The Spire of Pelée
In 1902, Mount Pelée on the island of Martinique unleashed one of the deadliest volcanic eruptions of the 20th century. After a period of a few weeks activity, on May 8 it exploded, producing a pyroclastic flow nicknamed a nuée ardente, which translates to “glowing cloud”.
Gases dissolved in the magma broke free, tearing apart the molten rock inside the volcano as it escaped.That mixture of gas and rock enveloped the city of St. Pierre below it, leaving only a handful of known survivors out of a city of 28,000.
After the climactic eruption, Mount Pelée calmed down, but later in the year it began a new phase of activity. Rocks that could be seen glowing at night began oozing out of the volcano, pushing upward and forming this spire that eventually reached over 300 meters in height. The spire grew as much as several meters per day until it finally collapsed in early 1903.
This sequence reminds me of more recent events, such as the recent eruptive activity at Mt. St. Helens, and implies a more general set of processes. First, the volcano became active, waking up over a period of days to weeks as magma entered the system. Then, there was a huge explosion, dramatically releasing volatile gases like water and CO2 that were dissolved in the magma. Finally, after the large burst of volatiles was released, sticky, leftover, high-viscosity magma forced its way up the throat of the volcano, building a spire on the site where the explosion took place.
-JBB
Image credit: Lacroix, A., 1904, La Montagne Pelee et ses eruptions: Paris, Masson et Cie, 622 p.
http://www.geology.sdsu.edu/how_volcanoes_work/Pelee.html
http://content.time.com/time/specials/packages/article/0,28804,2014572_2014574_2014625,00.html