On this day in 1883, the most powerful volcanic eruption in recorded history occurs on Krakatoa, a small, uninhabited volcanic island located west of Sumatra in Indonesia. Heard 3,000 miles away, the explosions threw five cubic miles of earth 50 miles into the air, created 120-foot tsunamis and killed 36,000 people.
Krakatoa lies along the convergence of the Indian-Australian and Eurasian tectonic plates, a zone of high volcanic and seismic activity. Sometime within the past million years, the volcano built a cone-shaped mountain composed of flows of volcanic rock alternating with layers of cinder and ash. From its base, 1,000 feet below sea level, the cone projected about 6,000 feet above the sea.
The only confirmed eruption prior to 1883 was a moderate one in 1680. On May 20, 1883, one of the cones again became active; ash-laden clouds reached a height of 6 miles, and explosions were heard in Batavia (Jakarta), 100 miles away, but by the end of May the activity had died down; it resumed on June 19 and became paroxysmal by August 26.
At 1:00 PM of that day the first of a series of increasingly violent explosions occurred, and at 2:00 PM a black cloud of ash rose 17 miles above Krakatoa. The climax was reached at 10:00 AM on August 27, with tremendous explosions that were heard in Australia and propelled ash to a height of 50 miles. Pressure waves in the atmosphere were recorded around the Earth. Explosions diminished throughout the day, and by the morning of August 28, the volcano was quiet. Small eruptions continued in the following months and in February 1884.
The epic blast destroyed the northern two-thirds of the island; as it plunged into the Sunda Strait, between the Java Sea and Indian Ocean, the gushing mountain generated a series of pyroclastic flows and monstrous tsunamis that swept over nearby coastlines. Fine dust from the explosion drifted around the earth, causing spectacular sunsets and forming an atmospheric veil that lowered temperatures worldwide by several degrees.
With an estimated Volcanic Explosivity Index of 6, the eruption was equivalent to 200 megatons of TNT, about 13,000 times the nuclear yield of the Little Boy bomb that devastated Hiroshima, Japan, during World War 2, and four times the yield of Tsar Bomba , the most powerful nuclear device ever detonated. 165 villages and towns were destroyed near Krakatoa, and 132 were seriously damaged. In addition to the estimated 36,417 people who perished, many more thousands were injured, mostly from the tsunamis that followed the explosion.
The eruption destroyed two-thirds of the island of Krakatoa, yet subsequent eruptions in the area since 1927 have built a new, 1.2 mile-radius island at the same location, rising 1,000 feet above sea level; she is named Anak Krakatau, Indonesian for “Child of Krakatoa.” Periodic eruptions have continued since, with activity in 2009, 2010, 2011, and 2012.
On a related note for North America, Washington’s Mount St. Helens sits in the Cascadia Subduction Zone, a fault line deep in the belly of the planet under the Pacific Ocean. It’s gargantuan size and potential power amaze earthquake experts, who say it likely caused the worst natural disaster in the history of the Pacific Basin back in the 18th century and could do so again. If the Cascadia were to experience a large-magnitude earthquake and rupture, the temblor and resulting 100-foot tsunami could kill more than 13,000 people, injure more than 26,000, and displace or disrupt nearly 3 million, according to one FEMA model.