Since the climactic eruption of Mount Mazama, “postcaldera volcanism,” has been conﬁned within the caldera. Most of the volcanic products are hidden from view beneath Crater Lake, but submersible and sonar studies gave scientists an eye beneath the water to the surface of lake floor.
Soon after the caldera formed, eruptions from new vents built the base of Wizard Island and a mound of lava flows near the middle of the caldera called the central platform. As eruptions continued, rain and snowmelt also began to fill the caldera. For the next few hundred years, eruptions from these new vents kept pace above the rising water level. Lava flowed into the deepening lake, creating benches on the flanks of the growing cones that tell scientists how deep the lake was during these eruptions. One set of eruptions from a crater on the west edge of the central platform formed lava tubes or channels that sent lava far out onto the caldera floor.
Eruptions from a vent in the northern part of the caldera, just south of present-day Cleetwood Cove, built Merriam Cone. The erupting Merriam Cone probably never reached the lake surface. The ever-deepening lake eventually submerged the central platform volcano as well. Only Wizard Island managed to grow high enough to stay above the waterline, and only 2% of it is above the lake level today. The last eruptions at Wizard Island took place when the lake was about 80 m (260 feet) lower than today. All of this activity occurred within 750 years after the cataclysmic eruption. The water level continued to rise until reaching near present-day levels, where it encountered a thick layer of porous deposits in the northeast caldera wall. These deposits stabilize lake levels like an overflow drain in a bathtub.
The last known eruption at Crater Lake occurred when a small lava dome erupted underwater on the east flank of the base of Wizard Island about 4,800 years ago. Since that time, the volcano has remained quiet, allowing as much as 30 m (100 ft) of sediment to accumulate on the lake bottom.
The national parks of the United States are often compared to, and indeed inspire, works of art. In fact, the USGS has been regularly contributing new and updated works of art for the national parks—maps.
USGS maps in national parks serve a variety of purposes, from planning to hiking to scientific interest. From outer space or beneath the water’s surface, here are some of the masterpieces of USGS maps in the national parks:
Probably the most famous maps of the national parks are the USGS topographic maps. Topographic maps show the elevation of various features in a landscape, such as the height of hills or the depth of valleys.
The USGS has been producing topographic maps since its founding in 1879. As mapping techniques improved, updated maps have been issued. The USGS recently unveiled a repository for all of its historical topographic maps at USGS TopoView.
Topographic maps have had a great many uses for the national parks. Any large-scale geographic development relies on topographic maps to accurately plan where improvements will go. Famous roads in the national parks, such as Shenandoah’s Skyline Drive or Glacier’s Going-to-the-Sun Road would not have been as successful without accurate topographic maps.
Another important use for these maps is for hikers, who rely on these maps for trail conditions and keeping track of where they are. The national parks have thousands of miles of trails, and USGS topographic maps are a key tool for not getting lost.
National Scenic Trails
As a subset of the topographic maps of national parks, the USGS is hard at work on adding all of the National Scenic Trails to The National Map Products. National scenic trails are those trails that are set aside for their particular national beauty. There are 11 national scenic trails covering parts of at least 32 states.
The most famous is probably the Appalachian National Scenic Trail, which extends some 2,200 miles from Springer Mountain in Georgia to Mount Katahdin in Maine.
The longest of the national scenic trails is the North Country National Scenic Trail, which stretches about 4,600 miles from Crowne Point in New York to Lake Sakakawea State Park in North Dakota.
The USGS started adding the national scenic trails at the start of 2014, and although not all states are covered yet, USGS cartographers are working on getting them added as quickly as possible. Those areas that are covered are best viewed on the US Topo maps and can be downloaded here in GeoPDF form.
Another type of map that the USGS has provided the National Park Service with is geologic maps. These maps show the geologic formations and deposits in a region.
Geologic maps can serve many purposes. The types of rock formations in an area can affect many things, from water availability, ecosystem vulnerability, and even human health. For instance, certain rock formations have high amounts of heavy metals that, if they leach into streams or other water sources, can negatively impact both ecosystem health and human health if people drink the water.
Just like with topographic mapping, geologic mapping has advanced through the years too. Modern remote sensing tools allow for subsurface imaging that was not previously possible. Images like the one below can show both the geologic history of an area and even tectonic faulting, which can produce seismic activity:
USGS maps in the national parks are not limited to ground-level or subterranean areas. They can also be conducted remotely, via tools like airborne lidar or satellite imagery.
Lidar, which stands for light detection and ranging, is a tool normally used for elevation information, such as in the topographic maps mentioned previously. However, USGS research has also allowed it to be used to map vegetation density in sensitive ecosystems.
Mapping vegetation density is important to park managers, because it is one measure of ecosystem health. In the Barataria Preserve of Jean Lafitte National Historical Park of Louisiana, the delicate coastal marshes are threatened by coastal erosion. Accurate mapping of the vegetation density allows park managers to keep tabs on the health of the marsh.
Remote sensing maps of national parks can even be conducted from satellites. The Landsat satellite, operated by the USGS and NASA, regularly provides maps of the national parks as it orbits overhead. These maps can provide critical services to park managers, especially during forest fires.
Landsat maps can not only help fire fighters track the fire as it spreads across the national parks, but also aid scientists’ understanding of how the land recovers.
Start with Science
As the National Park Service celebrates 100 years of managing the Nation’s Crown Jewels, the USGS will continue to provide the best maps forward for the next 100 years and beyond.