Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12 Page 13 Page 14 Page 15 Page 16 Page 17 Page 18 Page 19 Page 20 Page 21 Page 22 Page 23 Page 24 Page 25 Page 26 Page 27 Page 28 Page 29 Page 30 Page 31 Page 32 Page 33 Page 34 Page 35 Page 36 Page 37 Page 38 Page 39 Page 40 Page 41 Page 42 Page 43 Page 44 Page 45 Page 46 Page 47 Page 48 Page 49 Page 50 Page 51 Page 52 Page 53 Page 54 Page 55 Page 56 Page 57 Page 58 Page 59 Page 60Yellowstone caldera Earthquakes and landslides 19 The 7.3 magnitude Hebgen Lake earthquake in 1959 was centered just outside ofYellowstone in Montana, but was also the largest recorded earthquake (magnitude 6.5) in Wyoming. The earthquake disrupted some of the thermal features inYellowstone. New geysers began to erupt, and others changed eruption times. By measuring seismic waves from earthquakes, scientists estimated that the magma chamber underneath theYellowstone caldera is 55 miles long, and could potentially erupt with a force about 2,000 times the size of the Mount St. Helens eruption in 1980. Yellowstone last erupted approximately 640,000 years ago. Landslides are one of the most common geologic hazards in Wyoming. Most landslides occur in mountainous areas where precipitation (rainfall and snow) is much greater than in the basins and plains. The GrosVentre landslide (pictured to the left) occurred on June 23, 1925, following weeks of heavy rain and melting snow. Fifty million cubic yards of rock swept across the GrosVentre river, forming a natural dam. The dam lasted for two years before breaking up, causing a massive flood that killed six people downstream. GrosVentre landslide Historical landslide activity Other landslides Earthquakes (1890–2014) Moment magnitude scale 5–6.5 Less than 3 3–4.9 Data Go Interactive