Query: While volcanic eruptions are natural events, it was the timing of these that had such a noticeable effect on the trend

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Nuclear winter <=SEP=> Nuclear winter is the severe global-climatic-cooling-effect , hypothesized to occur after the ignition of a number of firestorms , from nuclear bomb detonations , or wide spread bombardments . Such fires , which can inject soot into the stratosphere , have historically occurred in a number of cities , with nuclear winter researchers using both Hamburg and the less ferocious Hiroshima firestorms as the principal examples . However , as firestorms are most frequently encountered in much larger area wildfires , these latter fires are the most significant today in assessing both the initial and present-day `` nuclear winter '' computer models .

1257 Samalas eruption <=SEP=> The 1257 Samalas eruption was a major volcanic eruption of the Samalas volcano , next to Mount Rinjani on the island of Lombok , Indonesia . It left a large caldera next to Rinjani volcano , the lake Segara Anak . This volcanic eruption reached a volcanic explosivity index of 7 , making it one of the largest eruptions of the Holocene . The occurrence of this eruption was originally deduced from ice core information revealing a spike in sulfate deposition around the year 1257 ; in 2013 the source of this eruption at Samalas was definitively proven as a result of historical records from that time .   This eruption proceeded during four distinct phases , alternately creating eruption columns reaching up for tens of kilometres and pyroclastic flows that buried large parts of Lombok , destroying human habitations including the city of Pamatan . Ash from the eruption fell as far as Java . The volume of the deposits left exceeds 10 km3 . Later activity from the volcano created additional volcanic centres in the caldera , including the present day active Barujari cone .   The eruption was witnessed by humans on Lombok , who recorded its effects on text written on palm leaves . The aerosols injected by the volcano into the atmosphere reduced the solar radiation reaching the surface of the Earth , triggering a volcanic winter and cooling lasting for several years . It is possible that the 1257 Samalas eruption helped trigger the Little Ice Age .

Natural disaster <=SEP=> A natural disaster is a major adverse event resulting from natural processes of the Earth ; examples include floods , hurricanes , tornadoes , volcanic eruptions , earthquakes , tsunamis , and other geologic processes . A natural disaster can cause loss of life or property damage , and typically leaves some economic damage in its wake , the severity of which depends on the affected population 's resilience , or ability to recover and also on the infrastructure available .   An adverse event will not rise to the level of a disaster if it occurs in an area without vulnerable population . In a vulnerable area , however , such as Nepal during the 2015 earthquake , an earthquake can have disastrous consequences and leave lasting damage , requiring years to repair .

Volcano <=SEP=> A volcano is a rupture in the crust of a planetary-mass object , such as Earth , that allows hot lava , volcanic ash , and gases to escape from a magma chamber below the surface .   Earth 's volcanoes occur because its crust is broken into 17 major , rigid tectonic plates that float on a hotter , softer layer in its mantle . Therefore , on Earth , volcanoes are generally found where tectonic plates are diverging or converging , and most are found underwater . For example , a mid-oceanic ridge , such as the Mid-Atlantic Ridge , has volcanoes caused by divergent tectonic plates pulling apart ; the Pacific Ring of Fire has volcanoes caused by convergent tectonic plates coming together . Volcanoes can also form where there is stretching and thinning of the crust 's , e.g. , in the East African Rift and the Wells Gray-Clearwater volcanic field and Rio Grande Rift in North America . This type of volcanism falls under the umbrella of `` plate hypothesis '' volcanism . Volcanism away from plate boundaries has also been explained as mantle plumes . These so-called `` hotspots '' , for example Hawaii , are postulated to arise from upwelling diapirs with magma from the core -- mantle boundary , 3,000 km deep in the Earth . Volcanoes are usually not created where two tectonic plates slide past one another .   Erupting volcanoes can pose many hazards , not only in the immediate vicinity of the eruption . One such hazard is that volcanic ash can be a threat to aircraft , in particular those with jet engines where ash particles can be melted by the high operating temperature ; the melted particles then adhere to the turbine blades and alter their shape , disrupting the operation of the turbine . Large eruptions can affect temperature as ash and droplets of sulfuric acid obscure the sun and cool the Earth 's lower atmosphere ( or troposphere ) ; however , they also absorb heat radiated up from the Earth , thereby warming the upper atmosphere ( or stratosphere ) . Historically , so-called volcanic winters have caused catastrophic famines .

Volcanism <=SEP=> Volcanism is the phenomenon of eruption of molten rock ( magma ) onto the surface of the Earth or a solid-surface planet or moon , where lava , pyroclastics and volcanic gases erupt through a break in the surface called a vent . It includes all phenomena resulting from and causing magma within the crust or mantle of the body , to rise through the crust and form volcanic rocks on the surface .