Field trip to Rocky Mountain National Park CSU/POLENET/SERCE Glacial Seismology School June 2017 Compiled by Daniel McGrath

Overview: We’ll depart from CSU around 12 pm, head south to Loveland, and then turn west and head up the Big Thompson Canyon before arriving in Estes Park. We’ll pass through Estes Park quickly (we hope…there can be lots of tourist traffic) and enter RMNP via the Fall River Entrance.

We’ll have ~6 major stops along the way, before returning to Estes Park around 6 pm for dinner at Ed’s Cantina. We’ll return to CSU/Fort Collins ~9-9:30 pm.

1 Brief history of Rocky Mountain National Park: Humans have had a presence in the area that is now Rocky Mountain National Park for thousands of years. There is evidence of human activity in the park area from as early as 10,000 years ago, when Native Americans began to hunt and explore the fertile land. In 1803, the United States government acquired the Louisiana Purchase, which included most of the land that is now Rocky Mountain National Park. The first visitors after the acquisition included mostly fur trappers and explorers. As the 19th century progressed, miners, homesteaders, ranchers, and hunters began to inhabit the area as well. In 1909, a naturalist, guide, and local lodge owner named began several years of traveling the nation to lecture, lobby, and advocate for the creation of a new national park. Mills’ efforts came to fruition on January 26, 1915 when President Woodrow Wilson signed the Rocky Mountain National Park Act into law. Rocky Mountain National Park became the 10th national park in the United States. As visitation increased to the park after World War I, park superintendents and rangers began building comfort stations, museums, and trails to better accommodate visitors. With the Great Depression of the 1930s came the Civilian Conservation Corps, whose efforts included the planting of trees, management of wildlife, and construction of more roads, trails, and buildings. It was also during the 1930s that the construction of was completed, with the road opening in 1932. Trail Ridge Road connected east and west entrances to the park for vehicular visitors, and also provided a spectacular drive that showcases the park: through forests, across meadows, and over the open tundra of the high country. During World War II, park visitation decreased dramatically. After the war, the Baby Boomer generation brought a surging increase of visits to the park. It was around this time that new kinds of facilities, called visitor centers, were built. At these visitor centers guests could talk to rangers, watch movies and attend seminars, and gain other info about the park. Visitation continued to grow throughout the 1960s and 1970s, and the park grew as well. Assigned backcountry campsites, shuttle buses, and additional roads, trails, and facilities were added. The park adopted a more conservation-oriented approach to managing everything from wildlife to wildfires as well. Today, the park is still a popular tourist destination, with over 3 million visitors per year. The town of Grand Lake continues to serve visitors as well, proudly offering lodging, dining, recreation, and other services to park tourists.

Source: http://grandlakechamber.com/rocky-mountain-national-park-history/

2 Stop 1: Erosion from 2013 floods

Starting on September 9, 2013, a slow-moving cold front stalled over , clashing with warm humid monsoonal air from the south. This resulted in heavy rain and catastrophic flooding along Colorado's from Colorado Springs north to Fort Collins. The situation intensified on September 11 and 12. Boulder County was worst hit, with 9.08 inches (231 mm) recorded September 12 and up to 17 inches (430 mm) of rain recorded by September 15, which is comparable to Boulder County's average annual precipitation (20.7 inches, 525 mm). This caused the rivers to swell (after already experiencing higher flows due to late summer precipitation in the mountains). Higher flows headed toward the lower elevation cities, which were also receiving much above average precipitation. All of this combined to greatly increase the rivers' flows through the cities. In the hydrographs to the left, the yellow triangles denote the median (normal) flow during September at their respective locations. Normal flows for Boulder Creek, , and Poudre River are all around 10 to 50 cfs (cubic feet per second). On September 9, those gages showed flows close to normal. On September 12, flows greatly increased to over 6000 cfs on Boulder Creek, 5000 cfs on the Big Thompson, and 9000 cfs on the Poudre River. That's over 10,000% of average! Source: Wikipedia, http://coflood2013.colostate.edu/runoff.html. This was the second very large flood to occur in this steep canyon in the past 50 years. A July 31, 1976 a thunderstorm dropped ~12 inches of rain in a four-hour period, generating a flood that was the deadliest in Colorado history, taking 144 lives.

