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Which are most hazardous, destructive or conservative boundaries? From the Andes to the Himalayas, Plate boundaries are famed for the astounding formed around them and have become geological and tourist hotspots. However constant lithospheric movement plate boundaries pose an extreme hazard when in contact with human populations, damaging economies and communities. Plates move in varying ways, while at conservative boundaries parallel plates slide past each other; convergent (or destructive) margins are characterised by one plate subducted under another. The magnitude and frequency of volcanism and seismic activity at each margin discerns the relative hazards they pose; yet the global distribution is also a critical factor in the dangers carried. One of the most hazardous features at plate boundaries are volcanoes where magma extrudes to the surface. As conservative boundaries do not feature any crustal subduction or creation- as destructive margins do- they are undoubtedly less hazardous in this sense. Meanwhile at destructive margins where continental crust collides with oceanic, or two oceanic plates meet, volcanoes are prevalent features. This is visible across the globe with major volcanoes like Krakatoa and Mount Etna both created as denser crust-of 3g/cm2 – is subducted under more buoyant continental crust, melting into the mantle. The less dense magma now rises through the crust, emerging as a volcano. Volcanism at destructive boundaries are some of the most perilous as highly viscous andesitic and rhyolite lava is produced, catalysing huge and powerful eruptions. This was witnessed at Mount Etna in 1992 where pyroclastic flow reached the village of Zafferana, over 7km away. In addition the strombolian and convex shape of destructive boundaries-like Vesuvius- holds the further hazard of flank collapse. With steep sides avalanches similar to which engulfed Valle De Bove after Etna’s 1928 eruption can destroy adjacent communication links, hindering evacuation and rescue efforts. When mount Chaiten erupted in 2008, local industry took 5 years to return to 2007 levels, forcing 30% of the male population to migrate to surrounding cities. Consequently destructive margin volcanoes potentially hold more danger that the Icelandic shapes on constructive boundaries. Hazards are also enhanced when populations are pushed out of their zone of tolerance; two similar magnitude volcanoes may have differential impacts, depending on the capacity to respond. The lack of frequency of volcanoes at destructive boundaries means many authorities are not prepared for the impact of lava flows, Lahars and pyroclastic flow. As the 19 fatalities during Soufriere hills eruption in Montserrat exhibits, mitigation was not implemented and residents were not accustomed to dealing with such hazards. In comparison to Hawaiian authorities, adapted to Mauna Loa’s continual eruption, Montserrat’s government was not prepared for the eruption injecting a mere $30,000 was in evacuation projects. In addition due to the 60% silica rich soil neighbouring volcanoes agricultural industries have traditionally been attracted here. Today these areas are densely populated, on Java over 120million live in the shadow of 30 volcanoes. This is an increasing concern following mount Sinabung’s eruption earlier this month where over 40,000 residents need to be evacuated to comprehensively ensure survival. Furthermore the Indonesian government cannot afford to divert Lava flows as Icelandic authorities did in the 1974 Heimaey eruption. Indeed geologists at Naples University warn that despite building regulations introduced in 1995, should Vesuvius erupt again, only 5% of the city’s population would be successfully evacuated. Both substantial populations and the significant lethal features at Convergent margin volcanism enhance the social and economic hazards posed. Regardless of the lack of volcanic activity at Conservative boundaries, convergent margins independently pose immense threats. Furthermore gases emitted from pressure release when magma rises to the surface can extend the hazard posed from a local scale to global reverberations. As destructive margins contain Rhyolite magma, volcanoes along this margin emit potent gases like Sulphur Dioxide, CO2 and Carbon monoxide, as Krakatoa did in 1883- when injection of sulphur dioxide into the Atmosphere caused temperatures to plummet by 1.2 o. However these remain isolated events and debate remains over the actual impact of volcanically emitted gases. Compared to 35 bn tons of anthropogenic CO2 produced per year, the 0.44 Gigatons from volcanic movement is dwarfed. Consequently the long term atmospheric hazard posed by volcanoes significantly less than human induced dangers; generating scepticism over the potency of volcanic climate change. Yet volcanism is not the sole measure of hazard posed by a plate margin, seismicity also holds major dangers. Here conservative plate margins rival the threat posed at destructive margins. Pressure release from the friction of two parallel plates sliding past each other can instigate large tremors like in Haiti in 2004 and Turkey 1999, with both quakes reached 7 on the Richter scale. This happens often around the immensely active San-Andreas fault line where the pacific and North American plates migrate north at 6cm pa and 1cm pa respectively. The epicentres of these quakes are relatively shallow- only 10km deep in Haiti 2004- creating more powerful surface waves. In comparison to deeper epicentres