Shake Rattle and Roll

December 4th, 2014

If you lived or were visiting north-central Arizona around Thanksgiving 2014, you might’ve been surprised to experience an earthquake. Centered about 7 miles north of picturesque Sedona, the 4.7 temblor provided enough jolt that people knew it was happening, and they felt it as far away as Flagstaff. Flagstaff is situated just under  30 miles north of Sedona, so roughly 23 miles from the quake’s center. It happened late on a Sunday night, with over 1200 people reporting to the US Geological Survey (USGS) that they felt the shaking.

You might have thought it had to be a fluke. You’d be wrong.

Arizona has been home to quakes before, in various parts of the state. The largest measured on record was a 5.6 in the 1950’s, but there was a swarm of temblors in the early 20th century that ranged up as high as magnitude 6.2. Those hit areas near the Utah border. There were no deaths or injuries, though the shock was powerful enough to rip a 50-mile rift in the earth’s surface and damaged homes as far south as the town of Williams.

In fact, the USGS says they record 10-15 small quakes every month in Arizona, most of which are so small you’d never notice them. Even the Phoenix metropolitan area isn’t immune. On September 20 of this year, a 3.4 magnitude was recorded in the vicinity of Apache Junction. There wasn’t a report of anyone in the vicinity who felt it.  Ten years ago, give or take, a series of shocks rocked the Winslow area, including a recorded 5.1 event. in 2005, a couple of magitude 4+ earthquakes rumbled through an area near Payson.

You get the picture. This state may not be famous for its earthquakes, but scientists say we’ve got some fault lines capable of producing up to a 7 magnitude event. That’s a pretty significant tremor!

Part and parcel with the quakes come volcanoes. Arizona’s last eruption pre-dated Mt. St. Helens by a ways. Sunset Point, a ridge west of I-17 between Phoenix and Flagstaff, underwent a major eruption in AD 1064. In fact, some 1800 square miles of north-central Arizona lies in a field of volcanic activity, though most eruptions have been small and situated in the distant past. The San Francisco Peaks recreational area, the highest point in the state, is a dormant stratovolcano. On a drive from Oak Creek to Flagstaff, you can see the gray-green markers of magma vents rising up through the cliffs. That’s not Arizona’s only place in volcanic history. To the east of Phoenix lies the mining communities of Globe and Miami, and still further east of them the San Carlos Apache Indian Reservation. Native Americans harvest a significant portion of the world’s gemstone-quality peridot on the reservation, digging it out of hollow lava tubes.

A caution here. If you’re not a member of the Apache tribe, don’t expect to go prospecting on the reservation. You will not be welcome and may be arrested – or worse.

With the uptick in earthquake activity, does that mean we’re in for a resurgence of volcanic activity as well? That’s tough to call. Certainly an eruption 1000 years ago is recent enough to pay attention, though it’s doubtful it’ll spring to life without any warning. Arizona’s Geological Survey (azgs.az.gov) keeps tabs on the state’s seismological activities from their offices in Tucson. In general, nobody’s raised a red alert – or orange or yellow – so it seems pretty unlikely. Then again, Mother Nature has a tendency to thumb her nose at the predictions and assumptions of we puny humans. So maybe the answer should be, “We shall see.”