text: A volcano in Chile that has laid dormant for more than 40 years has suddenly erupted, causing a thick plume of ash to cloud the sky while thousands of people living in its shadow were forced to flee. Volcano Calbuco, in the country's south, is believed to be among the three most dangerous of Chile's 90 active volcanoes, but was not under any special observation before it suddenly sprung into life at around 6pm local time. An estimated 1,500 people were forced to flee the nearby town of Ensenada after the eruption, while several smaller townships were also cleared. Scroll down for video . Up in smoke: Volcano Calbuco, in southern Chile, has erupted forcing 1,500 residents from Ensenada, about 10 miles away,  to flee their homes (pictured, a view of the eruption from Puerto Montt, a small city around 20 miles from the volcano) Boom: The eruption sent a huge plume of gas and ash soaring into the atmosphere which was visible from up to 100 miles away (pictured, the scene in Puerto Varas, around 25 miles away) Unexpected: The volcano last erupted in 1972, and while it is widely believed to be among Chile's most dangerous, it was not under observation before it erupted today (the eruption pictured from Puerto Varas) Active: Volcano Calbunco is regarded as being among Chile's three most dangerous volcanoes, and is part of an active chain of around 500 that cover the south of the country . Panic: Residents from Ensenada described 'apocalypse scenes' after the volcano erupted about 6pm local time, with local authorities setting up a 12.5-mile exclusion zone around it . Smoke and lava can be seen spewing from the Calbuco volcano in this picture taken from the shores of Lake Llanquihue in Puerto Varas . An electrical storm lights up the night sky as a huge column of ash and lava shoots out of the volcano. The eruption sparked a red alert in the port city of Puerto Montt . The volcano is located near the tourist town of Puerto Varas and the city of Puerto Montt, a little more than 620 miles south of Chile's capital, Santiago. The National Mining and Geology Service issued a high alert, setting up an exclusion zone of 12.5miles around the volcano, barring access to the area. Trevor Moffat, who lives in Ensenada, some six miles from the volcano, said the eruption happened without warning. Volcano Calbuco's last major eruption happened in 1961, with a weak eruption following in 1972. The Calbuco volcano in southern Chile erupted for the first time in more than five decades on Wednesday, sending a thick plume of ash and smoke several kilometres into the sky . Explosion: Residents in nearby Puerto Varas go about their business while in the background the ash cloud from Volcano Calbuco is seen . Destructive: Volcanoes occur at the edges of tectonic plates which make up the earth's crust, either where these plates are moving toward or away from one another. Eruptions occur when magma  forces its way to the surface, exploding through weak points in the crust . Plume: While most people think of volcanoes as spewing lava, many eruptions take the form of super-heated gas and ash which is pushed through the earth's crust, covering the sky . Not another one: Southern Chile is a sparsely populated region of high volcanic activity. In March, volcano Villarrica, about 155 miles to the North, also erupted in spectacular fashion, sending a plume of ash and lava high into the sky . He said: 'It sounded like a big tractor trailer passing by the road, rattling and shaking, guttural rumbling ... we left everything there, grabbed my kid, my dog, got in the car with my wife. Mr Moffat, who was originally born in Canada, said he was now driving his family to Puerto Varas. He added: 'All the neighbors were outside, a lot of young people crying. Armageddon type reaction.' Television pictures showed a spectacular mushroom-shaped column billowing into the sky with occasional lighting bolts shooting through it. The eruption was seen up to 100 miles away in neighbouring Argentina. Danger: Residents from nearby towns said people were crying in the streets after the volcano erupted without warning at 6pm local time . Shocking: While the first eruption occurred in the middle of the afternoon, the plume of ash and smoke was visible well into the evening from towns 100 miles away in Argentina . Blanket: The last major eruption here was in 1961 when lava flows filled the top crater before spilling down the sides and into a nearby lake. There was another minor eruption in 1972 . Distant: A view of the ash cloud from the Nahuel Huapi lake, around 100 miles away from the volcano in neighbouring Argentina . Derek Way, a resident of Puerto Varas,, said: 'There are a lot of people out in the streets, many heading to the gas stations to fill up on gas. A friend told me to fill everything we have with water.' Chile, on the Pacific 'Rim of Fire', has the second largest chain of volcanoes in the world after Indonesia, including around 500 that are potentially active. In March, volcano Villarrica, also in southern Chile, erupted in spectacular fashion, sending a plume of ash and lava high into the sky, but quickly subsided. Volcanoes occur at the edges of tectonic plates which make up the earth's crust, either where these plates are moving toward or away from one another. Eruptions occur when magma from the Earth's core forces its way to the surface, exploding through weak points in the crust.
target: Volcano erupted without warning at around 6pm local time with 1,500 people forced to leave their homes .
  Residents described people crying in the streets as they fled in the aftermath of the 'apocalypse-like' eruption .
  It is the first time the volcano has been active since 1972, and the first major eruption there since 1961 .
  The plume of ash and smoke blanketed the sky and was visible in towns up to 100 miles away in Argentina .