5 May 2018
6.9 Quake Rattles Hawaii’s Nerves as Kilauea Rumbles.
Posted by Dan Satterfield
The new NOAA 20 satellite captured this night-time visible light image of the eruption on the Big Island of Hawaii. From NOAA/CIMMS.
A 6.9 quake hit the Big Island of Hawaii Friday afternoon as lava fountains erupted in a housing development near Volcanoes National park. The NPS has now closed the park and the area has been evacuated. Kilauea is a shield volcano and not like Mt. St. Helens which is a strato-volcano. While a Strato-volcano can have an explosive eruption that throws ash miles into the air, shield types volcanos tend to produce large lava flows.
The big Island sits atop a “hot spot” in the mantle and volcanoes will erupt as the Pacific plate passes over this spot. The Big Island is now on top of this hot spot but Maui once was and so was Oahu. Looking at the direction of the Hawaiian Islands actually shows you the movement of the Pacific tectonic plate!
From here: https://pubs.usgs.gov/imap/2800/TDPback.pdf
These quakes indicate that magma (Lava that has not degassed at the surface) is moving and certainly a large quake like this is not good news. When was the last quake this big in Hawaii you ask? The answers to all of those questions are in an excellent pdf from the USGS and it’s worth a read here.
The image below from the USGS. Today’s 6.9 quake was in almost the very same spot as the last quake that was stronger, a 7.1 in 1975.
From the USGS on Friday.
The quakes around the volcano are happening at a frequency of about one per minute tonight with a mag 4 every hour or so! This certainly is worth paying attention to.
Note: We have some excellent geologists who blog here on the AGU Blogosphere and being a meteorologist, this is not my expertise. I know enough to know when to ask an expert. Check back here this weekend and I suspect some more info will be coming. Hopefully, this answers some of the basic questions.
Dan Satterfield has worked as an on air meteorologist for 32 years in Oklahoma, Florida and Alabama. Forecasting weather is Dan's job, but all of Earth Science is his passion. This journal is where Dan writes about things he has too little time for on air. Dan blogs about peer-reviewed Earth science for Junior High level audiences and up.
You imply that magma motion is responsible for everything that is happening at Kīlauea. That is not right. Hawaiian volcanoes are large, heavy, and weak. They bulge out sideways under their own weight. That bulging produces shear at the base where the edifice sits on the old sea floor, and tension in the upper surface. Any small creep at the base will increase the near-surface tension, perhaps opening up cracks that magma can invade (so explaining the down-rift migration of magma to Leilani Estates). The creep will also increase the loading on adjacent segments of the basal fault, possibly triggering a large basal-slip earthquake like the one on May 4.
Magma intrusion does produce small shallow earthquakes and tilt changes at the surface, but the great bulk of the work is not done by magma but by gravity.
They bulge out sideways under their own weight. That bulging produces shear at the base where the edifice sits on the old sea floor, and tension in the upper surface. https://7continents.guide/ Any small creep at the base will increase the near-surface tension, perhaps opening up cracks that magma can invade (so explaining the down-rift migration of magma to Leilani Estates)