This is the monthly volcano report for December 2019. If you already know what this usual intro says, please click the title of this post or “read more” to continue. The reported earthquake counts are taken directly from the U.S.G.S. and are only earthquakes reported, not earthquakes recorded. Regarding earthquake counts, it is likely that the reported earthquake total for a given location and time period, mostly during earthquake swarms, is lower than the actual count of earthquakes, in certain cases sometimes drastically lower. Remember, most earthquake swarms at volcanoes do not lead to eruptions. However, almost every eruption is preceded by some type of earthquake swarming and surface deformation. Therefore, swarms and deformation should always be monitored closely regardless of where you think the activity is headed.
The volcanoes I will be doing monthly updates on are Yellowstone Caldera in Wyoming, Long Valley Caldera in California, Newberry Caldera and Mt. Hood in Oregon, Mt. Rainier and Mt. St. Helens in Washington state, and Mt. Shasta and Lassen Peak in California. In this update, we will look at reported seismicity counts. If you wish to see recent deformation for Yellowstone or Long Valley, please head to the “Deformation Updates” page which is updated every 2 months or so.
The time period of the reported seismicity counts for this update, derived from the USGS earthquake catalog, is from 00:00UTC Dec. 1, 2019 through 23:59UTC December 31, 2019 and magnitudes are always going to be -1.0 and above so you will see every single earthquake that was reported for this time period. The smallest earthquake ever recorded was a M-1.0 and the largest earthquake ever recorded was a M9.5. Also, the coordinate box I use for each volcano is exactly the same every month, so you always see the activity that occurred in the same area every month. Regarding the 3-plot seismic images I generate for the largest events, I will always try my best to use the closest seismic station to any given event. I will also add the link to the USGS EQ map showing the locations of reported seismicity for the location and time period in question.
December 2019 was another mediocre month for seismicity at Yellowstone. Except for a few magnitude 3s and some very short and energetic swarming, this month was boring. Regardless, we did see some interesting earthquakes including a few M3s which were the largest to strike this region in a few years. Only 93 earthquakes were located during December. A few other small events may not have been reported, but seismicity was generally low for this month.
The largest earthquake this month was a M3.5 at 17km in depth on Dec. 15, 2019 at 12:32UTC. It struck just barely outside of the western border of Yellowstone National Park, just 25km WSW of Old Faithful Geyser. It was the largest to strike Yellowstone since a M3.6 struck Maple Creek on July 18, 2017. December's M3.5 was reportedly felt by 5 people which is quite the achievement since there are hardly any people, if any at all, in this area during this time of year. The plots directly below are of this event:
Surprisingly, there was also a M3.4 on this same day. It was the largest earthquake for December 2019 to strike within the caldera itself and is likely the largest earthquake to strike the caldera itself in many years. It struck at 4.0km in depth just 10 hours prior to the event shown above. The epicenter was very close to Mary Lake. Directly below are plots of this event. Notice the strange spectrogram signature at the start of the event:
Steamboat Geyser, the largest active geyser in the world at Norris, remained active through the month of December 2019. It erupted a total of 3 times during December. The last eruption of this month, and for all of 2019, was the 48th eruption which occurred at 04:34UTC on December 27, 2019 (9:34pm Mountain Time, December 26, 2019). The grand total of eruptions during the 2018-2019 is 80 eruptions! That is alot! Plots shown directly below are of the last eruption of 2019:
Long Valley Caldera
During the month of December 2019, there were 373 earthquakes for the Long Valley Caldera region. That is the lowest count since June 2019! Seismicity continues to decline every month now since the intense swarming seen in September (CLICK HERE to see information about that). However, the decline can only go on for so long and another period of unrest similar to that seen in September is almost certain.
The largest earthquake to strike Long Valley in December 2019 was a M3.6 at 9.9km in depth on December 26, 2019 at 19:48UTC. It struck along the southern rim of the caldera just 13km W of Toms Place, CA. Over 161 people felt this event which was originally labeled a M4.0. Plots directly below are of this event:
Although October and November saw no seismicity, December 2019 saw 2 reported events. Both contained high frequencies and low frequency activity still has not reemerged since it dwindled away in the summer of 2019.
The largest event for Newberry Caldera for December 2019 was a M0.5 "Other Event" supposedly at -1.7km in depth. It struck under the NE base of Newberry Caldera under N Paulina Lake Rd. on December 28, 2019. I am unsure why it was labeled as "Other Event". You can clearly see in the plots below that this appears to be a normal high frequency earthquake (however there are some slightly stronger lower frequencies):
The only other earthquake to strike Newberry in December was a M0.3 at 4.0km in depth on December 16, 2019 at 20:30UTC. It struck around 5 miles NW of Newberry directly under the Lava Cast Forest. Directly below are plots of this micro-quake:
Although Mt. Rainier is still within normal background levels, this volcano saw its highest monthly count in over 6 months. There were 35 earthquakes located for December 2019. Only a few were scattered around the perimeter and most events this month occurred under the edifice of the volcano. This isn't a major increase in anyone's standard, but it is interesting nonetheless!
The largest earthquake to strike Mt. Rainier in December 2019 was a M1.4 at 1.5km in depth on December 19, 2019 at 21:02UTC. It struck directly beneath the volcano. Below are plots of this event:
Mt. St. Helens
December 2019 was a very calm month for one of the most active volcanoes in the United States. Mt. St. Helens saw only 11 earthquakes during this month. This was likely one of the calmest months in 2019 for this volcano.
The largest earthquake to strike Mt. St. Helens was a M0.8 at 10km in depth on December 10, 2019 at 06:25UTC. It struck about 5 miles SW of the summit. Plots below are of this event:
During December 2019, Mt. Hood experienced only 3 earthquakes. Seismicity has returned to background levels since the large spike in seismicity in July 2019 (CLICK HERE for information on that crazy swarm). This month saw two earthquakes strike under the edifice and one small micro-quake to the SW near the epicenter of the July swarming.
The largest event of December 2019 for Mt. Hood was a M2.4 at 1.9km in depth on December 9, 2019 at 01:00UTC. It struck directly under Mt. Hood. This earthquake was the largest one to strike Mt. Hood since the M2.8 at 6.8km in depth on Oct. 10, 2017. Not even the largest swarm in this area, which occurred July 2019, had an earthquake this large. Regardless, Mt. Hood remains in background levels. Below are plots of the largest event of December 2019:
Seismicity has continued to decline dramatically since one of the largest swarms in decades struck Mt. Shasta in September 2019 (CLICK HERE for more information about that). Only two earthquakes were located for Mt. Shasta during the month of December and they both were about 7 miles north of the summit. The largest was a M0.8 at 1.3km in depth on December 2, 2019 at 03:38UTC. Plots below are of this event:
Lassen Volcanic Center
Lassen Volcanic Center was very calm this month as well with only 11 earthquakes being located for December 2019. The largest was a M1.7 at 5.9km in depth on December 5, 2019 at 16:10UTC. It struck about 10 miles east of Lassen Peak. Plots below are of this event:
I used to create monthly volcano updates as videos for my YouTube channel and my website. However, that took far too much time and I have had to discontinue those updates. That being said, I will now do monthly volcano updates via this blog here. I will try to get them out as soon as possible. However, if I am very busy, they may be as much as 1-2 weeks late.