# grdseamount¶

Create synthetic seamounts (Gaussian, parabolic, polynomial, cone or disc; circular or elliptical)

## Synopsis¶

**gmt grdseamount** [ *table* ]
**-G***outgrid*
**-I***increment*
**-R***region*
[ **-A**[*out*/*in*][**+s***scale*] ]
[ **-C**[**c**|**d**|**g**|**o**|**p**] ]
[ **-D***unit* ]
[ **-E** ]
[ **-F**[*flattening*] ]
[ **-H***H*/*rho_l*/*rho_h*[**+d***densify*][**+p***power*] ]
[ **-K**[*densitymodel*] ]
[ **-L**[*hn*] ]
[ **-M**[*list*] ]
[ **-N***norm* ]
[ **-Q***bmode*[/*fmode*][**+d**] ]
[ **-S**[**+a**[*az1*/*az2*]][**+b**[*beta*]][**+d**[*hc*]][**+h**[*h1*/*h2*]][**+p**[*power*]][**+t**[*t0*/*t1*]][**+u**[*u0*]][**+v**[*phi*]] ]
[ **-T***t0*[/*t1*/*dt*][**+l**] ]
[ **-Z***level* ]
[ **-V**[*level*] ]
[ **-W***avedensity* ]
[ **-bi**binary ]
[ **-e**regexp ]
[ **-f**flags ]
[ **-i**flags ]
[ **-r**reg ]
[ **--PAR**=*value* ]

**Note:** No space is allowed between the option flag and the associated arguments.

## Description¶

**grdseamount** will compute the combined topographic shape of multiple synthetic seamounts given
their individual shape parameters. We read from *table* (or standard input) a list of seamount
locations and sizes and can evaluate either Gaussian, parabolic, conical, polynomial or disc
shapes, which may be circular or elliptical, and optionally truncated. Various options are available
to modify the result, including an option to add in a background depth or set unmodified nodes to NaN
(more complicated backgrounds may be added separately via grdmath). The input data
must contain *lon*, *lat*, *radius*, *height* for each seamount. For elliptical features (requires
**-E**), we expect *lon*, *lat*, *azimuth*, *semi-major*, *semi-minor*, *height* instead. If
flat seamount tops is specified (via **-F**) with no value appended, then an extra column with
*flattening* is expected (**-F** cannot be used for plateaus). For temporal evolution of topography
the **-T** option may be used, in which case the data file must have two additional columns with
the start and stop time of seamount construction. In this case, you may choose to write out a
cumulative shape or just the increments produced for each time step (see **-Q**). If land slides
are considered (**-S**), then this initial set of input columns are followed by one or more groups
of slide parameters; see **-S** for the arrangement. Finally, for mixing different seamount shapes
in the input *table* you can use the trailing text to give the shape code by using **-C** without
appending an argument.

## Required Arguments (if **-L** is not given)¶

*table*One or more ASCII (or binary, see

**-bi**[*ncols*][*type*]) data table file(s) holding a number of data columns. If no tables are given then we read from standard input.

**-G***outgrid*[=*ID*][**+d***divisor*][**+n***invalid*][**+o***offset*|**a**][**+s***scale*|**a**][:*driver*[*dataType*][**+c***options*]]

Give the name of the output grid file. If

-Tis set thenoutgridmust be a filename template (See File Template for details). Optionally, append =IDfor writing a specific file format (See full description). The following modifiers are supported:

+d- Divide data values by givendivisor[Default is 1].

+n- Replace data values matchinginvalidwith a NaN.

+o- Offset data values by the givenoffset, or appendafor automatic range offset to preserve precision for integer grids [Default is 0].

+s- Scale data values by the givenscale, or appendafor automatic scaling to preserve precision for integer grids [Default is 1].

Note: Any offset is added before any scaling.+saalso sets+oa(unless overridden). To write specific formats via GDAL, use =gdand supplydriver(and optionallydataType) and/or one or more concatenated GDAL-cooptions using+c. See the “Writing grids and images” cookbook section for more details.

