Number of deaths caused by the second deadliest earthquake from 1900 to 2010:

230,000
On January 12th, 2010, an earthquake registering 7.0 magnitude on the Richter scale shook Port Au Prince, the densely-populated capital city of Haiti. The American Red Cross initially projected a high-end estimate of 50,000 deaths, but by early February, official estimates of the number of dead rose to 230,000.
Source: Washington Post, 2/10/2010

 
   
  Number of deaths caused by the deadliest earthquake from 1900 to 2010:

255,000
On July 28, 1976, two tremors registering a 7.8 on the Richter scale struck northeast China in a span of 16 hours. Initial reports estimated 700,000 dead but the Chinese government revised the estimates to 255,000 in the following decades.
Source: Wall Street Journal, 1/17/2010

 
   
  Highest death toll ever from an earthquake:

830,000
On Jan. 23, 1556, an 8.0 magnitude earthquake struck Shaanxi province in China, resulting in massive landslides devastating a 500 square-mile area, killing an estimated 830,000 people.
Source: Time.com, 1/13/2010

 
   
 
U.S. Geological Survey
Estimated number of people killed in the Nov. 1985 eruption of Nevado del Ruiz in Columbia:

23,000
On November 13, 1985, a 17,453 foot volcano called Nevado del Ruiz erupted in the Andean Mountains of Columbia. Though it was a relatively small eruption, it resulted in an emormous mud slide which rushed down the valley, destroying the town of Amero some 30 miles away. An estimated 23,000 people were killed in the eruption's aftermath.
Source: Smithsonian, 7/1/1996