3 Stop 2: Pinedale lateral/terminal

We’ll stop where US 34 crosses over a large formed during the Pinedale glaciation (maximum around 23,500 and 21,000 years ago). Only the last two glaciations are well documented in North America. The most recent glaciation (the Wisconsin) saw continental ice sheets reach as far south as Wisconsin and Seattle. In the this glaciation is called the Pinedale glaciation, named after the town next to the Mountains of Wyoming where evidence for it was first documented. No large ice sheets existed in the Rocky Mountains, but several small ice sheets (ice caps) and large valley glaciers existed in many ranges and an ice sheet covered the peaks of the Wind River Range. In the Front Range valley glaciers were up to 45 km long, and a small ice sheet formed at the headwaters of the outside of Fort Collins. Source: http://www.glaciers.pdx.edu/Projects/LearnAboutGlaciers/ROMO/GlcBasics.html Glaciation in the park probably started about 1.6 million years ago. Specific evidence of the earliest glaciations doesn't exist because moraines formed by the early glaciers were destroyed by glaciers that followed later. Each time glaciers flowed down the mountain valleys they eroded the valley sides and bottoms, helping to straighten and deepen them, removing evidence of earlier glaciations. Evidence of the last two major periods of ice accumulation is quite clear, however. The first of these two glacial periods is called the Bull Lake Glaciation. The Bull Lake advance began about 300,000 years ago and ended about 130,000 years ago. A few isolated remnants of moraines from the Bull Lake glaciers can be identified at various places in the park. They indicate that the amount of ice in the valleys then was equal to or greater than ice volume during the most recent period of glaciation. After the Bull Lake glaciation came a warmer period that lasted about 100,000 years. The last major glacial episode, called the Pinedale Glaciation, began about 30,000 years ago when Earth's climate once again cooled. The Pinedale glaciers reached their maximum extent between 23,500 and 21,000 years ago. Most of the major valleys in the park were filled with glaciers during this time. One of the largest of the park glaciers, with a length of 13 miles (21 km), was in Forest Canyon just south of the high point of today's Trail Ridge Road. The largest glacier, about 20 miles (52 km) long, was the ice flow that occupied the Colorado River Valley on the west side of the park. The ice in many of these glaciers reached thicknesses of 1,000 to 1,500 feet (305 to 457 m). Source: https://www.nature.nps.gov/geology/parks/romo/

4

Note stark transition between fluvial V-shaped valley and glacial U-shaped valley as we enter RMNP through Fall River entrance (grey/green shading boundary on map)

Stop #3: /Sheep Lakes:

http://www.rmnp.com/RMNP-Areas-TrailRidge-RainbowCurve.HTML

Horseshoe Park is named for the glacial moraines that rim the valley in the shape of a horseshoe. During a warming trend as a glacier recedes, a stream laden with sediment is “washed out” from the glacier (hence the term “outwash”) and deposited in a flat area below. Depressions, known as kettles, often pockmark outwash and moraines. Kettles form when a block of stagnant ice becomes wholly or partially buried in sediment and ultimately melts, leaving a pit behind. Kettles can be feet or miles long but are usually shallow. In many cases, water eventually fills the depression and forms a pond or lake, called a kettle pond or kettle lake. Sheep Lakes are kettle ponds that lie in the outwash on the floor of Horseshoe Park. These small ponds are intermittent and usually dry up late in the summer. visit these kettle ponds, primarily during their lambing season in May and June, to drink the water and eat the mud, which is rich in nutrients for lactating ewes. We have the glaciers to thank for this prime wildlife- viewing area.

