Volcanic activity at the surface can affect the conditions of life. The earth’s crust has a big long continuous crack in it; it’s an undersea crack, and most of the volcanic activity on earth occurs here. Volcanic activity leaks out from this fracture, forming a ridge; this is an underwater mountain range, and in comparison, it dwarfs terrestrial mountains. This continuous ridge is in the ocean basins; it’s often found in middle of a basin, but it can be near a continent. It is 60,000 km long, 1000 km broad and is over 2000 m tall. Here the basalt ocean crust is created from rising magma plumes and volcanic activity spreading outward. Associated with the ridge is tectonic plate divergence, which creates a rift zone (valley) in the midline. The seafloor spreads laterally outward, and becomes covered with increasingly thicker sediments. The basalt ocean crust is heavier than a continent’s granite crust; both “float” on the earth’s hot plastic outer mantle. If the ocean crust and continent crust collide, subduction occurs; i.e., the heavier basalt seafloor crust slides under the floating continental crust and rejoins (melts into) the hot plastic mantle below. In these subduction areas, continental volcanoes release water, carbon dioxide, sulfur (including H2S and SO2) and nitrogen. In other areas, rising mantle plumes can also cause volcanic activity in the earth’s crust above isolated “hot spots.”
In Iceland, the Mid-Atlantic Rift is visible at the surface. The environmental impacts of a very small flood basalt eruption (565 km2 -size of Long Island, NY) in 1783 are notable; this is our only modern-time flood basalt reference. Ben Franklin (American Ambassador in Paris) described 1784 as “a year without a summer.” Ash from the eruption blacked out the sky and crops failed across Europe. In a relatively brief period of volcanic activity, toxins emitted by the fissure eruption damaged and destroyed vegetation from the Arctic Ocean to the Mediterranean.
Air pollution (ash and SO2) was so intense that human health was affected and the national death rate increased dramatically in both England and Fire Down Below 51Retrospective 51
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France. The previously-discussed flood basalt flows associated with the Permian and Cretaceous extinctions were far, far larger than this.
Antarctic ice cores reveal that volcanic activity has tripled in the last 2000 years. Much of the earth’s subduction-related volcanic activity on land borders the Pacific Ocean, in a “ring of fire.” Tambora was the largest volcanic eruption in historic time. Tambora (Indonesia) erupted in 1815 (150km3 of ash) and resulted in another “year without a summer.” Aerosols from the Tambora eruption blocked out sunlight and reduced global temperatures by 3 degrees C (6°F). It snowed during every month of summer in both Europe and America. Famine (e.g. India) was widespread because of crop failures. Krakatoa, a comparatively mild to moderate eruption (25km3 of ash) in 1883, dropped global temperatures 1 degree F for 5 years, temporarily matching the magnitude of the following century’s (20th century) global warming rise of ½ degree C (1°F). The “Little Ice Age” (1200–1900AD) cold was associated with a very high frequency of Krakatoa-level volcanic eruptions. Even recently, Pinatabo erupted in the Philippines in 1991 (25km3); temperatures again dropped ½ degree C (1°F), temporarily masking global warming at that time.
A single volcano can cause even greater changes in the conditions of life. A notable world climate change occurred around 75,000 years ago, when “super volcano” Mt. Toba in Sumatra (Indonesia) erupted. At that time, 800 cubic kilometers of ash (Mt. St. Helens had 1.2km3) caused a
“volcanic winter” that lasted 6 years. The volcanic winter was followed by, for mankind, 1000 years of the coldest time in the present ice age on record (during Wisconsin ice period). Over 90% of sunlight was blocked;
plant growth stopped. Temperatures dropped as much as 15 degrees C (30°F). Rainfall ceased. From an estimated near-million humans on earth, genetic studies suggest that less than 10,000 of our ancestors survived.
The survivors (with the greatest genetic diversity today) were located in equatorial East or Southeast Africa. Ocean currents (Easterly Equatorial Countercurrent) and upwelling atmospheric conditions along the equator dispersed the ash cloud to higher latitudes. While 15 cm of ash fell on southern India, equatorial Africa’s more remote location would have received far less. Later on, as temperatures fell sharply, the equatorial proximity contributed to moderating the severe cold environmental conditions. Even though the glaciers never approached the equator, ice age cold and drought challenged our survival. Lake Malawi (East Africa-550km long and 700m deep), the third largest lake in Africa and ninth largest on earth, was reduced to a couple of pools no more than 10 km across and 200m deep. Only a prolonged continent-wide drought could have had this effect. “Survival of the fittest” produced a new kind of man for the upcoming great leap forward (What doesn’t kill you…). Did this near-extinction of mankind play a role in making Homo sapiens even wiser?
