Geology QuestionsWhere is the volcano?After driving past miles of rugged lava flows, you may have arrived here expecting a gigantic volcano with steep slopes and a crater at the summit like Mount St. Helens. The volcanoes at Craters of the Moon do not fit that description. The eruptions here, called "fissure eruptions", occurred along cracks in the earth's crust. This series of cracks extends over 52 miles across the park, creating an area known as the Great Rift. The eruptions were of very fluid basaltic lava from which gases could easily escape. Without high gas pressure, eruptions tend to be very mild and produce small cinder cones and extensive lava flows. There are more than 25 cinder cone volcanoes at Craters of the Moon. When did the eruptions occur?Volcanic activity has occurred on the Snake River Plain for many millions of years. The much younger lava flows at Craters of the Moon were formed by eruptions that started only 15,000 years ago and represent the last period of active volcanism in the area. The most recent activity occurred approximately 2,100 years ago. Parts of the youngest lava flows can be viewed at different places along the Loop Road or hiking trails. Will the volcanoes erupt again?Craters of the Moon is considered dormant, not extinct. Signs of impending eruptions (earthquakes, the opening of steam vents, and ground swelling) have not occurred recently. However, geologists believe that the area will become active again within the next 900 years. Where can we see the craters?Although a few craters can be seen from the highway (such as North Crater), most require at least a short hike to view. Some cinder cones, like Inferno Cone, do not have a visible crater. The most accessible craters are those at the Spatter Cones, which require a 0.1 mile walk from the parking lot to view. The trail to Snow Cone is also fully accessible. The crater of Broken Top is visible near the beginning of Broken Top Loop Trail. If you are prepared, Big Craters, three large, neighboring craters, is a short, steep hike from the Spatter Cones parking area on North Crater Trail. For your safety, off-trail travel is not permitted at the Big Craters or Spatter Cones areas. Where can we see the Great Rift?The line of cinder cones that extend from the Loop Road to the southeast show the route of the Great Rift because they formed along it. This line is most obvious when viewed from the top of Inferno Cone. In many places, you could be standing on the Great Rift and not realize it. There are no places along the Loop Road or highway where you can look into the Great Rift. What is that big mountain east of the park?East of Craters of the Moon is Big Southern Butte. It was formed when two rhyolitic lava domes combined to create a 2,380 foot high mountain. Big Southern Butte is estimated to be about 300,000 years old and is not part of the park or related to the eruptions here. Two smaller lava domes, Middle Butte and East Butte, are located east of Big Southern Butte.
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Last updated: October 31, 2024