( CNN ) -- An Alaska volcano exhibiting `` elevated seismic activity '' has spewed ash clouds skyward -- as high as 20,000 feet above sea level -- an observatory reported Wednesday . As was the case a day earlier , the Pavlof Volcano was on `` watch '' status on Wednesday because of heightened activity , and it was also under an orange code that relates to how its rumblings might affect planes flying over its summit . Both these alert levels are the second most serious out of four options , according to the Alaska Volcano Observatory . The same alert levels also continue to apply Wednesday to the Cleveland Volcano , which like Pavlof is in the Aleutian Island range southwest of mainland Alaska . Lava was reported flowing Tuesday at Pavlof and Cleveland . `` They are very similar , and both have the ability to erupt , '' John Power , a scientist from the U.S. Geological Survey , said this week . Pavlof is the higher of the two volcanoes , reaching to 8,261 feet , and the one that is connected to the Alaskan mainland . The Alaska Volcano Observatory 's Wednesday update noted persisting `` elevated seismic activity '' as well as reports of steam and ash clouds . Web camera images show the plume `` rising occasionally up to about 20,000 feet above sea level , '' the same height at which a pilot on Wednesday reported a `` dark ash cloud '' stretching east-northeast . The volcano observatory also reported a `` diffuse ash plume '' on Tuesday night at an altitude of 15,000 feet and visible downwind for up to 100 miles . Five climbers killed in Philippines after deadly volcanic ash blast . Surface temperatures at the 5,676-foot high Cleveland Volcano remained elevated over the past 24 hours , the observatory said , though there were no explosions detected by infrasound data in that time . The volcano observatory continues to warn that `` sudden explosions of blocks and ash are possible with little or no warning . '' The observatory said Cleveland could also produce ash clouds rising more than 20,000 feet above sea level . Beyond any impact on fish , wildlife and humans , large ash clouds could negatively impact air travel . The National Weather Service has issued a SIGMET , short for significant meteorological information , in areas around the volcanoes . After `` eruptive activity '' last year at the Cleveland Volcano , University of Alaska Fairbanks scientist Steve McNutt said 90 % of air freight from Asia to Europe and North America flies over Alaska airspace , and hundreds of flights fly through Anchorage 's air space daily . `` We think of the Aleutian Islands as being remote and desolate '' Power said , `` but when you come up to 30,000 feet we are talking about 20 to 30,000 people there every single day . '' Power described Pavlof as `` one of the most historically active volcanoes in the Northern Hemisphere . '' Cleveland is also `` very active , '' having last had a large eruption in 2001 . Imposing central Mexican volcano spews ash skyward . CNN 's Amanda Watts contributed to this report .
NEW : National Weather Service issues an advisory for areas around the coast . An expert reports ash plumes 20,000 feet above sea level over the Pavlof Volcano . That and another Alaska volcano are on second highest alert ##s . An expert notes volcanic eruptions over Alaska can seriously affect air travel .