Saturday, January 10, 2009

Yellowstone's Earthquake Activity



I've been following the news about the earthquakes in Yellowstone. Beginning on December 26 there have been a swarm of earthquakes under Yellowstone Lake. There was a lull in activity for a few days, but they have started back up although the center has moved about 10 miles. While most have been very small quakes, the largest have been up to 3.9 on the Richter Scale. While I first saw the news about the quakes on MyYahoo, I keep up to date with Jim MacDonald's Yellowstone Newspaper. He surfs the web and provides links to news stories, articles and blogs related to Yellowstone National Park.

I first visited Yellowstone as a child. My husband and I have been back a number of times over the years, staying longer each visit. We keep the natural trail guides from each trip, because as an active geothermal area the information as to activity changes over time. It is interesting to see which features are active today vs when we first went. During our early visits to the park, no mention was made of the caldera because the Yellowstone caldera is so large that it took satellite imagery for it to be discovered. According to Wikepedia, a caldera is a cauldron like volcanic feature formed by the collapse of land following a volcanic eruption. A caldera forms after a volcano empties its magma chamber and the chamber's ceiling is no longer strong enough to hold the volcanic rock above it. The first caldera I ever saw was the Valles Caldera in New Mexico. (Remember - at the time we did not know Yellowstone was a caldera.) It is 14 miles in diameter and we drove straight across it before it became a National Preserve. It was an impressive site to be on the flat land between the far away ridges of the rim of the caldera.

The discovery about Yellowstone's explosive volcanic past occurred during the 1980's. Since then a lot of study and research has revealed an amazing history of eruptions - both great and small. Yellowstone is classified as a supervolcano. According to Wikepedia, a supervolcano is a volcanic eruption which is substantially larger than any volcano in historic times (generally accepted to be greater than 200 cubic kilometers). This kind of eruption is typically sufficient to cause a long-lasting change to weather (such as the triggering of an ice age) sufficient to threaten the extinction of species, and cover huge areas with lava and ash. I've seen the BBC documentary,Supervolcano . It gives a very scary presentation as to what could occur if Yellowstone had that kind of eruption today.

Because I do pay attention to news about Yellowstone, I know that a few years ago, they had to close part of Norris Geyser basin because the ground had gotten too hot and there were noxious gases present. I also know that the ground has been rising at a more rapid pace than "normal" the last few years. Since 2004, the park has been rising 3 inches a year more than three times faster than ever measured before. So when the news about these earthquakes that were happening at a much higher than normal frequency, I was intrigued and concerned. While I do not really believe that these are precursors to a volcanic event that will cause extinctions, I believe that something very interesting is happening up there right now.

Here are some things I learned as I looked deeper into Yellowstone's volcanic past.

Geologic time is always amazing because it tends to be measured in millions of years and hundreds of thousands if years orather than decades or hundreds of years. Yellowstone's caldera forming eruptions go extremely far back in time:

2,100,000 years ago - Caldera forming eruption that created Huckleberry Ridge
1,300,000 years ago - Caldera forming eruption that created the Island Park Caldera
640,000 years ago - Caldera forming eruption that created the Lava Creek Tuff

Deposits of ash from these eruptions have been found as far away as Iowa, Louisiana, and California.



If Yellowstone were to erupt at one of these levels all of North America and in some ways the entire Northern Hemisphere would have severe effects.

Fortunately, not all of Yellowstone's eruptions have been that catastrophic. About thirty eruptions of rhyolitic lava flows have amost filled the Yellowstone Caldera since the last major caldera forming eruption 640,000 years ago. These flows may move slowly, but are very destructive. The last major lava flow seems to be about 70,000 years ago.

Earthquakes are common - in fact 1,000 to 3,000 earthquakes are typical in a given year. Another source said the usual number of quakes was 2000 per year. However, with over 900 in roughly 2 weeks, it is easy to see that the current activity is more than the norm. Earthquakes can change the patterns of the geyser eruptions - making some more active and others less so. The 1959 Hebgen earthquake was one of the stronger ones at 7.5 on the Richter Scale. Part of the mountain slid into a campground and dammed the Madison River creating Hebgen Lake. 28 people in the campground were killed. A 1975 quake near Norris Geyser Basin registered 6.5 and was felt throughout the area.

The last kind of eruptive activity are hydrothermal explosions.From Hanksville.org: "Hydrothermal explosions occur when ground water, heated above the boiling point (superheated) expands explosively after a rapid decrease in pressure as the water nears the surface. Ten such hydrothermal explosion craters are found in Yellowstone." 13,800 years ago the largest hydrothermal exposion created a 1.5 mile crater at Mary Bay. A 1989 hydrothermal explosion at the Porchop Geyser in Norris Geyser Basin threw rock debris fifteen feet across the spring. Hydrothermal exposions seem to be independent of volcanic magma flow - none were followed by an eruption of magma.

In 2003, a long linear fissure on a hillside above Nymph Lake north of Norris Geyser basin vented steam and threw rocks.

The geysers, mud volcanoes, and hot spring pools are also effects of the magma heat source under Yellowstone.

This chart summarizes the kinds of activity I've been describing.



