The questions below are ones that we frequently receive from people interested in Alaska's volcanoes. Since some of these questions are
answered by information in this website (and other websites), we've provided links for you to follow to learn of the answer(s).
Most reports of eruptive activity date from 1760 on although a few vague reports of eruptions exist between 1700 and 1760 (Grewingk, 1850). At least 265 historical eruptions have occurred at 29 Alaskan volcanoes and another 45 are possible since 1760 giving a frequency rate of 1.1 - 1.3 eruptions per year. Since many eruptions early in this period surely went unreported, this is a minimum figure.
The problem of estimating eruption frequency through an analysis of the historical record is well-illustrated in Fig. 5 where the number of eruptions per decade in the Aleutian Arc is plotted for the past 200 years. Reported eruptions show a general increase beginning in the 1870-1880 decade and continuing to the 1920-30 decade where the rate of increase levels off. This increase is assumed to represent expanded travel to this remote area and advances in rapid communication (i.e., newspapers and more recently radio) of eruptive events; interestingly enough, the decades including World Wars I and II show significant decreases. The sharp increase in the 1980-1990 decade has been followed by a return (estimated in part - see caption of Fig. 5) to pre-1980 levels.
A more meaningful eruption frequency estimate can perhaps be calculated over the 50 year period 1945 (the end of World War II) through 1994, a time that marked the beginning of widespread air travel and other commerce in this remote part of the world. During this 50 year interval, 90 eruptions have been reported from 23 volcanoes for a frequency of about 2 (1.8) eruptions per year.
Although these are estimates of the number of separate eruptions per year, many individual eruptive episodes are spread over weeks and even months. In any one year, therefore, it is not unusual for 3 or 4 Alaskan volcanoes to have experienced eruptive activity.
The number of separate eruptions from individual historically active
centers ranges from 1 to 39 and over 60% of the 265 eruptions have come from only 7 volcanoes (Veniaminof, Pavlof, Shishaldin, Akutan, Makushin, Okmok, and Bogoslof Island). These frequently active volcanoes occur along (or, in the case of Bogoslof, behind) a 640 km of the arc in an area where movement between the North American and Pacific plates is most nearly orthogonal. Most of these volcanoes are also marked by long-lived but sporadic strombolian and vulcanian eruptive activity resulting in some difficulty in defining individual eruptions."
From The Catalog of Historically Active Volcanoes of Alaska (1998)