Mount Hood, located in Cascade Volcanic Arc of northern Oregon, is a stratovolcano, a conical volcano built by layers of hardened lava, volcanic ash and other by-products of volcanic activity. Mount Hood is known to be a potentially active volcano, with the last eruption taking place around 200 years ago in the 1790s (not too long before the Lewis and Clark expedition) and a series of small streams and ash explosions occurring in the mid-1800s. However, this 500,000-year-old mountain rarely showed violent eruptions like Mount St. Helens, with only slow lava flows occurring in the past eruptions. While scientists assure that it is showing no signs of eruptions today, visitors frequently witness stream plume rising from the fumaroles, the opening of the volcano.
Glaciers and perennial snowfields are also important constituents of Mount Hood, covering approximately 13.5 km2. There are 11 major glaciers and one snowfield, with the largest glacier being the Eliot and Coe Glacier on the north flank of the mountain. Interestingly, the past lava flows during the last ice age influenced the distributions of these glaciers, and glaciers, in turn, provided water, the source of mobilization for lahars (destructive mudflows).
Currently, three volcanoes in Chile are restless, according to the Servicio Nacional de Geología y Minería. A “class yellow” status for these glacier-covered peaks means elevated seismic activity and higher potential for eruption.
One of South America’s most active volcanoes, Villarrica, erupted Tuesday, 3 March 2015, around 3 a.m. local time in Chile, creating a danger that lava would interact with the large ice cap on the mountain. The volcano spewed a lava fountain 1.5 kilometers into the air, and the pillar of smoke and ash reached 6-8 kilometers in height. Fortunately, the National Emergency Office issued a red alert and ensured the evacuation of roughly 3300 people from the volcano’s vicinity, especially residents from the town of Pucón. This area experienced many moderate to large eruptions, including events in 1640 and 1948 which appear in the historical record, and earlier ones attested to by indigenous populations of the area and by geological evidence.
The upper reaches of the volcano are covered by an ice cap about 40 square kilometers in area, including the Pichillancahue-Turbio Glacier. This 2840 meter-high mountain is a popular destination for hikers, who are fond of peering inside of the volcano. What differentiates Villarrica from many other volcanoes is that it contains an intermittent lava lake within its crater. In fact, Villarrica volcano is composed of layers of hardened lava and volcanic ash from previous eruptions. It is capable of erupting explosively due to high pressure that results from the release of dissolved gas as magma rises to the surface. These explosions are often accompanied by loud sounds that can be heard over great distances.
The eruption can be seen in this dramatic time-lapse video, which starts in black and white, and then shifts to color.
There are three major interrelated concerns about this eruption. Firstly, the lava could melt the glacier ice and snow on the sides of the volcano, causing massive lahars (mud and debris flows), much like the ones that occurred during the eruptions of 1964 and 1971. Secondly, the noxious volcanic ashes could pervade in the air. During the 1971 eruption of Villarrica, at least 15 fatalities from the inhalation of toxic gasses were reported. Finally, there is a somewhat lower risk of a large releases of volcanic ash, which could affect human health, damage power transmission lines, and harm vegetation. Previous eruptions of Villarrica have released smaller amounts of ash; paradoxically, these have protected the glaciers by insulating them and protecting them from incoming solar radiation.
At the time of posting, the volcanic activity is diminished, with much reduced lava emissions and lesser seismic activity. Alerts remain at the orange level for the present.
For other stories on volcanic eruptions near glaciers, look here and here
Mount Aragats, a 13,435 ft mountain peak in northwestern Armenia, is located to the northwest of Armenia’s capital city of Yerevan and north of the Ararat Plain. There is no doubt that it is the highest mountain in Armenia, which places it on the World Country High Points peak list. Aragats is a large circular andesitic-to-dacitic stratovolcano that consists of both lava and tufa. The crater of the volcano has turned into a cirque of a glacier, and contains some other small glaciers as well. Several striking photographs of Aragats Glaciers are shared below.