1815 eruption of Mount Tambora
|1815 eruption of Mount Tambora|
|Location||Sumbawa, Lesser Sunda Islands, Dutch East Indies
|Impact||Reduced global temperatures, leading the following year, 1816, to be called the Year Without a Summer.|
The 1815 eruption of Mount Tambora was one of the most powerful in recorded history and classified as a VEI-7 event. Mount Tambora is on the island of Sumbawa in Indonesia. The eruption that began on 10 April 1815 was followed by between six months and three years of increased steaming and small phreatic eruptions. The eruption column lowered global temperatures, and some experts believe this led to global cooling and worldwide harvest failures, sometimes known as the Year Without a Summer.
Disruption of global temperatures
The conditions during the northern hemisphere summer of 1816 were the result of the largest observed eruption in recorded human history, one during which global temperatures decreased by an average of 0.53 °C, and related human deaths were reported to be about 90,000. The importance of volcanic eruptions during this anomaly, specifically the eruption of Mount Tambora, cannot be overlooked. It is the most significant factor in this important climate anomaly across the globe (Robock 2000). While there were other eruptions during the year of 1815, Tambora is classified as a VEI-7 and an eruption column 45 km tall, eclipsing all others by at least one order of magnitude.
The Volcanic Explosivity Index (VEI) is used to quantify the amount of ejected material with a VEI-7 coming in at 100 km3. Every index value below that is one order of magnitude less. Furthermore, the 1815 eruption occurred during a Dalton Minimum, a period of unusually low solar radiation (Auchmann et al. 2012). Volcanism plays a large role in climate shifts, both locally and globally. This was not always understood and did not enter scientific circles as fact until Krakatau erupted in 1883 and tinted the skies orange (Robock 2000).
The scale of the volcanic eruption will determine the significance of the impact on climate and other chemical processes, but a change will be measured even in the most local of environments. When volcanoes erupt they eject CO2, H2O, H2, SO2, HCl, HF, and many other gases (Meronen et al. 2012). CO2 and H2O are greenhouse gases, responsible for 0.0394% and 0.4% of the atmosphere respectively. Their small ratio disguises their significant role in trapping solar insolation and reradiating it back to Earth.
Effects of volcanism
Volcanism affects the atmosphere in two distinct ways: short-term cooling due to reflected insolation, and long-term warming due to increased CO2 levels. Most of the water vapor and CO2 is collected in clouds within a few weeks to months because both are already present in large quantities, so the effects are limited (Bodenmann et al. 2011). SO2, along with other aerosols and particulates, is responsible for global cooling, nullifying the effects of the greenhouse gas emissions due to its ability to be found higher in the atmosphere and its efficiency at bonding with any water vapor found in the upper “dry” atmosphere. Sulfuric acid is exceptional at blocking solar radiation and it usually takes months to years for it to acquire enough water vapor to fall back to Earth. This means that an already smaller amount of insolation could have reflected at higher rates for up to 3 years (Granados et al. 2012) This is reflected by ice core data and averaged thermometer readings throughout the world. Places in central Canada and Russia experienced warming events of ~0.1 °C which are credited to the chain of eruptions from 1810–1815 (Dai et al. 1991).
Impact of the eruption
By most calculations, the eruption of Tambora was at least a full order of magnitude larger than that of Mount Pinatubo in 1991 (Graft et al. 1993). It is estimated that the top 1,220 metres (4,000 ft) of the mountain was reduced to rubble and ash, effectively reducing its height[clarification needed] by 33%. Around 100 cubic kilometers of rock was blasted into the air, eclipsing the estimated 10 cubic kilometers by its counterpart in Italy, Vesuvius (Williams 2012). Not only were rocks and ash expelled into the atmosphere, but toxic gases were pumped into the atmosphere as well. Many of the residents who survived the resulting tsunami, eruption, or ash cloud became sick due to all of the sulfur, which caused lung infections (Cole-Dai et al. 2009). Volcanic ash was documented to be over 100 cm deep in areas within 75 km of the eruption, while areas within a 500 km radius saw a 5 cm phoenix cloud ash fall,[clarification needed] and ash could be found as far away as 1300 km (Oppenheimer 2003). With this much volcanic ash on the ground, any crops or viable vegetation sources were smothered at a minimum and burned if they were close to the volcano itself. This created an immediate shortage of food in Indonesia, one that only compounded the regular shortage during the winter season (Cole-Dai et al. 2009). The ejection of these gasses, especially HCl, caused the precipitation that followed in the region to be extremely alkaline, killing much of the crops that either survived or were rebudding during the spring. The food shortage was compounded by the Napoleonic wars, floods, and cholera (Oppenheimer 2003).
