Ricketts Glen State Park - Geology and Climate

Geology and Climate

Ricketts Glen State Park covers two different physiographic provinces: the Allegheny Plateau in the north, and the Ridge-and-Valley Appalachians in the south. The boundary between these is a steep escarpment known as the Allegheny Front, which rises up to 1,200 feet (370 m) above the land to the south. Within the park, Kitchen Creek has its headwaters on the dissected plateau, then drops approximately 1,000 feet (300 m) down the Allegheny Front in 2.25 miles (3.62 km). Much of this drop occurs in Glen Leigh and Ganoga Glen, two narrow valleys carved by branches of Kitchen Creek, which come together at Waters Meet. Ricketts Glen lies south of and downstream from Waters Meet, and here the terrain becomes less steep. There are 24 named waterfalls in the three glens.

The rocks exposed in the park were formed in the Devonian and Carboniferous periods between 370 and 340 million years ago, when the land was part of the coastline of a shallow sea that covered a great portion of what is now North America. The high mountains to the east of the sea gradually eroded, causing a build-up of sediment made up primarily of clay, sand and gravel. Tremendous pressure caused the formation of the sedimentary rocks that are found in the park and in the Kitchen Creek drainage basin: sandstone, shale, siltstone, and conglomerates.

There are four distinct rock formations within Ricketts Glen State Park. The most recent and highest of these is the late Mississippian Mauch Chunk Formation, composed of "grayish-red shale, siltstone, sandstone, and some conglomerate". This forms the highest points on the Allegheny Plateau and is found north of Lake Jean, forming the land beneath the Red Rocks Job Corps Center and Cherry Ridge to the east. The next formation below this is the Mississippian Pocono Formation, which is buff or gray sandstone with conglomerate and siltstone inclusions. This forms most of the Allegheny Plateau and underlies the park office, Lake Jean and the former Lakes Rose and Leigh. The boulders of the Midway Crevasse, which the Highland Trail passes through, are Pocono Formation sandstone.

The third of the rock formations within the park is the Huntley Mountain Formation, from the late Devonian and early Mississippian. This is made of layers of olive green to gray sandstone and gray to red shale. The Huntley Mountain Formation is relatively hard and erosion resistant. It caps the Allegheny Front and has kept it from eroding as much as the softer Catskill Formation, to the south. The Catskill Formation is the lowest and oldest layer in the park, and is composed of red shale and siltstone up to 370 million years old. The Allegheny Front within the park is named North Mountain and Red Rock Mountain, with the latter name coming from an exposed band of Huntley Formation red shale and sandstone visible along Pennsylvania Route 487 (PA 487).

Geologists and the official Ricketts Glen State Park web page classify the falls at Ricketts Glen State Park into two types. Wedding-cake falls descend in a series of small steps. Within the park, this type of falls usually flows over thin layers of Huntley Mountain Formation sandstone. In bridal-veil falls, the second type, water falls over a ledge and drops vertically into a plunge pool in the stream bed below. Within the park, this type of falls flows over Catskill Formation rocks or the red shale and sandstone of the Huntley Formation. In the park, the harder caprock which forms the ledge from which the bridal-veil falls drops is gray sandstone. The softer red shale below is eroded away by water, sand and gravel to form the plunge pool. Brown's Pennsylvania waterfalls: a guide for hikers and photographers uses four types to classify waterfalls: falls, cascade, slide, and chute.

About 300 to 250 million years ago, the Allegheny Plateau, Allegheny Front, and Appalachian Mountains all formed in the Alleghenian orogeny. This happened long after the sedimentary rocks in the park were deposited, when the part of Gondwana that became Africa collided with what became North America, forming Pangaea. In the years since, up to 5,000 feet (1,500 m) of rock has been eroded away by streams and weather. At least three major glaciations in the past million years have been the final factor in shaping the land that makes up the park today.

The effects of glaciation have made Kitchen Creek within the park "unique compared to all other nearby streams that flow down the Allegheny Front", as it is the only one with an "almost continuous series of waterfalls". Before the last ice age, Kitchen Creek had a much smaller drainage basin; during the ice age, glaciers covered all of the park except the Grand View outcrop. About 20,000 years ago the glaciers retreated to the northeast and glacial lakes formed. Drainage from the melting glacier and lakes cut a sluiceway, or channel, that diverted the headwaters of South Branch Bowman Creek into the Glen Leigh branch of Kitchen Creek. Glacial deposits of debris 20 to 30 feet (6.1 to 9.1 m) thick formed a dam blocking water from Ganoga Lake and what became Lake Jean from draining into Big Run, a tributary of Fishing Creek. The water was instead diverted into the Ganoga Glen branch of Kitchen Creek.

These diversions added about 7 square miles (18 km2) to the Kitchen Creek drainage basin, increasing it by just over 50 percent. The result was increased water flow in Kitchen Creek, which has been cutting the falls in the glens since. The gradient or slope of Kitchen Creek was fairly stable for its flow when it had a much smaller drainage basin, as Phillips Creek to the east still does. Kitchen Creek is now too steep for its present amount of water flow, and over time erosion will decrease the creek's slope and make it less steep. There are rocks with glacial striations visible within the park.

According to the United States Geological Survey Geographic Names Information System, Ricketts Glen State Park is at an elevation of 2,198 feet (670 m). The two highest points in the park are Cherry Ridge, made of Mauch Chunk Formation rock, at 2,461 feet (750 m), and the Grand View outcrop of Huntley Mountain Formation sandstone, at 2,444 feet (745 m). The highest elevation waterfall in the park is Mohawk Falls in Ganoga Glen at 2,165 feet (660 m); the lowest elevation waterfall is Adams Falls, in Ricketts Glen just south of PA 118, at 1,214 feet (370 m).