Sand Mountain Volcanic Field facts for kids
Quick facts for kids Sand Mountain Volcanic Field |
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View down the north–northeast alignment of the Sand Mountain Volcanic Field, with Mount Jefferson visible in the distance
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| Location | Oregon, United States |
| Coordinates | 44°23′N 121°56′W / 44.38°N 121.93°W |
| Range | Cascade Range |
| Elevation | 5,459 feet (1,664 m) |
| Geology | Volcanic field |
| Age | Holocene |
| Volcanic arc/belt | Cascade Volcanic Arc |
| Last eruption | 2,000 years ago |
The Sand Mountain Volcanic Field is a special area in Oregon, United States. It is a group of volcanoes and lava flows. You can find it in the upper McKenzie River area. This field is part of the Cascade Volcanic Arc, a chain of volcanoes. It sits southwest of Mount Jefferson. It is also northwest of Belknap Crater and Mount Washington. The highest point in the field is about 5,463 feet (1,665 m) tall.
The Sand Mountain Field has been active for a long time. It started erupting about 4,000 years ago. The field has 23 cinder cones, which are cone-shaped hills made of volcanic rock. It also has many lava flows. These come from 42 different spots, lined up in two main rows. All the rock that erupted from this field would fill about 0.22 to 0.29 cubic miles (0.92 to 1.21 km3). The field also has a large area of tephra (volcanic ash and rock bits). There is even a lava tube system, which is like an underground tunnel made by flowing lava. Scientists think it's possible for the field to erupt again. But the risk from this specific field is considered low.
This volcanic field is inside the Willamette National Forest. It is close to Santiam Pass. Some parts of the field have forests. Trees like Douglas fir and western hemlock grow well here. This is because the tephra from eruptions makes good soil. People have even dug up volcanic rock (called scoria) from one of the cones. They use it for building roads. Nearby, you can visit a ski resort, Tamolitch Falls, and Clear Lake.
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Where is the Sand Mountain Volcanic Field?
The Sand Mountain Field is part of the Cascade Volcanic Arc. It is located in central Oregon, in the United States. This area covers about 29 square miles (76 km2). Its highest point is 5,463 feet (1,665 m) high. The field is inside the Willamette National Forest. It is near Santiam Pass. It lies southwest of Mount Jefferson. It is also northwest of Belknap Crater and Mount Washington.
The field is next to Clear Lake. This lake is where the McKenzie River begins. Lava flows from the Sand Mountain field actually blocked a river. This created the lake long ago. Clear Lake is about 148 acres (0.60 km2) big. It has a shallow northern part and a deeper southern part. The deepest spot is about 175 feet (53 m). Other lakes nearby include Lost Lake, Lava Lake, and Fish Lake. Fish Lake sometimes dries up in the summer. It was also formed by lava flows from Sand Mountain about 3,850 years ago.
The way the land is shaped here affects how lava flows. Lava usually flows downhill to the west. Wind also carries volcanic ash (tephra) to the northeast. The Oregon Cascades get a lot of rain and snow. About 80 percent of it falls in winter. This snow melts and seeps into the ground. It then comes out as springs years later.
Nature and Wildlife
Some parts of the Sand Mountain field have old, grown-up forests. But other areas with newer lava are mostly bare. The forests grow where lava flows have been covered by volcanic ash. This ash creates soil for the trees. Areas without ash have very little plant life. Below 4,300 feet (1,300 m), the forests are like those in the Pacific Northwest. They have lots of Douglas fir and western hemlock trees. There are fewer western red cedar trees here than in other Pacific Northwest forests. Wetlands called fens are around Lost Lake. This lake is about 3.1 miles (5 km) north of the field.
Inside Clear Lake, there is a special submerged forest. You can see Douglas fir trees standing upright under 120 feet (37 m) of water. The water is very cold, which helps keep them preserved. Scientists studied these underwater trees in 1965. They found that the trees were "drowned" about 3,000 years ago. This happened when a lava flow from Sand Mountain created Clear Lake. The eruption changed the area. It created new places for plants and animals to live. Today, Clear Lake has fish like brook and cutthroat trout. Rainbow trout are also added to the lake each year.
How the Volcanoes Formed
The Cascade Range and Cascade Volcanic Arc were formed by huge movements of Earth's plates. The Juan de Fuca Plate is sliding under the North American tectonic plate. This process is called subduction. In central Oregon, there are two main parts of the Cascades. The Western Cascades were active from about 35 to 5 million years ago. The High Cascades have been active for the past 5 million years. As the North American Plate slowly turned, the volcanic activity moved. It moved east in central Oregon.
The High Cascades area is like a sunken valley, called a graben. It is about 19 miles (30 km) wide and 1.2 to 1.9 miles (2 to 3 km) deep. Most of the lava here is mafic. This means it is rich in magnesium and iron. About 14 cubic miles (60 km3) of magma has erupted here in the last 15,000 years. Many of the volcanoes here are scoria cones.
The Sand Mountain Volcanic Field formed when magma pushed through cracks in the rock. These cracks were caused by the sinking of the High Cascades graben. The magma first came up as dikes, which are like walls of rock. Then it moved to the surface through different vents. The first magma was basaltic. Later, it changed to basaltic andesite. Eruptions at Sand Mountain came from two or three magma chambers.
