Volcano

Indonesia contains more active volcanoes than any country on Earth. Of the 130 active volcanoes in Indonesia, Merapi is the most active, and has had at least twelve eruptions that killed people. The name Merapi means "Mountain of Fire". The volcano is considered sacred and every year a priest climbs to the top to make an offering.

Here is a graph that shows how many eruptions of Merapi are known during the last 500 years.

What can you say about the number of reported eruptions over the last five centuries?
There were about 16 eruptions during the first 300 years, and about 50 in the last 200 years. The total number of reported eruptions is about 66. This averages out to about one eruption every eight years. During this century, there has been about one eruption every three years.

Merapi is a stratovolcano in central Java. Merapi has had 68 historic eruptions since 1548. The current eruption began in 1987. Because of Merapi's violent past and its close proximity to Yogyakarta it was designated a “decade volcano” and is the target of increased research efforts.

Merapi is a stratovolcano with an active summit lava dome. It is located ~30 km immediately north of Yogyakarta, a city with a population of 500,000. Merapi has the unfortunate distinction of producing more nuee ardentes than any other volcano on Earth. The nuee ardentes result from collapse of the lava dome at the summit. Of the 67 historic eruptions 32 have had nuee ardentes associated with them. Eleven of these eruptions resulted in fatalities. Merapi is closely monitored by the Volcanological Survey of Indonesia. Shortly before this photograph was taken Merapi was generating up to 40 nuee ardentes per day.

In late November of 1994, collapse of a lava dome at Merapi generated pyroclastic flows and surges that traveled as far as 5 miles (7.5 km) from the summit. The flows and surges killed 43 people. The plume associated with the dome collapse rose 6 miles (10 km) above the volcano. Over 6,000 people were evacuated. The eruption also started fires.

The island of Java has more than 600 people per square km, one of the highest population densities in the world. Yogyakarta city, with a population of 3 million, is 15 miles (25 km) south of Merapi. About 70,000 people live in the immediate vicinity of the volcano. Merapi is a basaltic to basaltic-andesite stratovolcano with a summit crater containing an unstable lava dome. Merapi is Indonesia's most active volcano and well known for partial collapse of lava domes and the generation of pyroclastic flows. Pyroclastic flows can travel as far as 8 miles (13 km) from the summit and reach speeds of 70 mph (110 km/hr). Pyroclastic flow deposits can be remobilized as lahars. Direct observations of Merapi have been recorded since 1888. Recent study of tephra deposits on the flanks of the volcano found 27 marker beds that reveal Merapi's past history. The volcano has had numerous moderate to large (1 million cubic m) eruptions. These eruptions typically begin with pyroclastic flows and are followed by widespread pyroclastic air fall. Plinian to subplinian eruptions are common. These older deposits indicate that Merapi is capable of eruption styles very different from those currently observed.

2006, 2001-02, 1992-98, 1972-90, 1971, 1967-69, 1961, 1953-58, 1948-49, 1944-45, 1942-43, 1939-40, 1933-35, 1930-31, 1924, 1923, 1922, 1920-21, 1918, 1915, 1909-13, 1908, 1906-07, 1905, 1902-04, 1902, 1897, 1894, 1893, 1891, 1889, 1888, ?1885, 1883-84, 1878-79, 1872-73, 1872, 1869, 1865-67, 1862-64, ?1854, 1849, ?1848, 1846-47, 1846, 1840, 1837-38, 1832-35, 1828, 1822-23, 1820-22, 1812-13, 1810, 1807, 1797, 1786, 1755, 1752, 1745, 1678, 1677, 1672, 1663, 1658, 1587, 1584, 1560, 1554, 1548, 7630 BC

1992-2002
One of the worst spans of activity of Merapi lasted 10 years. In 1992 Merapi saw an eruption begin that would start the long lasting volcano activity. During this time (1992) a lava dome was extruded, growing by up to half a meter per day. In 94, the dome reached the edge of the crater, ad from then on rock fall from the dome produced frequent pyroclastic flows. In late 94, almost the entire dome collapsed, generating very large pyroclastic flows, which traveled several kilometers from summit and killed 43 people.
Following the large eruption in Nov. of 94, a new dome formed in the crater, and small explosive eruptions continued for several years, generating scores of lava avalanches and pyroclastic flows everyday. Eruptions lasted until late 2002.

The Merapi, 2,968 meters high and situated near the city of Yogyakarta, has already claimed 70 lives in an eruption in 1994 and 1,300 in 1930. It is held to be one of Indonesia's most dangerous volcanoes.

The latest report of activity of Merapi is on March 20, 2007. Based on pilot reports, the Darwin VAAC reported that an eruption plume from Merapi reached an altitude of 6.1 km (20,000 ft) a.s.l. and drifted NE on 19 March.

What might be the cause for the recent increase in the number of reported eruptions of the last two centuries compared to the earlier three?
There are many more eruptions since 1800 than in the three centuries earlier. Two explanations are possible. First, the volcano may have become much more active in the last two centuries, Volcanoes don't erupt the same amount of time forever.
A second possible explanation is that with the increase in population, education, and scientific awareness and reporting over the last two hundred years, there have been more accurate records of the volcano's activity. Which do you think is the best explanation? How could you test which one is best?