Many of the earth science/physical geography professors and grad students I've talked to are almost unanimous in enjoying the field work aspect of their research. However, some of them are apprehensive about GIS technology, believing that increased ubiquity of the software will reduce or even eliminate the need for hard data gathering that is a big part of field work. Is that true? I don't know. I can surmise that depending on circumstances it could be, and I've certainly been to a few geomatics presentations where the crux of a new technique is to gather empirical geographic data without leaving the desk.
DEM) files is akin to a needle-in-haystack search. So I was surprised when looking up information on Crater Lake and stumbling across USGS's collection of DEM files on the lake's bathymetry. Scratch that ... I wasn't surprised, as I've gotten used to the ridiculous restrictions my own government places on what should be freely available public information (these restrictions aren't limited to the geographic realm). One of my GIS bosses remarked on how his students are finding it really hard to collect digital data for their term projects, and he further mentioned that most projects involve analysis of geographic phenomena in BC. Even my own work projects involving examinations of local watersheds was shelved due to lack of shapefiles or anything that could be converted to such without a lifetime of eye damage.
But is the USGS stuff I found really any good? Cracking open ArcGIS to take a look at the bathymetry data, I was immediately struck with déjà vu. Where had I seen this layout of Crater Lake before? Of course, I see a variation of it in passing everyday, pinned up on my apartment wall:
|At a gift shop in Crater Lake park, there was a huge 6-foot tall version of the above geologic map with even more detail. Alas, it was only for display, but the 4-foot tall version available for customers has good detail for a pretty penny.|
|The virgin view of Crater Lake in ArcGlobe [Top Left]. USGS 7.5 arcminute DEM of Crater Lake, showing shaded relief bathymetry [Top Right]. Angled perspective of 7.5 arcminute Crater Lake DEM, with annotated structures [Bottom]|
On the subaqueous features/structures of Crater Lake
Rhyodacite Dome = youngest (5 Ka), shallowest subaqueous feature. It is a highly silicic lava dome that has formed from a vent that intruded through both the andesitic Central Platform & the eastern flank of Wizard Island. Rhyodacitic flows and domes were common in Mazama's history between 40-5 Ka.
Central Platform = Subaerial andesite flows that experienced magma differentiation from within the primary chamber. Successive eruptions (7-6 Ka) that built up the platform were above lake level, giving the platform a low, broad relief until flows met the old shoreline.
Merriam Cone = Cinder cone whose lower portion/foundation was formed as a resurgent dome, composed of subaqueous andesite, formed from completely submarine eruptions circa 7.7-7.5 Ka. It has a nearly geometrically idealized cone shape. Peak is ~150m below current lake level. Origins and formation still not agreed upon (Resurgent dome or Cinder cone or how much of a combination??).
Phantom Ship = Oldest (400 Ka), partially subaqueous feature. Considered to be the top of a basic-andesitic volcanic dike, a remnant of a small vent that might have fed parasitic cones on pre-cataclysmic Mazama's eastern flank (see also Devil's Backbone).
Various Depositional Basins = Colluvium, volcaniclastics, volcanic breccia, and ash particles, all weathered and transported to the low-lying depressions of the caldera. The rim has plenty of talus slopes. There is a huge landslide deposit on the southern end of the lake, called the Chaski Bay landslide, with a debris avalanche volume of 0.1 km3 (couldn't find an exact date on the slide). Evidence of the slide triggering a mild tsunami is found at Cleetwood Cove on the northern end.
- Oregon Explorer - Crater Lake Data Clearinghouse
- USGS - Mount Mazama and Crater Lake: Growth and Destruction of a Cascade Volcano
- USGS - Seafloor Mapping: Crater Lake shaded relief
- USGS - Merriam Cone Perspective View
- Charles Bacon et al. - Late Pleistocene granodiorite source for recycled zircon and phenocrysts in rhyodacite lava at Crater Lake, Oregon