**-I***x_inc*[**+e**|**n**][/*y_inc*[**+e**|**n**]]Set the grid spacing as

*x_inc*[and optionally*y_inc*].**Geographical (degrees) coordinates**: Optionally, append an increment unit. Choose among:**m**to indicate arc minutes**s**to indicate arc seconds**e**(meter),**f**(foot),**k**(km),**M**(mile),**n**(nautical mile) or**u**(US survey foot), in which case the increment will be converted to the equivalent degrees longitude at the middle latitude of the region (the conversion depends on PROJ_ELLIPSOID). If*y_inc*is given but set to 0 it will be reset equal to*x_inc*; otherwise it will be converted to degrees latitude.

**All coordinates**: The following modifiers are supported:**+e**to slightly adjust the max*x*(*east*) or*y*(*north*) to fit exactly the given increment if needed [Default is to slightly adjust the increment to fit the given domain].**+n**to define the*number of nodes*rather than the increment, in which case the increment is recalculated from the number of nodes, the*registration*(see GMT File Formats), and the domain.**Note**: If**-R***grdfile*is used then the grid spacing and the registration have already been initialized; use**-I**and**-R**to override these values.

**-R***xmin*/*xmax*/*ymin*/*ymax*[**+r**][**+u***unit*]Specify the region of interest. (See full description) (See cookbook information).

## Optional Arguments¶

**-A**[*out/in*][**+s***scale*]Build a mask grid only that may be used to manipulate gridded data sets to exclude or to isolate seamount observations; append outside/inside values [1/NaN]. Here, height and flattening are ignored and

**-L**,**-N**and**-Z**are disallowed. Optionally, use**+s**to increase all seamount radii or semi-axes first (e.g., “bleeding the mask outwards”) [1].

**-C**[**c**|**d**|**g**|**o**|**p**]Select a seamount shape function: choose among

**c**(cone),**d**(disc),**g**(Gaussian)**o**(polynomial) and**p**(parabola) [Default is Gaussian]. All but the disc can furthermore be truncated via a flattening parameter*f*set by**-F**. If**-C**is not given any argument, then we will read the shape code from the input file’s trailing text. If**-C**is not given at all, then we default to Gaussian seamounts [**g**].**Note**: The polynomial model has a normalized amplitude*v*for a normalized radius \(u = r / r_0\) that is given by \(v(u) = (1+u)^3(1-u)^3/(1+u^3)\). It is comparable to the Gaussian model (its volume is just ~2.4% larger), and*v*goes exactly to zero at the basal radius \(r_0\).

**-D***unit*Append the Cartesian unit used for horizontal distances in the input file (see Units). Not allowed for geographic data, which we automatically convert to km using a flat Earth assumption.

**-E**Set elliptical data file format. We expect input records to contain

*lon, lat, azimuth, semi-major, semi-minor, height*(with the latter in meter) for each seamount [Default is Circular data format, expecting*lon, lat, radius, height*]. To mix circular and elliptical seamounts you must use**-E**and provide the circular parameters as elliptical ones via*azimuth = 0*and*semi-major = semi-minor = radius*.

**-F**[*flattening*]Seamounts will be truncated to guyots. Append

*flattening*from 0 (no flattening) up to, but not including, 1. If no argument is given then we expect to find the flattening in the last input column [no truncation]. Ignored if used with**-Cd**.

