If youâ€™ve been reading Volcano Watch or following the news from Washington State, you know that Mount St. Helens began erupting in early October 2004 for the first time in 18 years. What you may not know is that Mount St. Helens is still erupting, and at a rate roughly equivalent to that of Kilauea, or a truckload of lava every second. At right are are shaded-relief maps that illustrate the changes that have occurred as a result of the current eruption in the crater of Mount St. Helens.
One image shows the crater as it looked in 2003. The steep, horseshoe-shaped crater rim, which formed during the catastrophic eruption of May 18, 1980, surrounds a circular, rough lava dome that grew between 1980 and 1986 as sticky, viscous lava erupted onto the crater floor. That dome covers roughly the same area as Halema`uma`u Crater (in Kilauea caldera). The smooth surface between the 1980-86 lava dome and the crater wall is a glacier that has been growing since 1986 â€“ the youngest glacier in the United States.
The other image shows how the crater looked on December 11, 2004, three months after the start of the current eruption. Now, where there was once only ice, there is a new lava dome roughly one third the volume of the old one! And the eruption shows no sign of slowing down. Earthquakes have been continuing at a constant rate since mid-October 2004, and GPS measurements from equipment placed by helicopter onto the cooled portions of the lava dome have shown a continuous extrusion rate since that time.
With the persistence of the activity at Mount St. Helens, a common question is â€œHow long will this eruption last?â€ Like Kilauea, which has been erupting lava since 1983, the current activity at Mount St. Helens could continue for decades. Santa Maria Volcano, located in Guatemala and very similar in composition to Mount St. Helens, is host to a lava dome that has grown without pause since 1922. If the eruption does persist at its current rate, then in 30 years, the volume removed by the 1980 landslide would be completely replaced, and Mount St. Helens might once again resemble the snow-capped peak that existed before 1980. This rapid change in the surface of the land, though common in Hawai`i (where pounding surf and erupting volcanoes bring about major changes on a daily basis), is relatively rare on the mainland and will be the subject of intense study by scientists for years to come.
Eruptive activity at Pu`u `O`o continues. At least five of the vents inside the Pu`u `O`o crater have been spattering frequently since February 1, producing a bright glow from the crater on clear nights. Thus far, the crater vents have not produced any lava flows but have built several new spatter cones. The MLK vent area, at the southwest base of the cone, intermittently erupts small pahoehoe flows that stack up close to the vent.
The PKK flow continues to host substantial breakouts from the 2,300-ft elevaton to the coastal plain. Lava is entering the ocean at both West Highcastle and at Ka`ili`ili. The closest activity to the end of Chain of Craters Road, in Hawai`i Volcanoes National Park, is at West Highcastle, 2.6 km (1.6 mi) from the ranger shed. Expect a 1-to-1.5-hour walk each way and remember to bring lots of water. Stay well back from the sea cliff, regardless of whether there is an active ocean entry or not. Heed the National Park warning signs.
During the week ending February 9, one earthquake was felt on Hawai`i Island. The magnitude-3.0 quake was located 5 km (3 miles) south of Pu`u `O`o at a depth of 9.3 km (5.8 miles) and was felt at the Volcano Golf Course.
The swarm of earthquakes beneath Kilauea summit reported last week seems to be over. It was accompanied by at least 2 cm (an inch) of southward movement of the southern flank of Kilauea.
Mauna Loa is not erupting. The summit region continues to inflate. Since July 2004, the rate of inflation and number of deep earthquakes has increased. Weekly earthquake counts have varied from 5 to over 150 but have been less than 10 since the beginning of the year. During the week ending January 27, six earthquakes were recorded beneath the summit area. Nearly all are 30 km (18 mi) or more deep, and most are the long-period type, with magnitudes less than 3.
This article was written by scientists at the U.S. Geological Survey’s Hawaii Volcano Observatory and is republished by HawaiiNews.com with permission.