Alaska's Mount Spurr Shows Signs of Potential Eruption

An active volcano near Alaska's most populated city could be on the brink of eruption, according to scientists who are constantly monitoring a potential threat.

Signs of unrest at Mount Spurr -- located in the Aleutian Arc in southern Alaska about 75 miles west of Anchorage -- have increased over the past 10 months, according to volcanologists at the U.S. Geological Survey.

Small earthquakes have been occurring above ground at Mount Spurr since April, leading to odds of eruption of about 50%, Matthew Haney, scientist in charge of the Alaska Volcano Observatory in Anchorage, told ABC News. In addition, the surface of the volcano is inflating or swelling, with GPS sensors measuring about 2.5 inches of outward motion, he added.

Snow and ice at the summit of Mount Spurr are also starting to melt, which are clear indicators of increasing unrest, Haney said.

The last time Mount Spurr erupted, in 1992, similar earthquake activity occurred for about nine months before eruption, Haney said.

The volcano alert level for Mount Spurr as of Friday morning was at a watch, according to the USGS, meaning the volcano is exhibiting heightened or escalating unrest with increased potential of eruption, although the timeframe is uncertain.

Due to its proximity to the most populated city in Alaska, volcanologists are constantly monitoring for potential threats from the stratovolcano, a steep-sided volcano comprised of hardened lava and tephra.

There are 11 remote seismic stations situated around Mount Spurr. Once the researchers begin to detect volcanic tremor -- a continuous shaking that can last for several minutes rather than short, small earthquakes -- they will likely raise the alert level because it is a "clear indication" that unrest is increasing, Haney said.

The 1992 eruptions began in June of that year following about three weeks of volcanic tremor, Haney said.

The 11,070-foot volcano experienced three eruptions in 1992. During the August 1992 event, an eighth of an inch of volcanic ash dusted the city of Anchorage, carried there by an eastward wind event, Haney said. The last eruption occurred in September 1992.

While the ash was mostly a nuisance for the majority of residents, the Anchorage airport was forced to shut down for 20 hours as a result of the wind and ash event.

"You do not want ash in modern jet engines," describing the airport closure as a "big disruption."

Mount Spurr also erupted in 1953, leading to a quarter-inch of ash blowing into Anchorage, Haney said.

It is considered one of the highest-threat volcanos out of the dozens in Alaska due to its proximity to Anchorage and ability to potentially disrupt or endanger daily life for residents, Haney said.

But it's just as likely that an eruption could not occur, Haney said.

Several months of unrest at Mount Spurr in 2004 did not lead to an eventual eruption, Haney said. In 2012, the volcano rumbled again but did not erupt.

In the most recent event, there has not been any indication that volcanic gas is being emitted in the region, which adds to the uncertainty, Haney said.

"We're still diagnosing what is happening inside of Mount Spurr," Haney said.