at destructive margins these waves pose a far greater hazard to human life. Bolivia’s 1994 quake exposes this, despite reaching 6 on the Richter scale; only 1000 homes were damaged in comparison to the 1999 Anatolian fault quake where over 50,000 Turkish residences were damaged. Lower epicentres (or Benioff zones) at destructive boundaries are caused by the compression of crust being subducted deep into the lithosphere, as seen along Japan’s coast where the Eurasian plate is subducted at 40O. Despite variations in tremor waves converging margins have equally damaging potential, and the hazardous nature of destructive boundaries cannot be overlooked. Indeed the biggest earthquake ever recorded – in Chile 1960- occurred where the Nazca plate meets the South American, reaching a staggering 9.5 in magnitude. Conclusively, though quakes at these margins differ in magnitude and formation, they pose equally fatal hazards to surrounding communities. Despite varying magnitudes produced by the physics at each boundary, it could be argued that it the prime determinant for the scale of hazard posed is in fact the location of the Earthquake. A seismic tremor in a highly populated area will undoubtedly cause more social and economic damage than those in isolated regions. Consequently destructive boundaries could be considered far more hazardous, as my diagram shows, subduction zones straddle densely populated regions including New Zealand and Indonesia, contiguous to Japan’s coastline. By comparison over 70% of Conservative boundaries are located in the oceans, across the Atlantic and south pacific. Thus, while the movement between the Pacific plate and the Honushu in 2011 killed 15,000 and destroyed over 120,000 buildings, the same magnitude quake at a transform margin in the Mid-Atlantic earlier this month went largely unobserved. In addition lower economic development can also exacerbate the hazard posed by earthquake events. Many LEDC countries cannot afford to construct quake resistant buildings, with over 80% of casualties stemming from building collapse; fatalities are likely to be far higher. Compared to conservative boundaries like the San- Andreas fault in California where GDP is $1.8 trillion, destructive boundaries are largely near less developed regions like the Philippines and Indonesia with GDPs half this figure at $500bn and $830bn respectively. The dramatic disparity between the Loama Prieta quake in 1989 and in the Philippines in 2013 highlights the relative hazard to human life. With over 60% of housing constructed illegally and only the capital Manila boasting steel re-enforcements for buildings, there were over 5,000 estimated deaths, a stark contrast to San- Francisco where only 63 died. Here California state council invested over $2bn in pendulums and steel cores making the city far more resistant to seismic hazard. Yet it could be argued that the risk of collapse in MEDCs is a greater economic risk. Hosting 30% of west coast trade, the Pacific Exchange base and 2,800 international technology companies, destruction in San-Francisco would have global repercussions, unlike the strike on Tacloban (Philippines 2013) where global stock markets did not move. By comparing Haiti and San-Francisco’s quake the effect of development is palpable. Despite both occurring on conservative margins at similar magnitudes, the 316,000 Haitian deaths in contrast to San-Francisco’s mere 63 exposes how expert infrastructure and resources to combat secondary diseases can dramatically reduce seismic hazard, irrespective of plate boundary movement. The frequent isolated or economically developed locations of many Conservative boundaries, suggests that Earthquake activity is significantly less hazardous to human activity than their convergent counterparts. In addition due to rapid improvements in seismic prediction technology, the hazard posed by conservative boundaries may begin to reduce in the future. This is crucial as unlike volcanic events, Earthquakes are sudden impact hazard. With improved forewarning systems evacuation procedures can be instigated; pivotal to reducing human fatalities. Improvement has been seen along the Anatolian fault, where in 1999 the quake was in fact successfully predicted using radon gas sensors. Doubly the San-Andrea’s fault has 5 seismic research centres along the line, where by tracking plate movement researchers at USGS have produced ‘Deterministic and Scenario Ground-Motion Maps’; the slower onset enabling emergency response units to conduct training exercises based on realistic earthquake situations. Although this potentially reduces the relative hazard at conservative boundaries in comparison to continued ambiguity at destructive margins, effectively coordinated evacuation is still demanded. Judging by Turkey’s 1999 failure to respond leaving 17,000 dead, this continues to demand improvement. Undoubtedly lack of volcanic activity as Conservative margins means Converging boundaries are the obvious volcanic risk. Yet Seismicity is an equally potent hazard and the difficulty in mitigating and responding to Earthquake events makes them fatally dangerous to those affected. However as both margin formations create equally large quakes; their relative locations determine the extent and significance of the hazard posed. Despite catastrophic Conservative boundary quakes like Haiti, due to the predominantly less developed and more densely populated locations along destructive margins, these unquestionably carry greater long and short term, social and economic hazards.