Volcanic Activity
Examination of deposits have dated the two most recent eruptions to around 37,000 and 41,000 years ago. The area exhibits small localised earthquake swarms, bradyseism, and release of carbon dioxide and hydrogen sulphide into the atmosphere. The uplift and earthquake swarms have been interpreted as caused by a slowly growing spherical magma chamber 5-6 kilometres below the surface; some think that it may erupt again; if so, there is risk to Rome, which is only 25 to 30 km away.
There is documentary evidence of an eruption in 114 BC, but the absence of holocene geological deposits has largely discredited it as a volcanic event and instead the account is considered to be a description of a forest fire.
The volcano emits large amounts of carbon dioxide. This can potentially reach lethal concentrations if it accumulates in depressions in the ground in the absence of wind. The asphyxiation of 29 cows in September 1999 prompted a detailed survey, which found that concentration of the gas at 1.5 m above the ground in a residential area on the northwestern flank sometimes exceeded the occupational health threshold of 0.5%. Eight sheep were killed in a similar incident in October 2001.
Read more about this topic: Alban Hills
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