**-H***H*/*rho_l*/*rho_h*[**+d***densify*][**+p***power*]Set reference seamount parameters for an

*ad-hoc*variable radial density function with depth. Give the low and high seamount densities in \(\mbox{kg/m}^3\) or \(\mbox{g/cm}^3\) and the fixed reference height*H*in meters. Use modifiers**+d**and**+p**to change the water-pressure-driven flank density increase over the full reference height [0] and set the variable density profile exponent*power*[1, i.e., a linear change]. Below,*h(r)*is the final height of any seamount and*z(r)*is a point inside the seamount. If the seamount is truncated (via**-F**) then*h(r)*refers to the original height.**Note**: If**-V**is used then we report the mean density for each seamount processed. The radial density function is thus defined (with \(\Delta \rho_s = \rho_h - \rho_l\) and the*densify*setting is \(\Delta \rho_f\)):

**-K***densitymodel*Append the file name for a crossection grid with the predicted densities of the reference model. We use normalized coordinates (both

*x*(radius) and*y*(height) go from 0 to 1 in increments of 0.005), yielding a fixed 201 x 201 grid.**Note**: This option can be used without creating the seamount grid, hence**-R**,**-I**,**-G**, and**-D**are not required.

**-L**[*hn*]List

*area*,*volume*, and*mean height*for each seamount; no grid will be created. Optionally, append*hn*for a noise-floor cutoff level below which we ignore area and volume [0].

**-M**[*list*]Write the times and names of all relief grids (and density grids if

**-W**is set) that were created to the text file*list*. Requires**-T**. If no*list*file is given then we write to standard output. The leading single numerical column will be time in years, while the last trailing text word is formatted time. The output listing is suitable as input to grdflexure.**Note**: The output records thus contain*time reliefgrid*[*densitygrid*]*timetag*.

**-N***norm*Normalize the relief grid(s) so the maximum grid height equals

*norm*[no normalization].

**-Q***bmode*[/*fmode*][**+d**]Set build modes. Can only be used in conjunction with

**-T**. The default is**-Qc**/**g**; append alternative mode settings (separated by a slash if both are specified) to change that:The required

*bmode*determines how we construct the surface: Specify**c**for cumulative volume through time or**i**for the incremental volume added for each time increment.The optional

*fmode*determines the volume flux curve we use: Give**c**for a constant volume flux or**g**for a Gaussian volume flux [Default] between the start and stop times of each feature.

These flux models integrate to a linear and error-function volume fraction curve over time, respectively, as shown below. By default, we compute the exact cumulative and incremental values for the seamounts specified. Append

**+d**to instead approximate each incremental layer by a disc of constant thickness.

**-S**[**+a**[*az1*/*az2*]][**+b**[*beta*]][**+d**[*hc*]][**+h**[*h1*/*h2*]][**+p**[*power*]][**+t**[*t0*/*t1*]][**+u**[*u0*]][**+v**[*phi*]]

Set parameters controlling the simulation of sectoral, rotational land slides by providing suitable modifiers. Parameters given on the command line apply to all seamounts equally. However, if a modifier is set but not given an argument then we read those arguments from the end of the input record; the order of such input arguments follows alphabetically from the modifier codes (and not the order the modifiers may appear on the command line). Repeat the slide group columns if there is more than one slide to read per seamount. Use these modifiers to set relevant slide parameters:

+aspecifies the azimuthal sector affected by the slide [0/360].

+bsets a positive power coefficient \(\beta\) for the normalized slide volume fraction time-curve \(\psi(\tau) = \tau^\beta\) [Default is linear, i.e., 1]. See+tfor definition of \(\tau\).

+dsets the flank level of the seamount where the debris deposit begins [\(h_1/2\)].

+hsets the lower and upper heights of the flank source area generating the landslide.

+pactivates angular variation in the radial slide profile; append a power parameterpower > 2.Note: For multiple slides it is valid to providepower= 0 for some (either via command argument or read from file), which simply turns off angular variation for those slides. See+ufor the radial slide profile setting.

+tsets the time span over which the slide develops via \(\psi(\tau)\) (see+b), where \(\tau = (t - t_0)/(t_1 - t_0)\) is the normalized time span 0-1 when the slide occurs; this modifier also requires-Tto be set.

+usets normalized radial slide shape parameter \(u_0 > 0\) [0.2].

+vsets desired fractional volume \(\phi\) of the slide (in percent) relative to the entire seamount volume.

Note: If+vis set then we must compute the correspondingu0, hence+uis not allowed. If+b,+d, or+uare not set then their defaults are used for all slides. Currently, we support a maximum of 10 slides per seamount.

