Upcoming Field Trips

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• Citizen science opportunity - basaltic andesite sample collection

  • Start
    1 Sep 2024
  • End
    1 Sep 2025
  • Location
    Various locations

  
  

  Citizen Science Opportunity!

  
  

  Are you interested in participating in a community sampling opportunity by taking a hike and collecting a rock? If so, then read on!

  
  

  The central Oregon Cascades are unusual when compared to the rest of the Cascade volcanic range. This region of the Cascades is dominated by basaltic andesite, a volcanic rock of intermediate composition between basalt and andesite. Basaltic andesite has been the most prevalent type of lava erupted in the central Oregon Cascades for the past ~8 million years. It can be seen in many of the prominent skyline peaks of central Oregon, including North Sister, Black Butte, Mt. Washington, and Three Fingered Jack. Despite the overwhelming dominance of basaltic andesite in this region, the chemical variability of these lavas has not been well documented. Are they related to basaltic lavas that have been erupted in the region? What geologic processes are responsible for generating and sustaining large volumes of basaltic andesite volcanism in this portion of the Cascades?

  Alyssa Smith, PhD candidate at Portland State University, is studying these rocks to improve understanding of their geochemistry and the volcanic history of the central Oregon Cascades. You can watch a recording of her recent COGS presentation here: On Basaltic Andesites: The Dominant Lava Type of the Central Oregon High Cascades Alyssa has been collecting samples from many locations in central Oregon, but more locations remain to be sampled. Knowing that many COGS members enjoy hiking and might be willing to carry a rock hammer, we have worked with to Alyssa to develop this community sampling opportunity.

  
  

  
  

  Alyssa has assembled maps, a spreadsheet with sample locations, and tutorials on collection methods and how to use the Avenza Maps app in the field.These can be accessed in the following FOLDER

  So if you are going to hike Scott Mountain, or Black Crater, or one of the other 77 sites in Alyssa's field area, check out this citizen science opportunity. Contact Alyssa in advance of your hike to get all the details about how to collect samples: aks9@pdx.edu  

  With notice, a Zoom call with Alyssa can also be arranged.

  
  

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• Geo-Exploration: Head of the Metolius & Mile 29 Debris Flow

  • When
    18 Oct 2024
  •  
    8:15 AM - 4:00 PM
  • Location
    Cascade Village Mall - between PetSmart & Ashleys Furniture
  • Spaces left
    2

  Register

  
  

  3-D perspective of bare-earth lidar data looking east towards Green Ridge with the Mile 29 Debris Flow on the left and Lower Bridge on the right click to expand

  
  

  Geo-Exploration: Head of the Metolius & Mile 29 Debris Flow

  Led by Bob Timmer & Bob Jensen

  October 18, 8:15 AM - 4:00 PM

  Registration opens October 11th; limited to 20 participants 

  This field trip will have two components, first a stop at the Head of the Metolius and then a 1-mile hike (2 miles round trip) along the Metolius to examine the Mile 29 Debris Flow. 

  Trip Itinerary

  Meet at Cascade Village Mall between PetSmart & Ashley Furniture @8:15AM to check-in and, optionally carpool. 

  Depart Bend @ 8:30AM from Cascade Village Mall

  Drive west on Highway 20, through Sisters, past Black Butte, and turn right on the Camp Sherman/ Metolius River Road.  Continue north for 2 1/2 miles to a "Y" and proceed right on Forest Service 14. Continue ~2 miles on FS 14 to the Head of the Metolius turn on the left. Proceed to the parking area. Restroom facilities 

  Stop 1 - Head of the Metolius

  We will walk 1/4 mile to the headwaters spring where the Metolius River emerges at the base of Black Butte. James et al. (2000) included the Metolius River headwaters spring in their analysis of groundwater flow in the Deschutes Basin using temperature, stable isotopes, and noble gases. This analysis showed that groundwater discharging at the Metolius headwater spring not only picks up geothermal heat along its flow path, but magmatic volatiles as well. Estimates of the age of the water varies from 47 to 120 years. The headwater spring was known for a relatively constant discharge of 100-125 cfs (Peterson & Groh, 1972). In August 2021, the Bend Bulletin reported, “In June 2018, the head of the Metolius had an outflow of 102 cfs. That dropped to 95.6 cfs in June 2019, 74 cfs in June 2020 and 55 cfs in August 2021”. Flow in September 2023 was reported at 47.9 cfs. Flow in the Metolius increases dramatically with input from springs and tributaries.  

  Return to cars and return to FS 14. Turn left and proceed to north on FS 14 for ~9 miles to the parking area on the east side of the Metolius at Lower Bridge.  

  Stop 2 - Lower Bridge parking area & hike to Mile 29 Debris Flow

  We will hike 3/4 mile downstream from the Lower Bridge Campground to a spot along the river for lunch. We will be hiking along a single-track, lightly maintained trail with small elevation changes. After lunch, we will hike another 1/4 mile on an unmaintained trail to the toe of the Mile 29 Debris Flow.

  Bare-earth lidar data of Mile 29 Debris Flow - click to enlarge
  

  THE MILE 29 DEBRIS FLOW -- WHAT HAPPENED?

  Larry Chitwood and Bob Jensen, Geologists

  Deschutes National Forest

  April 10, 1996

  At the height of the February Flood of 1996, a torrent of water and debris careened 3400 feet down a small canyon on Green Ridge. From the mouth of the canyon, an estimated 600,000 cubic feet (22,000 cubic yards) of debris-laden water shot across a gently-sloped, forested, alluvial fan at about 30 miles per hour. In thirty seconds the torrent reached the Metolius River at Mile 29 leaving in its wake a stark eight-acre field of boulders. About a dozen large trees survived the onslaught. Up to eight vertical feet of bark were battered away by rocks, and mud surged up the trunks leaving stains as high as 25 feet above the ground............

  There is more to the story.......which we will hear from Bob Jensen

  After examination of the toe, we will continue our view of the debris flow by walking cross-country  along the southern margin of the flow to Forest Service road 1499. We will then return to our vehicles with a 1-mile hike along FS 1499 to Lower Bridge.    

  Stop 3 - Down Canyon Viewpoint on FS 1490

  From Lower Bridge, retrace drive on FS 14 about 1/4 mile to FS 1490 on the left. Drive 2 miles up FS 1490 to "down canyon viewpoint". It is nearly impossible to appreciate the gradient of this canyon, and western slope of Green Ridge, until you stand at this viewpoint and look down the canyon. 

  Stop 4 - optional stop panoramic view across the basin

  Depending on time and weather, to drive a further mile up FS 1490 for a panoramic view  

  Return to Bend at 4:00PM

  Notes:

  • Please note that the weather is changing and getting COOLER
  • Please wear appropriate footwear for the hike, appropriate clothing and consider bringing hiking poles 
  • It is hunting season; the risk should be low due to the noise we will likely be making on the trail.
  • Bring a sack lunch and water
  • Please leave your dogs at home
  • Pit toilets are available at Metolius Headwaters and Lower Bridge Campground

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