QUANTIFYING HILLSLOPE ASYMMETRY IN THE VIRGINIA COASTAL PLAIN

Aspect-related hillslope asymmetry is common in a number of landscapes worldwide. Hillslope asymmetry can develop by a combination of diffusive processes, sediment production and flux creating local slope steepness. In this study we determine whether hillslope asymmetry (HA), defined here as the difference in hillslope angle between north-facing and south-facing slopes, occurs on the Mid-Atlantic Coastal Plain in Virginia. The Virginia Coastal Plain is underlain by a sequence of unconsolidated marine, estuarine, and fluvial sediments deposited over the past 5 million years. We conducted remote sensing analysis of slope-aspect at 7 undeveloped forested areas using LiDAR-derived Digital Elevation Models. We quantified HA by comparing the median angles of north and south-facing slopes with angles greater than 5˚. We found that on average, north-facing slopes are 14% steeper than their south-facing counterparts throughout the region. As a mid-latitude location in the northern hemisphere, we predicted HA would correlate with insolation. Insolation-derived HA would attribute the difference in slope angle to solar variation. North-facing slopes receive less direct sunlight, leading to higher soil moisture and increased vegetation cover. These factors cause the rate of soil transportation to be higher on north-facing slopes, while the stability from root systems allowed them to maintain their steeper profile. Previous workers have argued that insolation differences are the primary cause of HA, such that HA increases from south to north in the mid-latitudes. However, on the Virginia Coastal Plain we observe no latitudinal correlation to HA. We will further investigate these findings by adding more sites along both north-south and east-west gradients and also consider the age of the strata at specific sites.