Right now Yellowstone National Park is buried underneath a thick layer of snow. It is hard for scientist to get to the surface area near where these earthquakes originate. I wonder if there will be evidences of hydrothermal explosions in the spring when everything thaws out. It is going to be interesting to watch the events unfold in Yellowstone. Most likely, these quakes will die down and become just another footnote in the history of Yellowstone. But, it is always possible that they are the precursor of something larger. Will we be the generation of people that get to witness a new lava flow in Yellowstone? I have to say I would rather not be in the generation of people who survive a cataclysmic caldera forming eruption.

Watch for part two where i will compare Yellowstone's caldera forming earthquakes with other earthquakes around the world.

For more reading, here are some of the sites I used to research this blog:
The charts came from the USGS service site.

References:

US Geological Survey
Armageddon Online
Time
Yellowstone National Park - Calderas
Daily Kos

Additional Links:
For most recent earthquake activity at Yellowstone: University of Utah Seismograph Stations
The USGS update as of January 8th also reports 900 earthquakes in Yellowstone between December 26, 2008 and January 8, 2009.
University of Utah's site has a Deseret News article from 1975 listing the 1959 Yellowstone Quake as 7.1. However, the The USGS site reports it as 7.5 and Wikepedia's 1959 Yellowstone Earthquake article lists the magnitude as 7.3-7.5.
My husband found a USGS Animated Earthquake Map for Yellowstone. It shows where last weeks quakes were and where the new ones are in relation. (Granted, the link worked a few minutes ago and isn't working as I post this, hopefully it will work for my readers.)

8 comments:

Dan Owens said...

Very well written. I've been following the earthquake swarm and this is the best summary I have read.

Mary Ann Melton said...

Thanks, Dan!

Anonymous said...

Right for starters you should get your facts right, the quake of 59 was a 7.1 not 7.5,as for there being 900 quakes in 2 weeks no between 5 & 6 hundred.
If you carry on with this sort of reporting you are going to scare people and that will not do your reputation any good.

Mary Ann Melton said...

The Salt Lake Tribune report on January 9 was one of several sources that are reporting 900 quakes since December 26th. While the frequency died down for a few days, it has become more active again. Friday's quakes are reported 27-29 miles SW of Cooke City-Silver Gate Montana, the largest 3.3.

The US Geologic Service was my source for the 7.5 quake in 1959. Wikepedia reports 7.3-7.5.

After going back to my sources, I have to stand by what I wrote . . .

I can't post links in the comments, but I will add to the blog itself.

I purposefully listed all of the kinds of activity that are possible - 1985 had a swarm of earthquakes as well. A hydrothermal explosion at an existing geothermal feature, a larger earthquake or quakes, or changes in activity at the current geothermal features are the most likely events to follow this swarm of earthquakes. So far, the reports I am reading do not seem to think that magma movement or lava flows are imminent.

JudeSecret said...

I agree it seems from My perspective the movement in the plates including subduction. magma, volcanos, steamers etc... Increases almost like the earth is taking care of itself and Sweating volcanic ash and magma causing a cooling effect like a nuclear winter type of thing or a mini ice age? Then as it cools, the plates get more stiff and unmoving causing further immobility in the earths crust, less subduction, less steamers, more snow in the air and on the ground which is reflecting solar rays back to the outer space. Also I must say that Yosemite's super volcano is about. to go critical! In light of the plates moving around the faults west of Oregon and the movement in the Midwests' Madrid fault and the. HIGHER Temperatures from Global Warming etc... Indicates Alarmingly to me that all the plates are becoming more active. Thus increasing the probability of world wide catastrophe not only from the earthquakes but the possability of Super volcanoes. I'm Not Too paranoid am I? I have been watching how the plates are moving and it seems to me that the movement on the west coast and mid america may have set up Yosemite to go Super. If the water levels change (drop or disappear) I'm running to the southern hemisphere to get a little extra time.
Jude Wilson

Mary Ann Melton said...

Hi, Jude. Thanks for your comment. I did some research to double check your information against what I had been seeing elsewhere.

There are some unusual quakes in California right now, but they are nowhere near Yosemite. The area around the Salton Sea has been recording swarms of earthquakes since last Saturday. Yosemite is an area created by vocanic activity, but the Caldera is at Long's Valley. I checked the status and everything is at normal there. The quakes at Yellowstone also died down, although there are still a few quakes, nothing like the swarm in January. If you go to the USGS Earthquake Center, you will note that there have been some kind of earthquake activity all around the Pacific Basin. When I checked this in January there were more quakes than now. Mount Redoubt in Alaska is currently erupting. Mount Cleveland farther west is still under a Yellow alert. It erupted briefly on January 2, 2009. Here is a link to info about that eruption: Eruption information.

While natural catastrophes are part of our planet's history, I don't think we are any greater risk right now based upon my research.

Anonymous said...

I have spent my whole life in Yellowstone, and feel it as a pressure release valve. Give or take 600 thousand years, I would rather go with mother natures action, than the killing devices of corrupt and evil humans.

Mary Ann Melton said...

Thanks for your comments, Anonymous! I don't think there is any place in the world immune from natural disasters of some sort. You are lucky to have lived your life in the Yellowstone area - such natural beauty and bountiful wildlife.