5 Stop #4: Lawn Lake Flood alluvial fan

Source: https://www.e-education.psu.edu/geosc10/l4_p4.html

At approximately 0530 MDT on the morning of July 15, 1982, failed. The dam was a 79- year- old (Pitlick, 1993b), 26- foot (7.9- m) high earthen dam (Jarrett and Costa, 1986) near the head of the valley. The dam released 674 acre- feet (831,716 m3) of water and an estimated peak discharge of 18,000 cfs (Jarrett and Costa, 1986). By comparison, investigators estimate the “500 year flood” in this area to have peak discharges of only about 400 cfs (Hoyt, 1987). Thus the hydrologic consequences of the Lawn Lake dam failure were truly exceptional, and peak discharges of the flood far exceeded naturally occurring flows (Pitlick, 1993a). Source: https://www.nature.nps.gov/geology/parks/romo/romo_gre_rpt_view_low.pdf

Stop (really a drive) #5: Trail Ridge Road to Alpine Visitors Center and Many Parks Curve (and potentially other stops)

6

Snow in 2011.

Source: http://denver.cbslocal.com/2011/05/26/trail-ridge-road-memorial-day-weekend/

Stop #6: Moraine Park

We’ll finish by exploring Moraine Park to take a closer look at the large moraines formed during the Bull Lake and Pinedale glaciations.

Moraine Park's long, wooded slope at its south edge is a classic example of a lateral moraine, rock rubble that forms at the side of a glacier. Close examination of the

7 moraines along both north and south flanks of Moraine Park show deposits of the older Bull Lake Glaciation and the younger, more prominent Pinedale Glaciation.

Modern “glaciers” in RMNP (possible stop along Road depending on time)

Braddock and Cole (1990) identified 34 persistent snow banks and ice masses in the vicinity of Rocky Mountain National Park. These include the snow and ice bodies shown on 1:24,000- scale topographic maps published between 1957 and 1962. Fourteen of the ice masses have been named: Rowe Glacier (between Rowe Peak and Hagues Peak), Sprague Glacier (at Irene Lake in Spruce Canyon), Tyndall Glacier (at the head of Tyndall Creek), (east of Andrews Pass), Taylor Glacier (at the head of Icy Brook), Chiefs Head Peak Glacier (above Frozen Lake), Mills Glacier (on the east side of ), Moomaw Glacier (south of The Cleaver), and the six St. Vrain Glaciers (outside of the park at the head of Middle St. Vrain Creek).

All but one of these snow banks or ice masses are on the east side of the Continental Divide; the exception is the mass above Murphy Lake (near Snowdrift Peak). All but one occur at the heads of cirques: north-, northeast-, or east-facing; the exception is the large snowbank northeast of Rowe Mountain, which is in a northeast-facing gully. Some of the ice masses, such as Andrews Glacier, are actively moving and can be considered actual glaciers; others are stagnant. Winter winds—sometimes at velocities that exceed 200 miles (320 km) per hour— blow snow towards the east over the Continental Divide where it drifts into the Pleistocene- age cirques and nourishes some small glaciers. This process of snow deposition gives these “wind-drift glaciers” their name. Source: https://www.nature.nps.gov/geology/parks/romo/romo_gre_rpt_view_low.pdf

These glaciers retreated through the first half of the twentieth century, and then slightly expanded from the mid 1940s through the end of the century (Hoffman et al., 2007).

8 However, these glaciers are very small, so interannual changes in area can be large (i.e., 2011 was a very big snow year on the Front Range).

Source: Hoffman et al., 2007; updated by McGrath et al., in prep.

Using historical topographic maps and a suite of new geodetic observations (DEMs derived from terrestrial LiDAR and commercial satellite stereo image pairs), McGrath et al. (in prep) are examining the long-term geodetic balances of the glaciers along the Front Range.

9

Ground penetrating radar surveys in 2016 and 2017 revealed the importance of wind redistribution to the health of these glaciers, with ~10x more snow being deposited on the glaciers than just ~1 km down valley. Each winter, a large “dune” forms along the central axis of the glacier. This excess in accumulation helps Andrews and the other glaciers along the Front Range to survive despite very high ablation rates.

At its thickest point, Andrews Glacier exceeds 70 m, although much of the glacier is between 5-25 m in thickness.

10