Hiroshi HAYASAKA

In 2004 and 2005, many large-scale forest fires had occurred in Alaska. The burnt area in 2004 was 26,142 km2 and it was 18,816 km2 in 2005. They were respectively the first and the third historical record since 1956. The cause of these fires is now under investigating. This is a preliminary report on these fires. In 2004, severe lightning in June and July had caused most fires. Not a few fires grew into large-scale fires with the help of severe drought and Chinook or foehn phenomena. As a result, the total burnt area reached about 26,000 km2 and it is almost the same area of the Lake Erie. One of the large-scale fires called “Boundary fire ” occurred near Fairbanks was chosen to investigate fire growth process in detail. Boundary fire has been considered as a second largest fire in 2004. Fire growth of large-scale forest fire was clearly showed by some analytical results of the hot spot (fire), climate, and fire history data. “Boundary fire ” and other fires became a large-scale fire for the following processes. 1. Sever lightning occurred in the beginning of June and ignited various places in the boreal forest in Alaska. One of these lightning ignited the forest in “Boundary fire ” area on 13th June and first hot spot was detected on 18th June. 2. First hot spot peak appeared on 30th June due to the dry weather conditions that made by Chinook. 3. Most fires were self-extinguished or lost activeness due to the large massive smoke from severe fires. 4. Second hot spot peak was found on 13th July and made by drought from the beginning of June. 5. Most fires in the second peak were extinguished due to the rainfall of the end of July. 6. Third hot spot peak appeared on 11th August due to the drought from the beginning of August