Geography of Lake Lahontan

Lake Lahontan Shoreline Processes

The most notable part of the Lake Lahontan basin is the ancient shoreline formations. Lake Lahontan’s immense size allowed it to produce shoreline formations that rival the magnitude of coastal-marine formations which are found only in a select few places around the world, almost always formed by large pluvial paleolakes.

Wave Cut Terraces

Wave-cut terraces are definitely the best-known formation of the Lake Lahontan basin. These terraces are formed through an erosional-depositional process that occurs in two main stages. The first stage is the formation of what is known as a terrace tread. A terrace tread is the horizontal component of a wave-cut terrace. The terrace tread is formed during a long period of consistent water levels in which waves Terrace.gif (15705 bytes) continually erode and deposit material to form a gently-sloping horizontal surface. This process continues until the lake undergoes a uniform drop in lake level. The second stage of terrace formation occurs during and after this drop in water level. While the water level is dropping, the waves begin to erode a portion of the terrace tread, which over time begins to create a nearly vertical wall, called a terrace riser. The terrace riser is completely formed once the lake level has stopped subsiding, in which case another terrace tread begins to form, and the process is started over again. The end result is a series of terrace treads and risers that show the slow declination of the water level.

View a photo of a wave-cut terrace near Pyrimid Lake, Nevada

A model of the two main terrace-forming stages broken into six parts:

a) Waves erode a gently sloping surface called a terrace tread
b) Lake levels decline leaving the terrace tread mostly horizontal
c) Waves begin to form a terrace riser by eroding the lower parts of the terrace tread
d) As the water level drops at a relatively uniform rate, the terrace riser becomes more defined

e) The terrace riser is finished being formed and a separate terrace tread is formed in the process

f) The lake level recedes below the wave-cut terrace

Barrier Spits

Spits are depositional formations caused by the lateral movement of water along a shoreline known as littoral drift. Waves energy rarely, if ever, makes perfectly perpendicular contact with the shoreline. Instead, the waves hit the shoreline at an angle, causing a lateral movement of water and sediment in whichever direction the waves are angled toward. This lateral movement results in the deposition of sediment along the coastline where wave energy goes from high to low. For the most part, spits are thought of as coastal marine formations, but they are also very evident in many large lakes that exist today.

SpitArtb.gif (17453 bytes)

(Above) Barrier spits from due to wave action known as littoral drift which deposits sediments at a low energy area.