**-T***t0*[/*t1*/*dt*][**+l**]Specify

*t0*,*t1*, and time increment (*dt*) for a sequence of calculations [Default is one step, with no time dependency]. For a single specific time, just give start time*t0*. Default*unit*is years; append**k**for kyr and**M**for Myr. For a logarithmic time scale, append**+l**and given the number of steps*n*instead of increment*dt*. Alternatively, give a file with the desired times in the first column (these times may have individual units appended, otherwise we assume year). If**-T**is set, then the input seamount table is expected to have to extra columns for the*start*and*stop*time following the initial seamount parameters (but before any slide groups; see**-S**). Because positive time is in years before present, we require*t0*>=*t1*time.**Note**: A grid will be written for all time-steps even if there are no relief or changes for one or more output times.

**-V**[*level*]Select verbosity level [

**w**]. (See full description) (See cookbook information).

**-W***avedensity*Give the name of the vertically averaged density grid file. If

**-T**is set then*avedensity*must be a filename template (See File Template for details). Requires**-H**to define the density model.

**-Z***level*Set the background water depth [0]. As all seamounts have positive relief, you may use a larger negative

*level*to place them under water. Alternatively, append NaN if you wish to flag unused nodes (not allowed if**-Qi**is used).

**-bi***record*[**+b**|**l**] (more …)Select native binary format for primary table input. [Default is 4 input columns].

**-e**[**~**]*“pattern”*|**-e**[**~**]/*regexp*/[**i**] (more …)Only accept data records that match the given pattern.

**-f**flagsGeographic grids (dimensions of longitude, latitude) will be converted to km via a “Flat Earth” approximation using the current ellipsoid parameters.

**-h**[**i**|**o**][*n*][**+c**][**+d**][**+m***segheader*][**+r***remark*][**+t***title*] (more …)Skip or produce header record(s). Not used with binary data.

**-i***cols*[**+l**][**+d***divisor*][**+s***scale*|**d**|**k**][**+o***offset*][,*…*][,**t**[*word*]] (more …)Select input columns and transformations (0 is first column,

**t**is trailing text, append*word*to read one word only).

**-r**[**g**|**p**] (more …)Set node registration [gridline].

**-:**[**i**|**o**] (more …)Swap 1st and 2nd column on input and/or output.

**-^**or just**-**Print a short message about the syntax of the command, then exit (

**Note**: on Windows just use**-**).**-+**or just**+**Print an extensive usage (help) message, including the explanation of any module-specific option (but not the GMT common options), then exit.

**-?**or no argumentsPrint a complete usage (help) message, including the explanation of all options, then exit.

**--PAR**=*value*Temporarily override a GMT default setting; repeatable. See gmt.conf for parameters.

## Units¶

For map distance unit, append *unit* **d** for arc degree, **m** for arc
minute, and **s** for arc second, or **e** for meter [Default unless stated otherwise], **f**
for foot, **k** for km, **M** for statute mile, **n** for nautical mile,
and **u** for US survey foot. By default we compute such distances using
a spherical approximation with great circles (**-jg**) using the authalic radius
(see PROJ_MEAN_RADIUS). You can use **-jf** to perform
“Flat Earth” calculations (quicker but less accurate) or **-je** to perform
exact geodesic calculations (slower but more accurate; see
PROJ_GEODESIC for method used).

## File Template¶

The format statements allowed in grid file templates require you to follow these rules:

To use the formatted time-tag as part of the file name you must use just a single %s format as part of the template (e.g., smt_%s.grd).

If you want to control the numerical formatting of the names but still have the common time unit appended then you must compose a template that has a floating point format before a later %c format for the unit. For example, smt_%05.1f%c.grd will create names like smt_001.1M.grd names. The times will be scaled to match the unit.

If you do not want any units then simply give a template with just one floating point format, e.g., smt_%05.1f_name.grd. The times will be used as is (i.e, unscaled).