The Sand Mountain Volcanic Field has 23 basalt and basaltic andesite cinder cones. It also has many lava flows. These came from 42 different spots. They are lined up in two main rows that go north to south. These lines suggest there are complex volcanic dikes under the field. Sand Mountain is the biggest cinder cone. It is 820 feet (250 m) tall. The field has six main groups of volcanic vents. These are the Central Group, Little Nash Crater, Lost Lake Group, Nash Crater, Sand Mountain Cones, and South Group.
Special Features
The Jack Pine cone in the Sand Mountain Field is unique. It is made of a rare type of rock called absarokites. This suggests it came from a different magma chamber.
Little Nash Crater has basaltic andesite lava. This lava is about 2,590 years old. Lava from the Lost Lake cone group is about 1,950 years old. At Nash Crater, the lava is basaltic andesite. The main Sand Mountain lava varies from basalt to basaltic andesite. These flows are between 3,850 and 2,750 years old.
The field also has a large area of volcanic ash (tephra). It covers about 59 square miles (154 km2). It has a volume of 0.094 cubic miles (0.39 km3). This tephra field is much bigger than others from similar volcanoes. The ash bits are very fine. They are between 0.0049 inches (125 μm) and 0.020 inches (0.5 mm) in size. These ash deposits are between 3,440 and 1,600 years old. They can be over 6.6 feet (2 m) thick, even 5.6 miles (9 km) away from the Sand Mountain cinder cone. Scientists think the lava from Sand Mountain mixed with water. This likely came from groundwater.
There is also a lava tube system called Lucy's Cavern. It is at least 490 feet (150 m) long. It goes down 26 to 33 feet (8 to 10 m) deep. There are also two round "vertical pits." These are called Century and Moss Pits. They are 62 feet (19 m) and 98 feet (30 m) deep. Moss Pit is 8 feet (2.4 m) wide at the entrance. Century Pit is 3 feet (0.91 m) wide at its entrance.
When Did Sand Mountain Erupt?
Volcanic activity in this area has been strong since the glaciers melted. This started about 7,700 years ago. It is one of the youngest volcanic areas in the Cascade Arc.
The last eruption at Sand Mountain Volcanic Field was about 2,000 years ago. This happened at the Lost Lake cinder cone group. Before that, about 3,000 to 4,000 years ago, lava flows erupted. They moved west and blocked rivers, creating small lakes. Past lava flows from Sand Mountain and Belknap Crater changed the McKenzie River. They created waterfalls like Sahalie Falls and Koosah Falls. They also formed the 1.5-mile (2.4 km) long Clear Lake. This lake still has tree branches from the time of the eruption.
The total amount of lava and rock from the field is estimated to be 0.22 to 0.29 cubic miles (0.9 to 1.2 km3).
Scientists used paleomagnetic dating to learn more. They found that the field had at least 13 different eruptions. These happened over a short time, maybe just a few decades, about 2,950 years ago. The Jack Pine vent, at the northern edge, is different. It likely erupted about 4,000 years before the rest of the field. Some scientists think Jack Pine erupted about 7,000 years ago. The main Sand Mountain eruptions happened around 3,000 years ago.
One eruption around 950 BCE was very powerful. Another eruption at Jack Mountain around 5050 BCE was also strong. The eruptions at Sand Mountain Field were explosive. But they were different from typical Strombolian eruptions. They were sustained for a long time. This was likely because the lava mixed with water.
About 3,850 years ago, the Nash Crater cinder cone erupted. Its lava flowed west. It blocked a stream and created Fish Lake and Lava Lake. These lava flows were rough and had no plants growing on them. The Lost Lake cinder cones erupted about 1,950 years ago. These eruptions blocked the Lost Creek tributary. This formed Lost Lake.
What About Future Eruptions?
The Sand Mountain Field is about 62 miles (100 km) from a city with 500,000 people. It is also near a main road and a popular ski area. So, future eruptions could affect many people. Lava flows might reach highways. But most lava in this area is unlikely to block roads. Volcanic ash (tephra) from Sand Mountain could travel over 6.2 miles (10 km) from the volcano. If lava flows reach forests, they could start forest fires. However, the risk from this field is considered "Low/Very Low."
Volcanoes in the nearby Cascades Range will likely erupt again. There are signs of magma moving under the Three Sisters volcano. This could lead to eruptions. New eruptions might create new cinder cones, like those at Sand Mountain. Also, dangerous volcanic gases could build up after an eruption. These include sulfur dioxide, hydrogen chloride, and hydrogen fluoride.
People and the Sand Mountain Area
The upper McKenzie River area is important for studying geology. The first research here was in 1929. More maps and studies were done in 1957 and 1965. These studies helped scientists understand the lava flows.
In 1963, divers from the United States Forest Service collected tree samples from Clear Lake. They found trees preserved under the water. Scientists used radiocarbon dating to find their age. The trees were about 3,200 to 2,700 years old.
Volcanic rock (scoria) has been dug up from Little Nash Crater. It is used for building roads near Santiam Pass. The Carmen Smith Hydroelectric Power Scheme uses the McKenzie River. It generates about 115 horsepower (86 kW) of electricity.
Fun Things to Do
The upper McKenzie River area has many popular places to visit. These include Clear Lake and Tamolitch Pool. At Clear Lake, you can go canoeing, fishing, and boating without motors. There are 34 campsites at Cold Water Cove Campground. There is also a store and restaurant at the Clear Lake Resort.
The volcanic features, like lava flows, in McKenzie Pass are interesting to see. There is also a ski resort at Santiam Pass for winter fun.
