengthens a Roof Against
Powerful Projectiles,” Williams (2019) proposes that having a layer of volcanic
ash on the rooftops of building can increase protection from volcanic
projectiles. He mentions that a study by scientists from the Earth Observatory
of Singapore (EOS) and the University of Canterbury (UC) was conducted to
measure the ability of ash to cushion volcanic projectile impacts shot by a
high-pressure air cannon, in which tests show that having a five centimeters
ash layer tripled the strength of the roof to withstand projectiles. He notes
that while a thicker layer helps, it increases the risk of the roof collapsing.
He states that scientists also believed that buildings would be more damaged
when struck by multiple projectiles compared to one. However, the tests proved
otherwise, provided that the roof is protected with a 5 cm layer of tephra.
Nonetheless, he remarks that this method should be done on an individual basis
by ensuring the shelter benefits from the tephra on its roof, and still
withstand its weight. Therefore, he concludes buildings with reinforced
concrete roofs are found to be ideal.
Although this is a fine discovery and can be beneficial against
volcanic projectiles, the advantage provided is negligible compared to the other
dangers a house may face in an event of a volcanic eruption.
Firstly, having a layer of 5cm of ash on the roof is a good idea
by itself, as it can help protect the house from volcanic projectiles. However,
it inevitably has the risk of overloading the roof. A volcanic eruption will
release volcanic ash and this will pile onto the roofs, which will further increase
the risk of roof collapse. Yamamoto et al. (2016) mentions that the
ash from the Mount Ontake eruption could be a danger to the houses nearby the
eruption if a large amount of ash was collected by the roof of a house. Hence, many
houses had ash deposited onto their rooftops from the Mount Ontake eruption. If
the houses were to have the protective layer of ash in its roofs, the weight
from the additional ash would significantly increase the risk of the building
collapsing.
Secondly, ordinary roofs have already shown that they can put up
some resistance and not just crumble when being hit by volcanic projectiles.
Therefore, it is not crucial for this protective layer to be implemented.
Ballance (2017) writes about an experiment, done by the same team from the
University of Canterbury previously, examining if typical roofs were able to
withstand volcanic projectiles. The test revealed that for concrete roofs, the
projectile was able to penetrate through it, but it was stopped by the metal
reinforcing rods in the concrete. It can be concluded that concrete roofs are
good enough to withstand projectiles and protect its occupants, so long as it
has something on the bottom side to prevent the broken pieces of concrete
caused by the projectile impact from potentially causing more damage.
Finally, the protection the layer provides seems minuscule
compared to the other dangers a house may face in a volcanic eruption.
Projectiles can be massive, making the protection layer useless, and they are
not even the only concern. Cain (2009) states about the dangers of volcanoes
depending on the size of an eruption. Houses nearby have almost no chance
against its dangers, ranging from the slow but extreme force and heat of a lava
flow, to pyroclastic flows, when scorching hot rock and gas travel down the
volcano at a speed greater than 700km/h, traveling far distances and
annihilating everything in its way. Even huge boulders have been known to be
shot several kilometers away, which would destroy a house even with the
protective layer.
In conclusion, it is fundamental that more research needs to be done
to work together with this finding, such as how to prevent the roof from collecting volcanic ash in the event of an eruption.
References
Balance, A. (2017). Will your roof withstand flying volcanic rocks? Our changing world.
Balance, A. (2017). Will your roof withstand flying volcanic rocks? Our changing world.
https://www.rnz.co.nz/national/programmes/ourchangingworld/audio/201847343/will-your-roof-withstand-flying-volcanic-rocks
Cain, F. (2009, April 22). Volcano dangers. Universe today.
Williams, G. (2019, November 12). How volcanic ash strengthens a roof against powerful projectiles. Earth observatory blog.
Yamamoto, T., Inoue, M. (2016). A study on sliding characteristic of volcanic ash deposited on pitched roofs of wooden houses. Journal of structural and construction engineering (Transactions of AIJ), 81(724):959-969. https://www.researchgate.net/publication/304612578_A_Study_on_sliding_characteristic_of_volcanic_ash_deposited_on_pitched_roofs_of_wooden_houses
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