Contents

Connecting Tunnel

Map of Oregon Caves Showing the Location of the Connecting Tunnel (Source: Oregon Caves Image Library)

The Connecting Tunnel is a human-made passageway, created in 1937 by the Civilian Conservation Corps. The tunnel shape allows for sound reverberation as echoes. It also caused airflow changes throughout the cave.

The Connecting Tunnel is Much Straighter than a Natural Passageway (Source: Oregon Caves Image Library)

Geology

Room Development

Before the Connecting Tunnel there is a small dome in the ceiling where argillite has fallen away. Water flows along the top of the water-resistant and impermeable argillite and then falls through the hole. This is why it drips so much more here (Roth 17).

Since the Connecting Tunnel is human-made, the walls are smoother here than in the rest of the cave. These smooth sides lack fractures so sound bounces off uniformly. Combined with high humidity, which helps transmit sound, this creates echoes.

Reverberation does not occur in the natural areas because the walls are rougher and fractured, which causes sound to reflect in various directions, cancelling out the echoes (Roth 18).The Airlock Door Helped Contain Excess Airflow that was Damaging Cave Formations (Source: Oregon Caves Image Library)

Airflow

The Connecting Tunnel, due to its straightness and size, caused extreme airflow changes within the cave. It allowed colder air to reach further into the cave, causing ice wedging in the Petrified Garden. The installation of the airlock door in 1993 helped to restore the cave airflow to conditions more like those before the tunnel construction (Roth 17; Cigna 229-230).

 

 

 

 

 

References

Cigna, Arrigio. “Climate of Caves.” Encyclopedia of Caves and Karst Science. John Gunn, ed. New York: Fitzroy Dearborn, 2004.

Roth, John. “Interpretive Manual for the Monument’s Showcave”. Cave Junction: Oregon Caves National Monument, 2011.