when Nevado del Ruiz the volcano in Columbia erupted in 1985 I think.. the eruption caused Lahars to flow through the town of Armero.. it caused more than 23,000 deaths, about 5,000 injury's, and more than 5,000 homes were destroyed... Three quarters of the population of Armero were killed by the lahars.
Id say that mount vesuvius (pompeii) is the most rememberable and was pretty devasting but as for the worst......hey i found a list
* Athens, 430 B.C.: Typhus epidemic
* Pompei, 79: Volcanic eruption
* Antioch, Syria, 526: Earthquake (250,000 dead)
* Costantinopole, 542: Bubonic plague
* Beirut, Lebanon, 551: earthquake and tsunami (tens of thousands dead)
* Japan, 1181: famine (100,000 dead)
* Holland, 1228: sea flood (100,000 dead)
* Chihli, China, 1290: Earthquake (100,000 dead)
* Europe and Asia, 1346-52: Bubonic plague or "black death" (one third of the European population dead plus millions in Asia and North Africa for a total of 25 million)
* Shensi, China, 1556: earthquake (800,000 dead)
* Napoli, Italy, 1631: Mt Vesuvius erupts (3,000 dead)
* Havana, 1648: Yellow fever epidemic
* Sevilla, Spain, 1649: Plague (80,000 dead)
* Turkey, 1668: earthquake (8,000 dead)
* Hokkaido, 1730: Earthquake (140,000 dead)
* Lisbon, 1755: earthquake and tsunami (30,000 dead)
* Calcutta, 1737: Earthquake (300,000 dead)
* Bengal, India, 1769: famine (10 million dead)
* India, 1775: Tsunami (60,000 dead)
* Northamerica, 1775-82: Smallpox (130,000 dead)
* Iran, 1780: earthquake (200,000 dead)
* Caribbeans, 1780: Hurricane (22,000 dead)
* Philadelphia, 1793: Yellow fever epidemic (5,000 dead)
* Sumbawa, Indonesia, 1815: Mt Tambora erupts (88,000 dead)
* Japan, 1826: Tsunami (27,000 dead)
* Cairo, 1831: Cholera epidemic, which spreads to London
* London and Paris, 1832: Cholera epidemic (25,000 dead)
* Ireland, 1845: famine (one million dead)
* Mapoli, Italy, 1857: earthquake (11,000 dead)
* India, 1864: Cyclone (70,000 dead)
* France, 1870-71: Smallpox (500,000 dead)
* Bangladesh, 1876: Cyclone (200,000 dead)
* China, 1876-78: Drought (9 million dead)
* China, 1881: Typhoon (300,000 dead)
* Indonesia, 1883: Tsunami (36,000 dead)
* Huayan Kou, China, 1887: Yang-tse Kiang flooding (one million dead)
* Mino-owari, Japan, 1891: earthquake (7,000 dead)
* Sanriku, Japan, 1896: Tsunami (27,000 dead)
* India, 1897: earthquake (1,500 dead)
* Galveston, 1900: Hurricane (8,000 dead)
* Martinique, 1902: Volcano (38,000 dead)
* San Francisco, 1906: earthquake and fire (3,000 dead)
* Colombia, 1906: earthquake (1,000 dead)
* Chile, 1906: earthquake (20,000 dead)
* China, 1907: famine (20 million dead)
* Messina, Italy, 1908: 7.5 earthquake (70,000 dead)
* Mexico City, 1911: earthquake
* Worldwide, 1918: Influenza pandemic (25-100 million dead)
* Gansu, China, 1920: 8.6 earthquake (200,000 dead)
* Ukraine, 1921: Famine (5 million dead)
* Yokohama, Japan, 1923: 8.3 earthquake (143,000 dead)
* Nanshan, China, 1927: 8.3 earthquake (200,000 dead)
* China, 1928: Famine (3 million dead)
* Florida, USA, 1928: Hurricane (1800 dead)
* China, 1931: Flooding (3.7 million dead)
* Ukraine and Russia, 1932: Famine (5 million dead)
* Gansu, China, 1932: 7.6 earthquake (70,000 dead)
* Sanriku, Japan, 1933: 8.4 earthquake (3,000 dead)
* Bihar, India, 1934: 8.1 earthquake (10,700 dead)
* Quetta, Pakistan, 1935: 7.5 earthquake (60,000 dead)
* China, 1936: Famine (5 million dead)
* New York, USA, 1938: Rains (600 dead)
* Erzincan, Turkey, 1939: 7.8 earthquake (33,000 dead)
* China, 1941: Famine (3 million dead)
* Bengal, India, 1943: famine (3.5 million dead)