The presence of ash in the atmosphere for several months after the eruption reflected significant amounts of solar radiation, causing unseasonably cool summers which further drove populations to a food shortage (Oppenheimer 2003). China, Europe, and North America all had well-documented cases of abnormal temperatures, decimating their harvests. These climatic shifts also altered the monsoon season in China and India, forcing thousands of Chinese to flee coastal areas due to regional flooding of the Yangtze Valley (Granados et al. 2012). The gases also reflected some of the already decreased incoming solar radiation, causing a notable decrease in global temperatures throughout the decade, between 0.4-0.7 °C globally. It was so dramatic that that an ice dam was formed in Switzerland during the summer of 1816 and 1817, earning 1816 the title “Year without a summer” or YWAS (Bodenmann et al. 2011). The winter months of 1816 were not very different from years previous, but the spring and summer maintained the cool to freezing temperatures. However, the winter of 1817 radically differed, reaching temperatures below -30 °F in New York, which were cold enough to freeze lakes and rivers used for transporting supplies. Both Europe and North America suffered late freezes that lasted well into June with snow accumulating up to 32 cm in August, which killed recently planted crops, crippling the food industry. Unseasonably cool temperatures reduced the output of crops worldwide: the growing seasons in Massachusetts and New Hampshire were less than 80 days in 1816, citing freezing temperatures as the reason for harvest failure (Oppenheimer 2003). These were visually connected to unique sunsets observed in western Europe and red fog found on the Eastern Seaboard of the US. These unique atmospheric conditions persisted for the better part of 2.5 years (Robock 2000).
Ice cores have been used to monitor atmospheric gases during the cold decade (1810-1819) and the results are puzzling. The SO4 concentration found in both Siple Station, Antarctica and Central Greenland bounced from 5.0[clarification needed] in January of 1816 to 1.1[clarification needed] in August of 1818 (Dai et al. 1991). This means that 25-30 Tg of sulfur was ejected into the atmosphere, most of which would come from Tambora, and was equalized back by natural processes on Earth rather quickly. Another unique factor is that Tambora represents the largest shift in sulfur concentration in the ice cores for the past 5000 years, potentially becoming the single most disruptive event in recorded history. Estimates of the sulfur yield vary from 10 Tg (Black et al. 2012) to 120 Tg (Stothers 2000). The difference between the models are drastic, but many estimates will either average in or agree on a number between 25-30 Tg. The high concentration might explain the stratospheric warming of ~15 °C, resulting in surface cooling that would be a delayed reaction lasting for the next nine years. It is estimated that the stratospheric warming event only lasted four years, but cooler temperatures were documented until 1825 (Cole-Dai et al. 2009). The data presented did not state whether it was a statistically significant difference or just temperatures cooler than “normal.” This has been dubbed a “volcanic winter”, similar to a nuclear winter, due to the overall decrease and abysmal farming conditions (Oppenheimer 2003).
Climate data have shown that the variance between daily lows and highs may have played a role in the lower average temperature because the fluctuations were much more subdued. Generally, the mornings were warmer due to nightly cloud cover and the evenings were cooler because the clouds had dissipated. There were documented fluctuations of cloud cover for various locations that suggested it was a nightly occurrence and the sun killed them off, much like a fog (Oppenheimer 2003). The class boundaries between 1810-1830 without volcanically perturbed years was ~7.9 °C. This is contrasted by the volcanically perturbed years (1815-1817) where the delta was only ~2.3 °C. This meant that the mean annual cycle in 1816 was more linear than bell shaped and 1817 endured cooling across the board. Southeastern England, northern France, and the Netherlands experienced the greatest amount of cooling in Europe; complemented by New York, New Hampshire, Delaware, and Rhode Island in North America (Bodenmann et al. 2011).
The documented rainfall was as much as 80% more than the calculated normal with regards to 1816, unusually high amounts of snow were found in Switzerland, France, Germany, and Poland. This is again contrasted by the unusually low precipitations in 1818 which caused droughts throughout most of Europe and Asia (Auchmann et al. 2012). Russia had already experienced unseasonably warm and dry summers since 1815 and this continued for the next three years. There are also documented reductions in ocean temperature near the Baltic Sea, North Sea, and Mediterranean. This seems to have been an indicator of shifted oceanic circulation patterns and possibly changed wind direction and speed (Meronen et al. 2012). This is further supported by the recorded observations of a British fleet sent to explore the Arctic Circle; they found large ice sheets that were miles off the coast of Greenland, where two years prior they had been shoved along the eastern border of the island. Contemporary scientists attributed the Year Without a Summer to the drifting polar ice sheets rather than the eruption of Tambora because of its proximity to England (Oppenheimer 2003).
Taking into account the Dalton Minimum, and the presence of famine and droughts predating the eruption, the Tambora volcanic event accelerated or exacerbated the extreme climate conditions of 1815. While other eruptions and other climatological events would have led to a global cooling of about 0.2 °C, Tambora increased that number substantially (Dai et al. 1991). This is a case of extreme climate, not extreme weather. Several climate forcings coincided and interacted in a way not experienced since, even with large eruptions since early 20th century. Our current understanding of these events and their link to the Tambora event is well-defined; yet there are many concerns that our understanding of such an event is limited and would not prove substantial if a subsequent eruption of the same magnitude were to occur.