Modern man left Africa once again, heading north and east. Neanderthals and the hobbit-like Homo erectus also survived. The near-extinction of man was undoubtedly accompanied by other notable extinctions. Climate dominates the environment.
Yellowstone is another “super volcano.” Yellowstone erupted 630,000 years ago, 1.3mya and 2.1mya; is it about due for another eruption? Nearly 400 cubic kilometers of debris were liberated at the last eruption (½ the size of the Mt. Toba eruption). A similar eruption today would immediately kill all complex life within 100km. Thousands of people would die as the superheated cloud of dust, sulfuric, nitric and hydrochloric acid sweeps across Middle America. The volcanic dust would spread across all of America, burying the Midwest. Inhaling the dust with broken-glass sharpness, Marie’s disease killed extensive numbers of prehistoric life in far less extensive past volcanic eruptions. Silicosis-induced lung cancer would continue far into the future. Billions of people would die in the volcanic winter and famine that would last several years. The U.S. would not recover anytime soon. The entire world would not recover anytime soon. While it will not cause a mass extinction, or even a lesser extinction event, it could still cause a notable (small) extinction event. Like an ice age Milankovitch Cycle, a loss of numerous species, even genera, could be expected. In order to erupt, Yellowstone’s magma chamber needs to be 50% filled with molten rock; its now estimated at 10–30%.
Some of the greatest volcanism the world has seen in the past half-billion years occurred at the end of the Permian and Cretaceous periods;
the floods of basalt lava respectively covered Siberia (2M km2) in an area equal to the size of the United States, and covered most of India (1.5M km2). Curiously, neither of these massive flood basalt flow areas is located in an ocean basin ridge spreading area. It is possible that the end-Permian impact in Antarctica is associated with the volcanic activity of the Siberian traps? Could the Antarctic impact crack the crust at the opposite pole of the earth and cause Siberia to be covered with lava at the end of the Permian? The end-Cretaceous basalt flows that covered India (Deccan traps) occurred (65.5mya), following the Manson, Iowa impact of 74mya, on the opposite side of the earth. Rocks from the time of the Manson impact show intense volcanic activity. This impact and basalt flood happened before the Yucatan impact of 65mya; did the former impact promote this unusual basalt flood? In both cases, the earth actually split apart and covered entire continental areas with massive flows of lava. Flood basalt eruptions that cover such large areas of the planet are exceedingly rare.
Could it be shock wave convergence on the opposite side of the earth? To some, this may seem like a stretch, but is no more far-fetched than the chances of increased occurrences of earthquakes or volcanic eruptions in areas directly under, and following, a solar eclipse, which does seem to Fire Down Below 53
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happen. Jupiter’s moon’s Io and Europa demonstrate possible exaggerated examples. Io demonstrates massive volcanic eruptions as it is turning it inside out at a rate of 1cm every 3000 years. Europa’s gravitational flux causes extensive fracturing of the 25 km of surface ice as the massive watery tides rise to this surface. The solar system demonstrates even more evidence of shock-wave crust fracture in the following examples. Jupiter’s moon, Callisto is covered with impact craters; Valhalla Crater is surrounded by concentric ripples that extend over 1/3rd of the way around that moon; similar ripple patterns are seen around all of Callisto’s numerous large impact craters. Saturn’s moon, Mimas, is scarred by an impact crater that covers nearly 1/4th of its surface; stress marks on the opposite side indicate that the impact nearly destroyed it. Saturn’s moon, Tethys, is girdled by Ithasca Chiasmata, a huge crack on the opposite side of impact crater Odysseus that covers over 2/3rds of the circumference.
Uranus’ moon, Titania, is completely covered with impact craters and a web of interconnected valleys (chiasmata). Both Siberia and India were near the exact opposite side of the earth at the time of each impact (highly uncommon coincidence?). Could there have been more than one impact, in the area of eruption itself? While dual opposite strikes are possible in both instances, this degree of coincidence would seem to be even more unlikely. There does seem to be a strong association between extra-terrestrial impacts and volcanism. Recall the impact in Canada, 214 million years ago; the impactor was a 5 km meteor; the crater diameter is 100 km.
It is believed to be one of several responsible for initiating a mass extinction found at the Triassic-Jurassic boundary layer. Following this, a massive rift (that approximates the mid-Atlantic rift today) poured forth another massive basalt flow around 200mya (similar in size to the Siberian traps);
the supercontinent of Pangea split apart and the Atlantic Ocean began to form. Additionally, high levels of volcanism are associated with impacts of 55mya and 34mya, and their respective Paleocene and Eocene extinctions (Levinton—chapter on Patterns of Diversity, Origination and Extinction). There are also data that imply comet/meteorite impacts correlate with Yellowstone eruptions 1.3 and 2.1 million years ago. The impact that caused the Yellowstone “hot spot” probably occurred about 17.5mya (Burchard).