Yesterday's post considered geologic events which are occurring in Italy, and how the basic principles involved in what is happening in that country may also apply in the Cascadia region. As we begin this discussion, let us consider that very explosive volcano near Rome, which is called Colli Albani. In recent times, this volcano has been slowly bulging, but scientists are currently assuring the world that it will not erupt violently for at least 1,000 years. But, let us consider how quickly things can change, when Nature finally begins to move. This information does have application in Cascadia and elsewhere.
Let us look at just one example of how quick and unexpectedly things can change, geologically. Let us look back to a geologic event which began on February 20, of 1943. On this day, a farmer in Mexico was working in his cornfields. To him, it was just another normal day. He was going about his business and getting the ground ready for planting his new crop. A page, linked here, gives the basic details about what happened next. When the farmer went to one of his fields, he noticed something a bit different. The linked page states: "...On top of a small hill in the field a huge crack, over six feet wide and 150 feet long, had appeared in the earth."
Yes, it appears this large crack was something new -- something which had formed since the last time the farmer had been to this field. Yes, it may have been very strange to have this feature in the ground, but, oh well, it was only about one foot deep. So, let's get back to getting ready for farming. As the farmer worked, suddenly, there was a rumbling sound and the ground started shaking. The ground where the crack was located began to swell and rise. There were strange hissing noises and ash was pouring out of a hole where the crack was. Smoke was coming out of the ground now, and the noises got louder and continuous. About this time, the farmer made his swift escape.
It is important to note that there had been warning signs prior to the rise of this rapidly growing volcano. The page linked above states that local residents of Paricutin "thought they had been hearing the sound of normal thunder in the weeks that preceded the eruption, though they were puzzled by the lack of storm clouds in the sky." So, what what producing all these rumbling or booming sounds? It was caused by "the movement of magma deep inside the earth." The local residents also felt ground tremors, as Nature was preparing to build the volcano of Paricutin.
Paracutin is classed as a scoria cone. Scoria cones are also called "cinder cones."(1) This type of volcano can suddenly "appear out of nowhere" and quickly build into a rather large, steep-sided mountain. At this point, it should be noted that there is a large cinder cone right in the middle of Portland, Oregon. This volcano is called Mount Tabor.(2) Rocky Butte, Powell Butte, and Kelly Butte are also volcanic cinder cones. Let it be further noted that many residences are built on these volcanoes.
Portland is actually built in the Boring Lava Field.(3) There are "at least 32 cinder cones and small shield volcanoes lying within a radius of 13 miles of Kelly Butte," on the east side of Portland. But, as usual, there is more to this story. In the Portland area there are at least 95 lava vents. These vents are even included in the West Hills of Portland. The 95 vents are noted on a map, which is linked here. The bottom line is, there are many residences scattered around and over virtually all of these lava vents.
In former times, scientists did not believe that large earthquakes could trigger volcanic activity. But now, it appears that some of their thinking is beginning to change and some now tend to believe that major earthquakes may possibly trigger volcanoes. One example of this change in thinking is a page containing information about two volcanoes which erupted after the M9.3 Sumatra earthquake of 2004. That page is linked here.
A National Geographic page, which includes information relating to earthquake-induced volcanic eruptions, is linked here. A webpage, linked here, speaks of the Cascade Graben in the Cascade Mountains in Oregon, in which are located a number of volcanoes. This graben is under compression at this time. But, the information notes that "during a large Cascadia subduction earthquake, the normal stress on the graben would reverse..." That means that the stress would then become extensional. This means that there could be a stretching or weakening of the continental crust in this area.
When the continental crust around volcanoes in the Cascade Mountains is stretched or weakened, the page states that "this would enhance the possibility of an eruption where magma accumulation is critically stressing the crust..." Let us consider this concept further. Is there a chance that during the next Cascadia mega-quake, the earth's crust in the Portland area and surrounding region could once again be weakened? Is there a chance that cracks could form in the ground in this region? And finally, is there a remote chance that this region could experience volcanic activity, once again, with lava pouring out of the ground and consuming whatever it comes in contact with?
For further reading:
Current Expectations for a Cascadia Mega-Quake
https://cascadian.neocities.org/cascadiaquake.htm
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