For details on the format statements, see printf C language format syntax.

## Slide simulation specifics¶

The simulation of land slides via **-S** is not a physical model (apart from preserving mass). Instead,
we approximate the shapes of rotational landslides and their evolution via simple geometric shapes and functions.
The radial slide height is modeled as

where \(u = (r - r_2)/(r_1 - r_2)\) is the normalized horizontal distance of the rupture
surface. This shape can be modulated by using **+u** to change \(u_0\).

By default, the radial slide profile is fixed regardless of where in the slide sector we look. However, gentle or more abrupt angular variation can be added to \(h_s(r)\) via the function

where \(\gamma = 2 (\alpha - \alpha_1)/(\alpha_2 - \alpha_1) - 1\) and *p* is the power exponent
that can be set via **+p**. When enabled, we use \(s(\alpha)\) to scale the radial slide profile
so that it starts of at zero at the two sectoral locations and then grows more (larger *p*) or less
(smaller *p*) rapidly as we enter the slide sector. This modifier has the effect of smoothing the step
functions we otherwise encounter as we enter the slide sector.

Finally, an observed landslide may not have occurred instantly but developed over a finite time period. We can simulate that by distributing the total slide volume over this time. The normalized volume rate distribution is simulated by

where \(\tau\) is the normalized time during a slide event. We use this function to compute the portion
of the slide volume that should be deposited at a given time *t*. Modifier **+b** is used to specify the
power exponent \(\beta\) [1].

## Notes¶

Because the Gaussian curve only drops to 1.11% of its peak amplitude at the base radius (3 sigma) of a seamount, we actually evaluate Gaussian curves all the way to 4 sigma so that the amplitude drops to 0.034% of peak height before we jump to zero. This prevents the otherwise very noticeable step at the base of the seamount.

## Examples¶

To compute the shape of a circular Gaussian seamount located at 1W, 2S on a 1 arc minute grid for a basal radius of 30 km and a height of 4500 meters, try:

```
echo 1W 2S 30 4500 | gmt grdseamount -R1:30W/0:30W/2:30S/1:30S -I1m -Ggeo_circ_smt.nc
gmt grdimage geo_circ_smt.nc -B -png circ
```

To compute the shape of an elliptical conic seamount located at 200,400 on a 1x1 Cartesian grid for basal semi-major axis of 35 and semi-minor axis of 20, with an azimuth of 29 for the major axis, a height of 3700 meters, and some flattening (0.15), try:

```
echo 200 400 29 35 20 3700 | gmt grdseamount -R150/250/350/450 -I1 -E -F0.15 -Gcat_ell_smt.nc
gmt grdview cat_ell_smt.nc -B -Qi -I+d -JZ2c -p195/20 -png ell
```

To compute the incremental loads from two elliptical, truncated Gaussian seamounts being constructed from 3 Ma to 2 Ma and 2.8 M to 1.9 Ma using a constant volumetric production rate, and output an incremental grid every 0.1 Myr from 3 Ma to 1.9 Ma, and internally use meters for horizontal distances, we can try:

```
cat << EOF > t.txt
#lon lat azimuth, semi-major, semi-minor, height tstart tend
0 0 -20 120 60 5000 3.0M 2M
50 80 -40 110 50 4000 2.8M 21.9M
EOF
gmt grdseamount -R-1024/1022/-1122/924+uk -I2000 -Gsmt_%3.1f_%s.nc t.txt -T3M/1.9M/0.1M -Qi/c -Dk -E -F0.2 -Cg -Mfiles.txt
```

The file files.txt will contain records with numerical time, gridfile, and formatted-time.

**Note**: There are many more examples of use, including working with grdflexure, in the test directory for the potential supplement.

## See Also¶

## Reference¶

Smith, J. R. and Wessel, P., 2000, Isostatic consequences of giant landslides on the Hawaiian Ridge, Pure Appl. Geophys., 157, 1097-1114, https://doi.org/10.1007/s000240050019.