ONE of the world's most deadly volcanoes, which killed thousands of people when it erupted three decades ago, is showing signs of another monster eruption. The ice-capped Nevado del Ruiz covers more than 120 miles squared in central Colombia. It has shown significant activity in recent weeks, leading to the issuing of a yellow eruption warning by The Colombian Geological Service. There are fears the volcano could unleash deadly mudslides known as lahars if activity continues. In November 1985 a huge eruption there caused four lahars to unexpectedly speed down the volcano at up to 18.6 miles per hour, killing 23,000 people. It was the worst eruption in South America's recent history and the fourth worst in the world. The town of Armero, 30 miles from the base was left with no warning and little time to prepare or evacuate. Colombian officials were at the time slammed for not heeding warnings from volcano experts about the mud flow risk. There have been several toxic ash cloud emissions