Earth science: fundamentals and applications

Earth Science

Ring of Fire

Ring of Fire originally aired on the National Geographic Channel in August, 2007 as part of the Naked Science series produced by Ben Fox and Ian Hunt. The hour-long Ring of Fire program focuses on scientific efforts to understand the danger posed by the 25,000-mile long chain of volcanoes and earthquakes that makes up the Ring of Fire. The video explores scientific explanations for a rise in volcanic activity throughout the Ring of Fire, and discusses ways of predicting future volcanic eruptions, earthquakes, and tsunamis.

The Ring of Fire is a horseshoe shaped region surrounding the Pacific basin that comprises 90% of the world's volcanoes, and 80% of the world's largest earthquakes. The Ring of Fire is associated with a nearly continuous series of oceanic trenches, island arcs, and volcanic mountain ranges and plate movements. It is also known as the Pacific Ring of Fire, Circum-Pacific belt or the Circum-Pacific seismic belt (Crystalinks, 2011).

Plate tectonics and the movement and collision of crustal plates are responsible for the Ring of Fire, including two areas that the video Ring of Fire focused on, the Pacific northwest and Japan. A portion of the Pacific plate, along with the small Juan de Fuca plate, is being subducted beneath the North American plate. Further west, the Pacific plate is being subducted along the Kamchatka-Kurile Islands arcs south of Japan (Crystalinks, 2011).

The Ring of Fire is also home to one third of the global population. The video describes a series of scientific discoveries that indicate drastically increased volcanic and seismic activity in this region. New York University scientist Mike Rampino studied ice core samples covering an 11,000-year period from the U.S. National Ice Core Lab that revealed significantly higher levels of sulfur dioxide. These findings could only result from volcanic eruptions, with the samples clearly showing an increase in volcanic activity of 300% over the past two thousand years.

The video also explored recent tectonic activity in several fault areas. Scientists in the video focused on the Cascadia fault, a 680-mile long area located about 50 miles off the Pacific coast. The area covers the Pacific northwest and includes nearby Portland, Vancouver and Seattle. The Cascadia fault was thought to be tectonically dead, with no recorded activity over the last 300 years.

However, USGS geologist Brian Atwater examined soil samples from a salt marsh along the Copalis River in Washington that clearly showed evidence of a tsunami, with sand deposits and seawater inundation killing the spruce forest in the area. Coincidentally, local Native American legend described the activities of a Thunderbird, which scientists now interpret as an oral history of a megaquake. By comparing notes with Japanese scientist Kenji Satake for what had previously been recorded as an orphan tsunami, the scientists were able to establish the earthquake and resulting tsunami as occurring in January of the year 1700.

The Ring of Fire video also discussed scientific attempts to understand the significance of recent earthquake activity and its causes in hopes of predicting when the next megathrust earthquake might strike the area. One possible cause of earthquake activity might be sea level changes that put additional pressure on the earth's crust, thereby triggering volcanic eruptions. With no clear ability to forecast either the timing or magnitude of the next big quake, scientists are left to depend on seismic wave sensors to provide a few seconds or minutes warning for such densely populated areas as Japan and the Cascadia fault region.

Scientists may not know when the next megathrust earthquake will strike in the Cascadia subduction zone, but most agree it's just a matter of time. After having been dormant for 300 years, the last rupture unleashed the largest known earthquake to strike the Lower 48, a magnitude-9 quake that sent tsunami waves crashing into Japanese coastal villages. The Associated Press quotes Brian Atwater as noting that the Pacific Northwest "has a long geological history of what happened in Chile. It's not a matter of if but when the next one will happen." Atwater was comparing the Cascadia fault to the one that broke offshore Chile in 2010, triggering a magnitude 8.8 quake (Chang, 2010).

According to calculations by Chris Goldfinger, head of the Active Tectonics and Seafloor Mapping Laboratory at Oregon State University, there is an 80% chance that the portion of the fault off southern Oregon and Northern California would break in the next 50 years and produce a megaquake. The odds of rupture are lower for the northern end, with a 27% chance during the same time period (Chang, 2010).

Natural Resources Canada (2011) presents similar arguments as the Ring of Fire video concerning megathrust earthquakes in the Pacific Northwest. While none have been observed in the short, approximately 150-year written history of the west coast of Canada, the article cites similar compelling evidence that they have occurred in the past. They too cite observations that include buried tidal marsh or coastal forest soils pointing to sudden land subsidence of approximately one meter that happened at the same time from Vancouver Island to Northern California.

All scientists find it challenging to predict the next Pacific Northwest megaquake. One of the largest earthquakes in history occurred during the January night in 1700 that ruptured the seafloor off Oregon and Washington. Within minutes of the magnitude-9 earthquake, a 30-foot wall of water inundated coastal areas, and within 12 hours the tsunami crossed the pacific and flattened houses along the eastern coast of Japan. Scientists believe the Northwest is due for another devastating megaquake (Rojas-Burke, 2010).

While precise predictions are impossible to make, scientists believe that by reconstructing the history of megaquakes in the Northwest, they have found a pattern that could help improve forecasts of the next big quake. Findings suggest that the largest, most damaging quakes may occur in cycles separated by 1,000-year periods of inactivity (Rojas-Burke, 2010); however scientists disagree over clustering in cycles as well as the length of inactive periods.

Earthquakes arise from the collision of massive sections of the earth's crust called tectonic plates. From Northern California to British Columbia, the Juan de Fuca Plate is plunging beneath the North American plate. This region, known as the Cascadia subduction zone, produced the volcanic peaks of the Cascade Range and it poses an ominous earthquake hazard. Scientists have arrived at various estimates of the near-term probability that a magnitude-9 megaquake will strike the Northwest. The most frequently cited number is a 10 to 15% likelihood over the next 50 years (Rojas-Burke, 2010).