* Tonankai, Japan, 1944: 8.1 earthquake (1,200 dead)
* Nankaido, Japan, 1946: earthquake (1,330 dead)
* Ashgabat, Turkmenistan, 1948: earthquake (100,000 dead)
* Assam, India, 1950: earthquake (1,526 dead)
* Holland, 1953: Sea flood (1,794 dead)
* Iran, 1953: Rain flood (10,000 dead)
* Louisiana, USA, 1957: Hurricane (400 dead)
* Worldwide, 1957: Influenza pandemic (about four million dead)
* Japan, 1958: Typhoon (5,000 dead)
* China, 1958-61: Famine (38 million dead)
* Morocco, 1960: earthquake (10,000 dead)
* Chile, 1960: 9.5 earthquake (5,700 dead)
* Mt Huascaran, Peru, 1962: Volcano eruption (3,000)
* India, 1965: Famine (1.5 million dead)
* Worldwide, 1968: Influenza pandemic (about 750,000 dead)
* China, 1969: Famine (20 million dead)
* North Peru, 1970: 7.8 earthquake (66,000 dead)
* Bangladesh, 1970: Sea flood (200-500,000 dead)
* Vietnam, 1971: Red River flood (100,000 dead)
* Nicaragua, 1972: earthquake flood (10,000 dead)
* Bangladesh, 1974: floods (28,000 dead)
* Ethiopia, 1974: famine (200,000 dead)
* Haicheng, China, 1975: 7.0 earthquake (10,000 dead)
* Tangshan, China, 1976: 8.0 earthquake (750,000 dead)
* Guatemala, 1976: earthquake (23,000 dead)
* Andhra Pradesh, India, 1977: cyclone (10,000 dead)
* Caribbeans, 1979: Hurricane (2,000 dead)
* Mexico, 1982: volcanic eruption (1,800 dead)
* Yemen, 1982: earthquake (3,000 dead)
* Bhopal, India, 1984: Chemical pollution (3,800 dead)
* Ethiopia, 1984: Famine (900,000 dead)
* Ciudad de Mexico, 1985: 8.1 earthquake (9,500 dead)
* Colombia, 1985: Volcano (25,000 dead)
* Armenia, 1988: earthquake (55,000 dead)
* Colombia, 1985: eruption of Nevado del Ruiz (23,000 dead)
* Bangladesh, 1988: Monsoon flood (1,300 dead)
* Gilan and Zanjan, Iran, 1990: 7.7 earthquake (35,000 dead)
* Bangladesh, 1991: tsunami (138,000 dead)
* Latur, India, 1993: earthquake (22,000 dead)
* Kobe, Japan, 1995: earthquake (5,500 dead)
* Niger, 1995: meningitis epidemic (3,000 dead)
* Chicago, USA, 1995: heatwave (739 dead)
* North Korea, 1995-98: Famine and floods (3.5 million dead)
* West Africa, 1996: meningitis outbreak (25,000 dead)
* Tashkent, Uzbekistan, 1996: earthquake (??,000 dead)
* Papua New Guinea, 1998: Tsunami (2,200 dead)
* Yangtze Kiang, China, 1998: flooding (3,600 dead)
* Central America, 1998: Hurricane Mitch and floods (12,000 dead)
* Afghanistan, 1998: Earthquakes (10,000 dead)
* Colombia, 1999: earthquake (1,185 dead)
* Izmit, Turkey, 1999: earthquake (17,000 dead)
* Taiwan, 1999: 7.6 earthquake (2,400 dead)
* Orissa, India, 1999: Cyclone (7,600 dead)
* Venezuela, 1999: Floods (20,000 dead)
* Gujarat, India, 2001: earthquake (20,000 dead)
* El Salvador, 2001: earthquake (850 dead)
* Afghanistan, 2002: earthquake (2,500 dead)
* Algeria, 2003: earthquake (2,266 dead)
* Asia, 2003: SARS (744 dead, mostly in China)
* Andhra Pradesh, India, 2003: Heat wave (1,300 dead)
* France, Spain and Italy, 2003: Heat wave (50,000 dead)
* Bam, Iran, 2003: earthquake (26,300 dead)
* Al-Hoceima, Morocco, 2004: earthquake (571 dead)
* Haiti and Dominican Republic, 2004: rains (2,400 dead)
Philippines, 2004: typhoon (1,000 dead)
* China, 2004: floods (1,300 dead)
* Southeast Asia, 2004: tsunamis caused by 9.0 earthquake (111,000 dead
* Zarand, Iran, 2005: earthquake (500 dead)
* Nias, Indonesia, 2005: 8.7 earthquake (1000 dead)
*Mumbai, India, 2005: monsoon (1,000 dead)
*China, 2005: floods (567 dead)
*Louisiana and Mississippi, USA, 2005:"Katrina"hurricane (1,417 dead)
* Niger, 2005: famine (10,000? dead)
* Kashmir, 2005: earthquake (80,500 dead
* Central America, 2005: floods (1,400 dead,
* Philippines, 2006: mudslides (1,800)